Indian Roads Congress

Transcription

1 Revised Draft Report Prepared by CENTRAL ROAD RESEARCH INSTITUTE New Delhi Submitted to Indian Roads Congress New Delhi April 2011

2 Report Preparation Sudhir Mathur U.K.Guru Vittal T.Sanyal P.K.Choudhary Head, Geotechnical Engg Division, Central Road Research Institute Scientist F, Central Road Research Institute Geotech Advisor, Jute Manufactures Development Council In-charge, Geotech Cell, Indian Jute Industries Research Association

3 CONTENTS Page No 1 Introduction 1 2 Composition and Characteristics of Jute Fibre 1 3 Structure of Jute 6 4 Properties of Jute fabric 6 5 Manufacturing Process of Jute Geotextile (JGT) 8 6 Functions of JGT 10 7 Transportation, Storage and Handling of JGT 13 8 Properties of JGT & Important Test methods 15 9 Durability of JGT Environmental aspects of JGT Civil Engineering applications of JGT Cost of Jute geotextile and Commercialisation Laboratory Studies on Jute Geotextiles Some Case Histories / Field Demonstrations International Usage of Jute Geotextiles 71 Appendix I (JGT Manufacturing Photographs) 78 Appendix II (Equipment for JGT Testing) 84 Appendix III (List of Important Application Projects) 93 Appendix IV (Standards for Testing) 96 Appendix V (References) 98

4 Terms & Definitions 1. Bast: Belonging to group of strong, woody fibers, such as flax, hemp, or jute, obtained from phloem tissue and used in the manufacture of woven goods and cordage 2. Denier: A measure of the fineness or size of a yarn expressed in terms of mass per unit length; numerically equal to number of grams per 9,000 metres length of fibre 3. Tenacity of Fibre: Capability of fibre to keep a firm hold on objects without slippage 4. Separation: Segregation of two layers of materials by preventing their intermixing 5. Filtration: Process of retaining soil particles while allowing water to pass through 6. Erosion: Detachment of soil particles from a soil surface and the transportation of the detached particles to new location 7. Geotextile: Textile materials which are permeable, made by either woven or non woven process, used along with soil or backfill material for improving the performance of civil engineering structures 8. JGT: Jute geotextile Textiles made by using Jute fibres by adopting either woven or non woven techniques 9. Woven geotextile: Manufactured by weaving weft threads through warp threads, usually (but not necessarily) having stronger warp threads than weft threads. A textile structure comprising of two or more sets of filaments or yarns interlaced in such a way that the elements pass each other essentially at right angles and one set of elements is parallel to fabric axis. 10. Non woven geotextiles: Geotextiles produces from randomly distributed continuous filaments or staple fibres, which are bonded together chemically, thermally or mechanically or a combination of such processes 11. Jute netting: A type of open weave jute geotextile, having large openings between successive warp and weft threads, mainly used for erosion control applications 12. Percent Open Area (POA): The net area of a fabric that is not occupied by fabric filaments, normally determinable only for woven and non woven fabrics having distinct visible and measurable openings that continue directly through the fabric 13. Drapability: Bending ability of geotextile for making full contact with the soil and taking the shape of the contour of the soil surface.

5 14. Typical value: Refers to average value of the geotextile sample property, which should be determined by testing statistically sufficient number of samples 15. Minimum average roll value (MARV): Derived statistically as the average value minus two standard deviations 16. Pore size: The size of the opening between fabric fibres 17. Apparent Opening Size (AOS) or Equivalent Opening Size (EOS): AOS is a measure of the largest effective opening in a geotextile. AOS is determined by sieving glass beads of successively bigger size until 5 per cent or less pass through the fabric. 18. Clogging: The plugging of a fabric by deposition of particles within the fabric pores 19. Filter cake: A thin layer of fine soil particles accumulated in the soil adjacent to the fabric as a result of smaller soil particles being washed through the soil pores and the geotextile 20. Permeability, Longitudinal or in plane: The fabric property which permits a fluid, normally water, to flow in the plane of the fabric, also known as Transmissivity 21. Permeability, Transverse: The fabric property which allows a fluid, normally water, to flow through a fabric perpendicular to the plane of the fabric, also known as Permittivity 22. Coefficient of Permeability (Coefficient of Permittivity): A measure of the permeability of a porous media such as soil or geotextile to water. It is the ratio of discharge velocity to the hydraulic gradient under laminar flow conditions 23. Trench drains: Covered type of drains constructed in the sub-soil for lowering the water table or for effective drainage of sub-soil water 24. Puncture resistance: Resistance to failure of a fabric from a blunt object applying a load over a relatively small area

6 1. Introduction 1.1 India is the largest producer of Jute and allied fibres. It produces more than 60 per cent of the total jute produced all over the world. India and Bangladesh are the two major players in this field. In India major production of the jute goods are consumed domestically, whereas Bangladesh exports majority of its products to other countries. In India jute cultivation is confined to West Bengal, Eastern Bihar, Assam, Orissa, Tripura, Uttar Pradesh and to some extent in Meghalaya. Out of these states, West Bengal, Bihar and Assam contribute about 80 per cent of the total production. Figure 1, shows the picture of jute plant, jute fibre and jute bales. 1.2 Jute is a textile fibre, which when converted into fabric possesses many of the desired properties required for geotechnical engineering works and termed as Jute Geotextile (JGT). Textile materials in woven, non-woven or other forms, when applied to soils (geo) for improving its engineering characteristics are termed as Geotextiles. Use of synthetic geotextiles made up of polymeric materials like polypropylene, polyester etc, to address soil related problems in civil engineering is a well tried and accepted concept all over the world. Application of Jute Geotextiles (JGT) in this field, however, is a recent phenomenon. Natural fibres of jute can be processed as fine yarns which, in turn, can either be woven into permeable and drapable fabrics by appropriate weaving machineries (woven fabric) or can be matted together in a random manner (non-woven fabric). Different type of jute geotextiles are shown in Figure 2, 3, 4 and Both woven and non-woven fabrics have been used in many road projects successfully to facilitate construction, ensure better performance of the structure and reduce maintenance cost. The jute geotextiles have also been used in protection of river banks, in managing slopes including hill slopes, control of surface soil erosion, stabilisation of embankments, prevention of reflection cracks in bituminous pavements and consolidation of soft soils, etc. The enormous potential of jute geotextile is being increasingly appreciated by end-users because of its low price and technical feasibility. 2. Composition and Characteristics of Jute Fibre 2.1 Jute is a natural ligno-cellulosic bast fibre. Bast refers to a group of strong, woody fibers, such as flax, hemp, or jute, obtained from phloem tissue which are used in the manufacture of woven goods and cordage. Jute is highly hygroscopic and can absorb water upto about 5 times its own dry weight. This property introduces in jute an element of variance in weight under different relative humidity. Jute is a very good insulator of heat and electricity. This property also varies with the change in moisture content. The strand of jute fibre consists of numerous individual filaments, which form a meshy structure. These fibres have varying length, fineness,

7 strength, extensibility, tenacity, stiffness and toughness. The matured jute plant with a height of about three metre is cut and sun dried in the field. The plants with shaded leaves are tied in bundles and immersed in mild flow water for about two weeks for retting. The fibres are extracted from the plant, washed in clean water and sun dried to make it ready for use. The constituents of jute fibre are mainly Cellulose, Hemicellulose and Lignin. They are distributed in the fibre as shown in Table 1. Table 1: Composition of Jute Fibre. Constituents Percentage Cellulose Hemi Cellulose Lignin Others (Wax, Ash, Nitrogen etc.) 1 2 Jute Plant Jute Fibre Jute Bale Figure 1: Photographs of Jute Plant, Jute Fibre and Jute Bale

8 Figure 2: Jute geotextiles for control of surface soil erosion Figure 3: Jute geotextiles for filtration and drainage

9 Figure 4: Jute geotextiles for separation and filtration Figure 5: Prefabricated jute drains for accelerated consolidation of soft soil

10 2.2 Tenacity of jute is usually high and remains stable over a range of 30 per cent 80 per cent of relative humidity. Under very wet or very dry conditions, tenacity of jute decreases. Stiffness is a measure of resistance to bending (breaking stress/breaking strain). Stiffness of jute is high at normal moisture content but decreases with increase in moisture content above the normal. Torsional rigidity of jute is also affected at higher moisture content. Toughness of jute is low on account of its low extensibility. Toughness is defined as the area under stress-strain curve for the fibre under test. Some salient physical properties of jute are given below: Density 1.47gm/cc Average Fineness 20 denier (i.e., weight in gm of 9000 metres of filament) Tenacity 4.2 gm/denier Average Extension at break 1.2 per cent Average Stiffness 330 gm/denier Average Toughness Index 0.02 Hygroscopicity (average regain at 65 per cent relative humidity) 13 per cent 2.3 Jute fibres as already mentioned are natural fibres, comprising approximately 83 per cent to 87 per cent natural cellulose and 12 to 14 per cent Lignin. The fabric made of jute yarns biodegrades, leaving a fibrous residue. The other important feature of jute is that it does not draw upon the valuable nitrogenous reserves and ultimately decomposes, as is usually the case with other natural fibres. Jute geotextile acts like a straw or peat mulch aided by its degrading fibres, which help to retain the moisture and improve the soil-permeability. JGT possesses better drapability and also wettability, compared to all other geotextiles. JGT being the most hygroscopic among widely used fibres and is also more wettable than other fibres. This has been reported after a study was undertaken in this regard by Dr.T.S.Ingold and Mr.J.Thompson. The comparative physical properties of jute and other fibres are shown in Table 2. A brief description of the physical properties of jute fibre has also been given below Table 2. Fibre Table 2: Comparative physical properties of Jute and Other Fibres. Density (gm/cc) Fineness (denier) Tenacity (gm/denier) Elongation At break (per cent) Initial Modulus (gm/denier) Moisture Content (per cent) at 65 % RH Jute to Cotton Flax Kenaf Nylon Coir a) Tenacity It depends on thickness of the filament. It remains almost constant at per cent RH but decreases at very dry or wet condition. For conducting tenacity test on jute fibre, the fibre length is kept as 10 mm and time to break is kept as 10 seconds.

11 b) Elongation The elongation at break varies from 1.0 per cent to 1.2 per cent under normal atmospheric condition while in wet condition it increases marginally. c) Flexural Rigidity and Torsional Rigidity It is a measure of resistance to bending. This is quite high at normal moisture content. Flexural rigidity of jute ranges from 3.0 to 6.0 dynes cm 2. Torsional rigidity of jute reduces with increased moisture content. Modulus of Torsional rigidity (in x dynes cm 2 ) is of the order of 0.25 to These are measures of resistance of jute fibres (single fibre) against bending and torsion. d) Hygroscopicity Jute is highly hygroscopic in nature. Jute being the most hygroscopic among widely used fibres, is also more wettable than other fibres. The moisture retention capacity accelerates its spinnability and subsequent manufacturing processes. e) Thermal behaviour Like many other textile fibres, jute is a good insulator of heat. The transference of heat through the fabric is not only dependent on conductivity of fibre but also to a large extent on the volume of entrapped air in the fabric. 3. Structure of Jute 3.1 Strand of jute fibre consists of numerous individual filaments which are entangled at different places to form a meshy structure. Prior to spinning, entanglement of fibre mesh is mechanically broken into individual fibres. The fineness and length of an individual fibre may vary from 8 denier to 30 denier (gm/9000 m) and from a few mm to 300 mm respectively. 4. Properties of Jute Fabric Jute fabric is a tailor made product. The fabric is designed in such a manner that it possesses all the required properties suitable for specific geotechnical applications. Indian Jute Industries Research association (IJIRA) in collaboration with Jute Manufactures development Council (JMDC) have developed various types of woven, nonwoven, open weave JGTs for different end use applications in geotechnical engineering. Specifications of some typical JGTs are given in Table 2, 3, 4 and 5. Detailed explanation of the properties of jute fabric is given in section 8. As already stated, JGT is biodegradable. Hence available residual strength of JGT at the end of specified period would depend on the ambient conditions (e.g., type and properties of surrounding soil, temperature and moisture content, etc). Several case studies in fields showed that the strength of JGT typically gets reduced by about 60 to 70 per cent after lying embedded in estuarine soil for around 18 months. Exhumed samples of JGT from different projects often showed that integrity of the fabric remains unaffected despite strength reduction. Further R&D work is under progress in this regard.

12 Table 3: Properties of some typical Jute Geotextiles Parameters Woven Open mesh ASTM Test Methods Mass per Unit Area D 5261 (gm/m 2 ) Construction D.W.Twill Plain Plain Warp Count (lbs) Weft Count (lbs) Ends/dm Picks/dm Cover Factor Porometry (Apparent Opening size-aos in mm) 0.10 Aperture size-mm 8 x 8 13 x 11 Tensile Strength (kn/m) Warp Weft Roll width Available (cm) Minimum Length (m) (cut length) Maximum Length (m) (packing length/bale) Upto 457 (IS : 2873) Upto 820 Mill Practice Upto 550 Mill Practice Treatment Available Rot resistant Nil Nil and Bitumen Estimated lifetime 4 Years 2 Years 2 Years Water Holding Capacity- (Grey) Dripping Squeezed Normal Recommended Use 400% % 8 20% Separation and Filtration Road construction River/ Canal Bank Protection 500% NA 8 20% Erosion Control of Slopes Afforestation in Semi-arid Zone Road Surfacing 500% NA 8 20% Erosion control of Slopes Mine Spoil Stabilisation Landscaping D 4751 D 4595 Table 4: Open mesh woven jute geotextiles (IS Specifications) Properties Type 1* Type 2 Type 3 ASTM Test Mass per Unit Area (gm/m 2 ) D 5261 Threads/dm (MD X CD) 12 x x x 7 Thickness (mm) Width (cm) Open Area (%) Strength (kn/metre) (MD X CD) 10 x x x 12 D 4595 Water holding capacity on dry weight (%) Typical Durability (Minimum years) *Note: Type 1 open mesh JGT has now been removed from the IS Specifications

13 Properties Table 5: Woven Jute Geotextiles Grey (untreated) Rot proof Rot-resistant and bitumen treated ASTM Test Methods Mass per Unit Area (gm/m 2 ) and above 1200 D 5261 Threads/dm 102 x x x 39 (MD x CD) Thickness (mm) D 5199 Width (cm) Strength (kn/metre) (MD x CD) 20 x x x 21 D 4595 Elongation at 10 x x x 10 break (%) (MD x CD) Porometry (O 90 ) micron D 4751 Flow rate at 10 cm water head D 4491 (litre/m 2 /sec) Puncture Resistance (N/cm 2 ) D 4833 Typical Durability (Minimum years) Table 6: Nonwoven Jute Geotextiles (Indicative Specifications) Properties Type 1 Type 2 ASTM Test Methods Mass per Unit Area (gm/sq.m) D 5261 Thickness (mm) 4 8 D 5199 Width (cm) Strength (kn/metre) MD x CD 4 x 5 6 x 7 D 4595 Elongation at break (%) 20 x x 25 MD x CD Permeability Coefficient 3.4 x x 10 4 D 4491 (metre/sec) Durability (Years) 1 1 Recommended Use Construction of JGT encapsulated concealed rubble drains by the side of road and railways Drainage of water from cohesive fills Table 5: Properties of Pre-Fabricated Jute Drain with Coir Wicks Properties (Unit) PVD ASTM Test Methods Material Composition Sheath Core Jute Fabric Coir Yarn Width (mm) Thickness at 20 kpa( mm ) 9.0 D 5199 Weight of material/ linear m (gm) 140 D 5261 Material Tensile strength (kn) 4.5 D 4595 Elongation at break during 4 5 tensile test (%) AOS of jute sheath (O 90 ) Micron D 4751 Durability (Years) Minimum 1 5. Manufacturing process of Jute Geotextiles (JGT) 5.1. The coarse jute fibre is initially softened and made pliable by passing through the softener machine followed by application of emulsion (oil in water) and kept in pile form for about 24 hrs.

14 After cutting out the hard root portion from the bottom end, the fibre is mechanically processed through 2 to 3 carding passages when meshy (entangled fibres) structure is broken and delivered in form sliver. The sliver is thinned and made parallel by passing through 2 to 3 drawing passages. Sliver is then spun into yarn of different counts through slip draft or rove (for open mesh fabric) spinning frames. The spun yarn is then wound in spool in spool winding machine & ultimately to beam in beaming machine as warp thread and also in cop in cop winding machine as weft thread. In the weaving process, the warp and weft threads are interlaced with each other in the loom to manufacture woven jute geotextiles. For weaving open wave (mesh) fabric, bobbins are directly placed in the creel behind the loom as warp thread. 5.2 The non - woven jute geotextile is manufactured in different process. The waste jute sliver is fed into garneting cum cross lapping machine where the fibres are split out and randomly distributed over the conveyor and delivered in lap form with desired thickness. Generally one layer of jute scrim cloth is placed in between two layers of lapped sheets to add strength to the material. The lapped sheet is punched by needles in the needle punching machine for bonding the fibres mechanically to produce non-woven jute geotextile. Jute being a natural fibre, it degrades within a year when laid in contact with soil. Its durability can be enhanced by 2 to 3 years by treatment with rot-resistant chemical and also by bitumen treatment. Some photographs of manufacturing process are shown at Appendix I. The process flow of JGT manufacturing process is given as follows: Jute Fibre Softening Carding (Woven JGT) (Nonwoven JGT) Drawing Spinning Winding Beaming Garneting cum Cross lapping Needle Punching Packing Weaving Rot resistant & Bitumen treatment Packing

15 6. FUNCTIONS OF JGT 6.1 JGT, like the synthetic variety, improves the geo-technical properties of the soil on which it is applied. JGT, being permeable, allows the water retained within the soil to permeate across it and also along its plane. The extent of cross permeability (termed as permittivity) and inplane permeability (termed as Transmissivity) depends on the pore size of JGT (termed as porometry). The porometry of JGT determines the extent of soil particle retention on which it is laid. Properly designed JGT (in most cases, in relation to the mean diameter of the soil-grains i.e., d 50 ) arrests migration of the soil particles and imparts strength to the soil body. Properly designed JGT would perform the following functions: Separation Filtration and drainage Initial reinforcement Control of surface soil detachment Promoting vegetation growth or biotechnical support 6.2 Separation Separation function implies segregation of two layers of materials by preventing their intermixing, i.e., intrusion of one layer into the other comprising either dissimilar materials or similar materials with different grading. The phenomenon causes reduction in thickness of a particular pavement layer making the overlying structure susceptible to failure In road construction, separation is needed to segregate the sub-base from the subgrade for prevention of the excessive pavement deflection under axle loads of moving vehicles. Intermixing of two layers causes reduction in the thickness of a pavement to lower than the desired thickness. Load carrying capacity and the pavement life are consequently reduced Separation of two layers for at least one season cycle helps for gradual riddance of water from the base soil by use of JGT through concurrent functions of filtration and drainage. Experiments have proved that once this phenomenon takes place, chances of subsidence of a part of any road or structure due to intermixing become substantially less. Biodegradability of JGT therefore does not normally pose any technical impairment after a season cycle (about 12 months) of their application. 6.3 Filtration As already indicated in previous sections, JGT is supposed to perform two contrasting functions; soil retention and ensuring permeability of water through and along them. JGT provides a technically superior solution to traditional granular graded filters. JGT can be manufactured with pore sizes commensurate with the median grain size of the base-soil to ensure their retention. At the same time the requisite quantity of water is allowed to pass across and along JGT without causing to develop any differential pore water pressure. The functions of permittivity and Transmissivity are therefore important. With a tailor made JGT, differential water

16 over pressures across it can be effectively dissipated, preventing migration of soil particles concurrently JGT, like its synthetic counterpart, first retains the coarser particles of the soil. These coarse particles block smaller ones in the soil, which in turn prevents migration of even smaller grains. This phenomenon, which is known, as filter cake formation is in fact an indication of formation of natural filter within the soil. The situation can develop only if it is ensured that JGT has made full contact with the base soil (i.e. if drapability of the JGT is ensured). For ensuring full drapability, JGT requires to be suitable ballasted. This load on top of a JGT not only prevents its uplift under certain condition, but also protects the fabric from continuous exposure to weather Soil properly overlain by JGT is seen to develop filter cakes usually within a period of 3 to 4 months from the date of application according to laboratory tests carried out in Research Institutes. Development of filter cakes is a sure indication of the base-soil having attained natural stability. Once the soil attains natural stability, function of any separating fabric, be it synthetic or natural, becomes redundant. Though laboratory experiments by some researchers have shown formation of filter cakes within about 3 to 4 months from the date of application of JGT, it is advisable to ensure durability of JGT for at least one season cycle. Bio-degradation of a JGT therefore does not normally pose any deficiency in its expected performance for drainage or filtration Clogging is generally accumulation of particles on and into the openings of JGT. Soil particles at the base or particles in suspension of flowing water tend to block the pores of JGT by deposition on its surface or within its layer. Chemicals in water are sometimes responsible for chemical clogging of JGT. Performance of JGT is consequently adversely affected leading to progressive clogging. Such clogging may be allowed if the rate of deposition is very slow or for a limited duration. 6.4 Drainage JGT performs drainage function by conducting water. Proper drainage of soil accelerates its consolidation. The cohesion of the soil, as a result, is increased which, in turn, accentuates the separation effect of the JGT JGT possesses a high degree of Transmissivity, i.e., it can drain water effectively along their plane. JGT is also capable of holding water to about five times their own weight. In roads, lateral drainage of water from sub-base and subgrade is critical. JGT used as a separator may facilitate the lateral evacuation of water from the road-structure and prevent water accumulation at the subgrade level. 6.5 Initial Reinforcement JGT can reinforce soils, whose shear strength is low at the initial stages. Once the consolidation process takes place, there will be increase in the shear/ tensile strength of sub-soil

17 and hence there may no longer be need for JGT reinforcing layer. By facilitating consolidation of weak sub-soil when initial reinforcement is being provided by JGT, increase in tensile/shear strength of soil can be ensured after the consolidation process. Any large soil body e.g., an embankment, undergoes failure by vertical subsidence, lateral dispersion and rotational slides. When used in appropriate layers, especially across vulnerable planes of failure and distress, JGT can effectively control such failures. Soil movement is curbed by its confining action. JGT also absorb a part of the stress that could cause a shear-failure. Stability of such soil-structures is thus substantially enhanced enabling faster construction without removal of weak soil layers As has already been pointed out, any soil mass tends to stabilize naturally if proper separation, filtration and drainage and soil retention can be ensured. JGT can be manufactured upto 30 kn/m tensile strength in both warp and weft directions and can impart sufficient strength to soil body in the initial performing phase. Once consolidation has been achieved, stability improves, it has been established that the technical function of a geotextile natural or synthetic, becomes redundant. 6.6 Control of Surface Soil detachment Surface soils get eroded due to detachment of the particles by raindrops, splash and surface run-off during and after the rainfall and their transportation elsewhere. Such detachment may also be caused due to strong wind JGT (in fabric form) control erosion of any surface soil basically in two ways. First, they give a protective cover (partial or full) to the exposed soil surface. Secondly, they control migration of a portion of the soil particles by reducing the flow of surface run-off. The finer particles are mainly transported leaving the coarser grains to remain in position. This phenomenon reduces the erodability coefficient of the soil. JGT absorb a large part of the kinetic energy of raindrops and control rain splash detachment. To promote vegetation growth and thereby to arrest soil erosion open weave JGT (instead of fabric form) can be used. Open weave JGT acts as miniature check-dams or a sort of micro-terraces which prevent, to a large extent, the detachment of soil particles, help in precipitation and reduce the velocity of surface flow JGT holds many advantages over other types of getoextiles in controlling surface soildetachment and consequent erosion. JGT, as already stated, can retain almost 5 times their own weight of moisture, can attenuate extremes of temperature, can provide protection to seedlings from the direct sunrays, can prevent dehydration of soil, allow air and light through their open structures and provide nutrients to the soil after their biodegradation. 6.7 Bio-technical Support JGT facilitates, quickens and supports growth of vegetative cover on them. Once vegetation is grown, the function of JGT virtually ceases. Vegetation so grown, besides dissipating substantially the kinetic energy of rain-drops, serves as a receptor of moisture with the help of the leaves and the stems. The wind effects are also attenuated by vegetation. The

18 velocity of surface run-off is also reduced by virtue of the surface rugosity (roughness) of the vegetation. The root system ensures soil-attachment and imparts strength to the soil-body. Soilporosity and permeability are also improved, helping to control erosion. And finally, vegetation provides a sustainable solution to the problems of erosion control. JGT, a natural product, enhance vegetation-growth and together they provide a bio-technical solution to the problem of soil-erosion The choice of species of vegetation depends on the nature and composition of the nature and composition of the soil, which vary from place to place. Live sods of perennial turf-forming grass may be laid on embankment slopes, verges (earthen shoulders) and in other location. Proper preparation of the soil bed, application of manure and lying of JGT are basic prerequisites for growth of a good vegetative cover To ensure quick growth of vegetation, selection of the right type of vegetation species is extremely important. Studies have revealed that JGT enhance micro-climatic conditions (like temperature, soil-moisture) and organic matter-levels in soil, which are conducive to quick and sustainable growth of vegetation Laboratory and analytical studies have been carried out at CRRI concerning the role of vegetation in improving the stability of slopes. It has been established by laboratory testing that the binding effect of roots imparts to the soil a cohesive strength equivalent to a minimum of 2.0 to 2.5 ton/m 2. Assuming an effective depth of penetration of 0.5 m and increase in cohesive strength of 2.0 ton/m 2, analysis has shown that under certain conditions of slope geometry, a significant increase in the factor of safety is estimated up to a depth of about 6 m. Thus, by providing a vegetative cover, not only the erosion of the slope is checked, but also the possibility of shallow failure averted, due to the strengthening of the top 0.5 m of the hill slope. 7. TRANSPORTATION, STORAGE & HANDLING OF JGT 7.1 JGT can be easily handled and transported. Jute yarns are basically robust provided care is taken to keep them free from moisture (being hygroscopic) and fire. JGT can be shipped in rolls or bales either as a bulk or a break-bulk cargo. A bale weighs around 340 kg. (680 m 2 ) and may consist of a number of lengths (8 to 10) depending on the required individual roll length. 7.2 Storage Prolonged storage of JGT in warehouse is to be discouraged, as JGT is susceptible to microbial action and loss of strength. JGT should be provided with a water-proof cover for protection against rains. Direct contact with soil during storage should also be avoided. Jute should not be stored in a wet condition. Humidity, temperature variation, lack of air-circulation and abnormal moisture absorption affect the quality of JGT. Storage of JGT therefore calls for attention. The main thrust should be on safe transportation and storage of JGT at site without damaging and unduly exposing the material to adverse climatic conditions.

19 7.3 Site unloading A fork lift or front end loader fitted with a long tapered pole (carpet pole/stinger) is recommended for unloading JGT rolls. The carpet pole is inserted into the core of the JGT roll, which is then unloaded from the truck. Nylon straps/ropes/roll pullers may also be used. Not more than three JGT rolls should be lifted /unloaded at a time. Use of chains & cables for unloading purposes is to be discouraged. A tarpaulin, a sheet of plastic or the like should be placed on ground for initial storage of JGT. 7.4 Site Handling As already stated, JGT rolls should be provided with a protective wrapping. It should be kept above the ground and should be covered with a tarpaulin or an opaque plastic sheet. Exposure of JGT to moisture/water may pose handling problems. As JGT can absorb water upto 5 times its own dry weight, handling wet JGT becomes more difficult than handling a moisturefree JGT. The cores of JGT-rolls usually made of laminated paper are susceptible to damages on being exposed to moisture/water and should therefore be kept dry. JGT should not normally be stored for a long period. Protracted storage of JGT may reduce their strength to some extent. 7.5 Installation The soil surface on which JGT is decided to be laid should be made free from sharp aggregates, stones etc. Undulations should be levelled. JGT should normally be laid by unrolling the JGT from top towards the bottom where there is vertical difference in ground levels e.g. in slopes, banks of waterways etc. care should be taken to ensure that the fabric touches all points of the base-soil and is in intimate contact with it The next step should be to secure the JGT so laid with U-shaped staples made of 11 gauge wire at an interval of 150 mm normal to the slope unless otherwise recommended. It is advisable to use suitable wooden pegs as iron staples may get rusted on exposure. The length of staples to be used depends on the softness of the soil. If a soil is soft, i.e., easily penetrable, longer staples should be used for a greater pull-out resistance. A manual test for pull out should be made before finally hammering the staple down. Suitable non-metallic staples fabricated from biodegradable plastics may also be used. In addition to split bamboo pegs, steel staples (U shaped) of dimension 50/150 mm may also be used as per Guidelines issued for JGT application in Railway Embankments A wet JGT shrinks on drying. When JGT is to be laid in a wet condition, it should not be laid fully taut as the shrinkage sustained by JGT may pull it out of its initially placed position. The two ends of JGT roll should be properly anchored in a trench at least 500 mm deep and a spadewidth wide (for digging convenience) unless specified otherwise. The trench is to be backfilled with heavy stones/boulders in addition to stapling on the vertical and horizontal faces of the trench at an interval of not less than 150 mm Longitudinal edges should be provided with an overlapping of 100 to 150 mm and stapled at 100 mm c/c. unless otherwise recommended. Overlapping between the end of the upslope roll and top of the next downslope roll (i.e. the width-wise overlapping) should be at least 200 mm

20 secured by stapling at an interval of 100 mm c/c. unless otherwise recommended. Plantation of seedlings can be made after laying of the JGT through openings made as desired. Seeds may be spread on the prepared base-soil both before and after laying of JGT. 8. PROPERTIES OF JGT AND IMPORTANT TEST METHODS 8.1 In view of absence of code of practice for all varieties of JGT, the selection of the right type of JGT for specific application is of vital importance. Reliance on the available standards in the synthetic geotextiles is therefore unavoidable. Even the test standards of synthetic Geotextiles are not uniform across the world. Reference has been made to the American Standards (ASTM standards) for the sake of uniformity, wherever necessary Bureau of Indian Standards (IS) codes of practice have also been given. The properties of JGT have also been drawn from Jute Geotextiles A Survey made by International Trade Centre, UNCTAD/GATT where deemed applicable. The section is subdivided into three categories. Physical Properties Mechanical Properties Hydraulic Properties 8.2 Physical Properties Physical properties mentioned in this subsection refer to JGT as manufactured. indicative only, and not the critical design properties of the product. They are Mass per unit area The weight of the fabric is mass per unit area and it is expressed in gram per square metre (gsm). This is an important property having a direct impact on the cost and mechanical properties. After 24 hours of conditioning at standard ambient conditions of 21 0 C ± 2 0 C, relative humidity 65 per cent ± 5 per cent, the following nomenclatures for civil engineering application may be adopted in case of untreated JGT in respect of mass per unit area. i) Light weight 290 to 300 gm/m 2 (usually referred to as gsm ). ii) Medium weight 400 to 500 gm/m 2. iii) Heavy weight 700 to 1000 gm/m 2 Note: i) International Trade Centre recommends 500 mm x 500 mm sample sizes for tests. ii) The weight should be measured to the nearest 0.01 per cent of the weight of total specimen. iii) Mass, length and width should be measured without tension. iv) The current test procedure for this property is ASTM D Thickness This is an important property in connection with Transmissivity of JGT. It is measured between the upper and lower surfaces of the JGT at a specified pressure (2 kpa). ASTM D 5199/IS-

21 13162 Part-3 stipulate that the accuracy should be at least 0.02 mm under a pressure of 2 kpa. Thickness of commonly used JGT ranges from 1.5 mm to 5 mm. Thickness of JGT influences the Transmissivity of fabric Porometry (AOS) Porometry is the size of the pores present in a woven fabric and is a critical property for permittivity and soil retention. JGT can be manufactured with an open mesh ( Soil saver usually with the pore size of 2.84 cm 2 for medium weight JGT) or with closely woven mesh with a pore size upto a fineness OAR (Open Area Ratio) reducing permittivity and inducing clogging. Based on the soil particle size distribution pore size of the fabric can be designed as fine as 100 micron. Pore sizes can be measured by three different techniques By Microscope By using a calibrated microscope in the case of rectangular pores, the smaller dimension is taken as the pore size. A grading curve for the pore size distribution can then be represented on a semi-logarithmic graph, which is similar to a particle size distribution graph for a soil. By Reverse Dry Sieving Technique Special glass beads (ballotini) of known size are vibrated on the JGT-fabric having unconfirmed mesh-size or porometry. The percentage of the glass beads passing through it is recorded and the test is repeated for successive smaller grades of glass beads. The pore size vs. grading curve may be drawn on the basis of the findings. However, It may be noted that the weight of glass beads and the extent and nature of vibration applied for this test are yet to receive universal acceptance. By Wet Sieving The standards for this test vary widely and is therefore not stated Drapability It is the bending ability of fabric in making full contact with the soil and taking the shape of the contour of the soil surface. Drapability of wet jute fabric is more when compared to its dry state. JGT should have the ability to shape itself in keeping with the soil surface contours and to establish full contact with the surface. The extent of drapability is assessed by measuring the sag (D) in mm of the JGT in between two points (S) also in mm. Drapability of jute is more when it is wet. Drapability can be a measure of JGT s flexural stiffness, i.e., bending of JGT under its own weight between two points (vide test method in ASTM D 1388). Open weave JGT possesses a better drapability than its synthetic counterpart. A study on drapability of JGT and synthetic geotextiles was taken up by Dr.T.S.Ingold and Mr.J.Thompson. They tested drapability of JGT and synthetic geotextile by placing the samples (of equal unit weight) over an open span and measuring the sag during dry state as well as wet state of the fabric. It was noted by them that sagging of JGT (in both dry as well as wet state) was much more than synthetic geotextiles. In other words, JGT hugs the ground in a much better manner than synthetic geotextiles.

22 8.3 Mechanical Properties Mechanical properties of JGT are basically indicative of the product s resistance to mechanical stresses developed as a result of application of loads and/or installation conditions. The tests that may be used for determining mechanical properties of a JGT are tensile strength, puncture strength, burst strength and tear strength. Test for friction resistance (soil-jgt friction) is also considered to be important Tensile Strength The test for Tensile Strength should be in keeping with ASTM D In case of woven JGT, either ASTM D 4632 or IS 1969 can be followed. The test specimen size of JGT normally taken for testing is 20 cm x 10 cm. The JGT specimen is stretched by gripping it at two ends till its failure. When extending the sample, both load and deformation are to be measured and noted. Other tensile test methods are Narrow Strip Test (ASTM D 751) and Wide Width test (ASTM D 4595/BIS Part 5). A sample of 20 mm and 500 mm width respectively serve the purposes for the aforesaid tests. Maximum tensile stress is often referred to ultimate strength. Woven JGT (heavy type) can be manufactured to an ultimate strength of 30 kn/metre under normal manufacturing process. Commonly used woven JGT have the tensile strength in the range of 20 kn/m to 30 kn/m. The stress-strain curve of JGT sample indicates the following: Maximum tensile stress Strain at failure (i.e., elongation at break) Modulus of deformation (i.e., the slope of the initial portion of the stress-strain curve) Toughness (usually the area under the stress-strain curve) Puncture Strength This is the resistance to puncture of JGT. A puncture rod is pushed through the JGT sample clamped to an empty cylinder. Resistance to puncture is measured in N. Woven JGT (heavy type) may be manufactured to possess puncture strength of 400 N Burst Strength This test is also known as Mullen Burst Test and is described in ASTM D The JGT is given a shape of a hemisphere by inflating it by a rubber membrane. The sample bursts when no further deformation is possible. This is an index test and is used basically as a quality control test. The unit is kilo Pascal (kpa) Tear Strength This test is performed in tensile strength testing machine. JGT should be inserted into a tensile testing machine with an initial 15 mm cut. The load stretches the fabric before it tears. The test is described in ASTM D 4533/IS The unit is kilo Newton (kn).

23 8.3.5 Frictional Resistance This property can be determined either by the direct Shear Test using a shear box or the Pull out Test. The sample is placed between two parts of a shear box with its lower half fixed. The upper half filled with soil is moved horizontally relative to the lower half at a constant rate of displacement. The maximum horizontal force required to move the top half is used to calculate maximum horizontal shear stress by dividing it by the specimen area. In the pull out test, the JGT sample sandwiched between two halves of the box fitted with the soil is pulled by the jaws at a constant rate of displacement. The pull-out forces is a function of JGT-extensibility, length of embedment, redrawal stress etc. It may be noted that determination of values for different test indicated above depends largely on the testing procedures like the method of gripping the sample, slippage of the sample, rate of deformation, sample-size etc. Hence following standard procedure is extremely important for repeatability of test results. 8.4 Hydraulic Properties The major hydraulic properties of a JGT are permittivity and Transmissivity. These properties act in conjunction with their soil-retention capacity. JGT help stabilize the adjacent soil-structure by developing filter cakes under unidirectional flow conditions and together they control the ultimate flow-capacity of the system. In unidirectional flow conditions, initially there is loss of fine soil particles through the pores of JGT leaving gaps in its soil-structure immediately contiguous to it. Larger particles bridge over these gaps as in arches as well as over the pores in JGT. Once larger particles rush to form the so-called bridges, passage of smaller particles are blocked and a graded filter naturally develops in contact with the JGT. Research in this field has confirmed that even fairly uniform sands can bridge a regular meshopening of two to three times the mean particle size (d 50 ). In reversing flow condition (twodirectional flow) such graded filters within the soil zones adjacent to JGT may also develop provided there is sufficient cycle time. In such cases of reversal of flow, a combination of JGT and granular filter is often considered necessary. Formation of filter-cakes depends on compatibility of distribution of pore-sizes in JGT vis-à-vis grain size distribution of the contiguous soil. If the pore sizes in a JGT are too large, there may be substantial initial loss of soil particles in range of sizes. This is in effect a phenomenon of internal erosion. When voids created by internal erosion are large, the soil-body as a whole becomes vulnerable. Suffusion is also a type of internal erosion, confined to finer particles in a soil-matrix without shift of position of larger particles. Suffusion is less damaging than internal erosion as it does not contribute to destabilisation of the soil-matrix as such. Pore size of JGT is important and should be judiciously chosen. Larger than the optimum pore size may lead to internal erosion while lower than the optimum pore size may cause clogging. As already stated, permittivity and porometry of JGT are two contrasting functions. Permittivity of JGT depends on permeability of the soil. Soil retention is obviously more effective with smaller

24 pore-size, which however, reduces its permittivity. A judicious compromise is therefore called for in for selecting a JGT with proper porometry. IRC SP 59 provides guidelines for selection of polymeric geotextiles based on in-situ soil characteristics and Permittivity and AOS properties of geotextiles. These may be referred to while using JGT also. However producing JGT with AOS lesser than 100 microns may not always be feasible. In such situations, a sand cushion of 25 to 50 mm can be laid below and above JGT Soil Permeability (k s ) Permeability of the soil can be measured in a laboratory. This property is indicative of soil flow capacity under a given hydraulic gradient and flow-area as per Darcy s Law. q = k s x i s x A Where q = unit flow rate, k s = coefficient of permeability of soil i s = hydraulic gradient. A = total cross-section of flow. The equation can be expressed as q = K s x Δh s /L x A or K s = q x L/ Δh s x A Where Δh s = change in hydraulic head or head loss across soil L = length of flow path or soil thickness over which Δh s occurs K s = is expressed in cm/sec Permittivity of JGT One of the major functions that geotextiles perform is filtration. In filtration, the liquid flows perpendicular to the geotextile into crushed stone, a perforated pipe, or some other drainage system. It is important that geotextile allow this flow to occur without being impeded. Hence the geotextile s cross permeability must be quantified. The fabrics deform under load. Thus a new term, permittivity, has been introduced to express the permeability of geotextiles. It is expressed as amount of water moving across a geotextile in unit time through unit area and at unit head. It is usually referred to as K n /t, where K n is permeability normal to the geotextile (metre /sec) and t is thickness in metre. If permittivty of JGT is known, the flow capacity of JGT can be assessed for any giver hydraulic gradient and flow area. It is expressed in reciprocal of time (sec - 1) and is deriver from Darcy s Law. q = K g x i g x A = K g x Δh g /t g xa where k g stands for coefficient of permittivity of JGT, h g = hydraulic gradient (Δh g /t g ) Δh g = headloss across JGT A = JGT cross-section The ratio k g /t g is termed as the permittivity of JGT and is therefore equal to a/δh g xa

25 8.4.3 Transmissivity For the flow of water within the plane of geotextile (e.g., in the utilization of drainage function), the variation in geotextile thickness (its compressibility under load) is again a major issue. Therefore the word Transmissivity was introduced. The in-plane permeability along the geotextile plane is referred as Transmissivity. It is expressed as K p.t (K p is expressed in meter/sec, t is thickness in meter and Transmissivity is expressed in m 2 /sec) Determination of clogging potential of JGT There are two test methods available to evaluate clogging potential of JGT Gradient Ratio test and Hydraulic Conductivity Ratio (HCR) test. The first method does not simulate the field conditions in respect of compaction and confinement, which the latter method does. ASTM D 5567 describes methods for the HCR test. ASTM D 5101 mentions about the Gradient Ratio method in which water is allowed to flow downwards through a vertical column of the soil placed over the candidate JGT. The hydraulic gradient is measured at two locations above the JGT. If the ratio of the flow exceeds a prescribed limit, it indicates the vulnerability of the JGT to clogging. The intention of either of these two methods is to ensure a long term flow compatibility between soil and JGT. Clogging-proneness of a JGT is low when the flow rate test decreases with time and then attains a stable value over a time. Clogging potential is high when the flow rate continues to decrease with time and does not stabilize. Piping failure is indicated when the flow rate goes on increasing with time. Some of the testing equipment available in India to test jute geotextiles are shown in Appendix II. 9. DURABILITY OF JGT 9.1 It has been established after several laboratory tests on samples of JGT with varying linear density that its biodegradation depends on environmental factors. It has also been observed that jute degrades faster in an acidic ambience having ph value less than 5.2. The rate of degradation of JGT is generally fast in the initial stages, but slows down subsequently. On the other hand, when ph is in a higher range (above 7) i.e. in an alkaline environment, the laboratory tests conducted by IIT, Delhi have initially revealed that higher the linear density of yarns in a JGT, quicker is its degradation, though more elaborate studies are needed for this purpose to come to a definite conclusion. As already stated in section 4, several case studies in fields showed that the strength of JGT typically gets reduced by about 60 to 70 per cent after lying embedded in estuarine soil for around 18 months. 9.2 Bacteria and fungi are two main groups of micro-organisms responsible for the microbial decomposition of any natural geotextile. Moisture plays a key role in this respect. It has been reported that the minimum moisture requirements for the growth of bacteria and fungi in JGT are 20 per cent and 17 per cent respectively. Jute attains the aforesaid moisture contents when the relative humidity in the atmosphere is above 80 per cent.

26 9.3 Temperature is also instrumental for bacterial and fungal attacks on the jute. A temperature of 37 0 C is the optimum temperature for bacterial growth and 30 0 C for growth of fungi in JGT. Both sunlight and rain causes quick degradation of JGT. The organic content accelerates the decay of jute fibre. The degradation studies on jute so far conducted indicate that the mechanism of its biodegradation is complex, being dependent on interaction of a number of influencing factors. 9.4 In order to increase the life of jute geotextiles, jute geotextiles have been successfully treated with bitumen, copper based chemicals, phenol and some other patented chemical compounds. However, few environmentalist expressed a view that chemicals should be so selected that may not pollute the ground soil and water. The jute mills have therefore after several deliberations have decided to treat jute geotextile with COMPSOL (trade name) which is a Copper Ammonium Carbonate solution prepared to meet the U.S. and Canadian WHMIS (Workplace Hazardous Materials Identification System) standards. It is an aqueous solution containing Copper as Copper Ammonium Carbonate (5-10 per cent ml/litre and Ammonium Hydroxide 6-15 per cent ml/litre). The remaining ingredient is water and other components, present in less than 1 per cent concentration. It is claimed that these component have no significant additional hazards. The compound is stable, does not cause hazardous polymerization, and is not compatible with strong acids. No toxicological data is available on Copper Ammonium Carbonate, though Ammonium Hydroxide is mildly toxic. There is no cancer causing agent in the compound. It is not irritating to contaminated tissues. It does not produce mutagenicity (change in genetic material), embryo toxicity, teratogenicity (damage to developing foetus) and reproductive toxicity. Other properties of COMPSOL are given below: Specific Gravity 1.20 at 150 C Solubility Completely soluble in water ph 9.9 at 15 C Evaporation rate Similar to water Freezing point Minus 5 0 C 9.5 Bitumen as water-repellent Normally 90/15 Grade Industrial bitumen is used. Modified bitumen and polymerized bitumen have not been tried. As a result of the application of rot resistant chemical or bitumen, the life of a JGT can be prolonged to about 2 to 5 years, subject to the specific subsoil environment. As already stated in section 4, several case studies in fields showed that the strength of JGT typically gets reduced by about 60 to 70 per cent after lying embedded in estuarine soil for around 18 months. 10. ENVIRONMENTAL ASPECTS OF JGT 10.1 Jute, being an agricultural produce, poses no adverse environment impact. Besides its cultivation, its processing and manufacture are essentially pollution free. A study by Dundee University reveals that jute processing has not caused any illness to workers engaged in the job

27 for as long as twenty years. Quantities of chemical pesticides/fungicides and fertilizers that are usually necessary for jute cultivation are far less than those required for cotton cultivation. Jute cultivation facilitates multiple cropping pattern, enabling farmers to increase their field outputs. Jute cultivation precedes paddy and pulse cultivation in that sequence. Leaves of jute plants enrich the soil fertility As already mentioned fibres are extracted from jute plants by retting. Water in retting tanks does not affect natural drainage nor does it pollute ground water. In fact, the retted water can be used for irrigation for watering crop fields. Testing of jute fibres reveals that proportions of pesticide/fungicide and fertiliser-residues are insignificant. Studies conducted by Indian Jute Industries Research Association (IJIRA) and Central Pollution Control Board show no adverse environmental impact of the effluent released from jute mills Hydrocarbon emission from jute batching oil (JBO) has also been rigorously studied by IJIRA. The waste batching oil emulsion is mostly recycled for processing of jute without posing any environmental threat. An alternative batching oil (rice bran oil) has recently been developed by IJIRA which is a non-polluting lubricant. During manufacture of jute yarns, other ingredients used like starch, natural gum are found to have no adverse environmental impact Environmental Protection Encouragement Agency (EPEA), Hamburg in Germany, a research and consultancy body, and the FAO Secretariat have made a comparative study between jute and polypropylene (PP) in respect of waste generation, water requirement, energy consumption and CO 2 emission in their production. The Table 8 below indicate the same. Table 8: Comparison of environmental effects of Jute & PP fibres per ton basis Parameter Jute PP Ratio (PP/Jute) Waste produced (tons of Waste/ton of product) Water Consumption per ton of 54 to to 0.02 product (m 3 ) Energy Consumption per ton 5.4 to to 15.6 of product (GJ/t) CO 2 emission (tons of CO 2 /ton of product) -1.2 to to Jute geotextiles (JGT) evidently pose no environmental threat. Being biodegradable JGT ultimately coalesce with the soil on which it is laid, adding nutrients to it and retaining water for quicker growth of vegetation. Unlike synthetic geotextiles which are not biodegradable, JGT have no disposal problems. 11. CIVIL ENGINEERING APPLICATION OF JUTE GEOTEXTILE (JGT) There are several areas of application of JGT in Civil engineering which have proved effective after field trials. These are listed below: - Surface Erosion Control in Slopes - Bank Protection in Rivers and Waterways. - Erosion Control in Slopes

28 - Stability of Embankments for Highways. - Strengthening of a Road-structure. - Shoulder Drainage - Consolidation of Soft Soil. - Prevention of reflection cracks Design approach, installation-method, and suitability of the type of JGT for the intended use are indicated separately for each application hereinafter Surface Erosion Control The most popular use of JGT has been for erosion control purposes. It has been in use since 1950s when it was developed and exported to Europe and USA in the name of Soil Saver of Geo-jute. Geo-jute is a structure made of jute fibres woven into a heavy open mesh. It was mainly used for protecting newly cut slopes from erosion through growth of vegetation. Geo-jute has good tensile strength, is flexible, easy to install and biodegradable and is thus environment friendly. Geo-jute is normally available in rolls of 1.22m width and 70m length. The open mesh size of geo-jute net may be 16mm x 22mm or as per the requirement of the application site The purpose of natural geotextile is to protect and support the natural environment for a limited time span. The task is complete when nature, through soil and vegetation, eventually provides adequate protection. The natural geotextile, therefore, provides temporary aid for the establishment of natural vegetation. Once the vegetation cover is established, the shrubs and plants themselves act as cover to the surface to prevent erosion in the long run. Thus JGT acts as bio-engineering or engineered agronomic system for erosion control i.e. engineering and vegetative measures used in conjunction with each other to fulfil the ultimate goal of erosion control. Ingold and Thomson (1990) carried out studies on the erosion control characteristics of different geo-textiles in sandy loam soil on 1 V:2 H slope and found that geo-jute reduced the soil loss to about 1.3 gm/mm from control. The mean erodibility for synthetic mat was found to be about 5 gm/mm. Rickman (1988) reported the soil loss in geo-jute as 14 per cent of the control. With a growth of good grass cover the protection efficiency of geo-jute can be in the range of 99.0 to 99.9 per cent with a crop factor of 0.00 to 0.01 (Ingold and Thomson, 1990). Tests carried out by them further showed that natural fibre net such as geo-jute significantly reduces the splash erosion by rain drop impact. Geo-jute strands absorb much of the runoff and ponded water within the miniature check dams which the JGT strands provide. Water absorption capacity of open weave JGT is about 4-5 times its dry weight. The good absorbency of geo-jute has much to do with its runoff control ability. Once jute absorbs water to capacity, its flexibility is increased approximately, 25 per cent thereby improving its drapability, i.e. its ability to maintain intimate contact with soil, which further helps in reducing erosion. Ingold and Thomson (1990) reported that the runoff with application of jute net is reduced to about 15 per cent compared to 42 per cent in the control.

29 It is obvious that when the rainfall intensity exceeds the permeability of the base-soil, surface run-off results in transporting the detached soil particles. Rain-drop impact is the prime agent in detachment of soil-particles while the surface run-off is the main transporting agent. It may be noted that the extent of surface soil-erosion depends on other factors as well namely, the nature and extent of vegetative cover, inclination of the surface, length of flow etc. Table 9 below shows a correlation between rainfall form and kinetic energy. Table 9: Correlation between rainfall intensity and kinetic energy Rainfall form Intensity (mm/hour) Diameter of rain drops (mm) Kinetic Energy (j/me/hour) Drizzle < Light Moderate Heavy Excessive Cloudburst to The netting structure of the geo-jute provides innumerable miniature check dams in the flow or runoff which trap fine soil particles and a part of runoff, thereby improving soil moisture status. The heavy strands of jute absorb the impact of falling rain drops and check splash erosion. The open mesh provides protection to seeds and plants sown from washing away by runoff. The jute mat also functions as a mulch to maintain humidity and regulates temperature for proper seed germination. Thus, geo-jute creates improved micro-environment for the growth of vegetation and biodegrades in due course (which may take place in about two years) adding additional organic matter to the soil JGT have to perform usually two contrasting functions namely, soil retention and permittivity. It is always advisable to develop a vegetative cover over the affected soil surface. JGT s function ceases once the vegetation is fully grown and reinforces the soil. Untreated JGT have a useful life of one season (generally) by which time the vegetation has to grow. Decomposition of JGT adds nutrients to the soil, besides acting as a water receptor. recommended that the laying of JGT along with seeding are so timed as to take advantage of the increased moisture content of the soil from the monsoon showers. JGT possess the highest moisture absorption capacity of all fibres natural or synthetic about 500 per cent of its own dry weight and much higher than that of two other natural fibres in use as natural geotextiles namely, Sisal (175 per cent) and Coir (150 per cent). It is Design Approach The porometry and the strength of JGT are the basic criteria for design. Soil loss by detachment and transportation is prevented initially by JGT, which will be subsequently be done by the vegetative cover. The vegetative cover controls erosion naturally after degradation of JGT. Kinetic energy of rain-splash is dissipated by JGT before vegetation takes over the function.

30 Slope, composition of soil and rainfall are guiding factors for choice of the type of JGT. The design-approach may be three pronged: Agronomic (biological) Land/soil management Mechanical JGT is useful tool for agronomic control by helping in rapid growth of vegetation. Land/soil management also needs JGT. Mechanical methods are, in fact, manipulation of the surface topography by construction of terraces/benches or silt fences. JGT maybe used as a component of the slit-fence. Each or a suitable combination of the three methods is necessary for surface erosion control. The types of JGT useful for the purpose are indicated below: Type I Weight 750 gm/m 2 May be used where Aperture size 20x20 mm - Soil type is mixture of coarse to very Thickness 7 mm coarse aggregates like rock-particles. Thread/m (warp x weft) 70x70 - Steep slopes up to 45 0 Tensile strength 30 x 20 kn/m - Annual rainfall upto 3000 mm (warp x weft) Type II Weight 500 gm/m 2 May be used where Aperture size 25x25 mm - Soil is mixture of silt and sand or Thickness 5 mm clay Thread/m (warp x weft) 65x45 - Moderate slopes (45 0 to 30 0 ) Tensile strength 25x 20 kn/m - Annual rainfall upto 3000 mm (warp x weft) Type III Weight 300 gm/m 2 May be used where Aperture size 25x25 mm - Soil is sandy clay Thickness 3 mm - Gentle slopes < 30 0 Threads/m (warp x weft) 100x120 - Annual rainfall upto 2000 mm Tensile strength 20 X 15 kn/m (warp x weft) Application Method The soil-surface is to be levelled without any sharp aggregate protruding over it. if necessary, the slope may be re-graded to the angel of internal friction of the soil prior to levelling. Broadcasting of seeds of appropriate vegetation. Unrolling of JGT from top of the slope to the bottom or along the direction of surface runoff. Anchoring of JGT by steel staples/wooden pegs within a trench at the two ends.

31 Note: Care should be taken ensure drapability of JGT i.e., the fabric must touch the ground at all points. Overlaps should be 10 cm at the sides and 15 cm at the ends. Second dose of seed broadcasting should be done over the laid JGT along with dibbling of locally available grass. Selection of the type of vegetation is very important. Sowing/planting procedures are not uniform and depend on the types of species, soil-composition, rainfall etc. Local experience should be the guide. Taking help of botanists, agronomists, local Forest Departments for selection of species, timing of sowing/planting, planting/broadcasting procedures, procedure of their nurture and maintenance etc, are strongly advised Monitoring Close monitoring should be carried out for at least one season cycle. Displacement of JGT, of any, is to be noted and watched without disturbing it initially. Torn portions of JGT may be over lapped by fresh JGT pieces duly stapled on all sides. Watering/maintenance of the plant-saplings may be done as per procedures suggested by the botanists/agronomists/forest department, as the case may be Bank Protection of Rivers and Waterways The main causes of bank erosion are as follows: i) Weak bank soil which is easily erodable. ii) Strong current and eddies near the bank. iii) Waves induced by wind and moving vessels. iv) Large fluctuations in water-level v) Uplift pressures due to alternating hydraulic gradients Bank erosion may be controlled effectively either by repulsion of flow away from the affected banks or by providing a durable protection to the affected banks or by a combination of both these measures. Repulsion of flow is a task of the concerned engineers and can be achieved by construction of suitable regulatory measures at appropriate locations. Protection to the banks can be done by a combination of conventional granular filter /armour and JGT. The top of the bank protection work should have a cover of vegetation (e.g., quick growing local grass, vetiver grass, mangroves in saline inter-tidal zones) The basic function of JGT in bank-protection in rivers and waterways is filtration as a more precise alternative to conventional granular filters. Filter design for erosion-control in banks of rivers, canals and waterways should address three basic criteria: i) Design of JGT ii) Survivability of JGT iii) Durability of JGT

32 The design basically involves selection of a Jute Geotextile (JGT) which will ensure soil tightness and proper permittivity of water to prevent differential over-pressures from developing across it. It has already been stated that soil tightness i.e. retention of fines and permittivity are two contrasting functions. A judicious compromise has to be made in respect of selection of JGT so that both the functional demands are met. Survivability of JGT is important and therefore fabric should possess sufficient strength against installation stresses Design Approach a) Retention The basic relation is O n (usually O 90 or O 95 ) < d n (usually d 90 or d 50 ), where O n is the Apparent Opening size. If O n is increased then there is a possibility of piping i.e. sub-surface erosion. On the other hand, if O n is decreased, clogging may take place, causing differential over pressures across the JGT. The following recommendations may be followed in case of JGT as adopted by AASHTO (1990) in respect of synthetic geotextiles. AOS (apparent opening size i.e. O 95 ) should be less than 600 micron if d 50 is larger than mm. and AOS should be less than 300 microns if d 50 is less than mm. b) Permittivity Permittivity is the ratio of co-efficient of permeability of JGT (k g ) and its thickness (t g ). It should be ensured that the coefficient of permittivity of JGT (k g ) should be more than the coefficient of permeability of the soil (k s ). In other words, (k g ) >(k s ). In rivers having reversing flows, Kg should be at least 100 times Ks. As already mentioned, chances of both mechanical and chemical clogging of JGT cannot be ruled out. Clogging potential of JGT should be tested as per ASTM D 5101 (Gradient Ratio test), or any other suitable method (Hydraulic Conductivity Ratio test). A JGT is expected to function with a low probability of clogging when the flow rate initially decreases with time and then stabilizes to a certain value over a time period. Normally the Permittivity should be greater than 5 x 10 3 k s x i s where k s is the co-efficient of permeability of the base soil and is i s hydraulic gradient of soil. There is however a cautionary note : If there is a possibility of down slope migration of soil in the bank, JGT should be laid on a granular sub-base. Alternatively, JGT should be thicker than the normal design thickness either in a single layer or by combination (multiple layers) Installation : The bank should first be cut to a stable slope preferably at the angle of internal friction of the bank soil. The surface should be levelled and made free from angular projections, undulation, soil-slurry or mud. Anchoring trench (usually rectangular) should be excavated at the top of the slope. Recommended dimensions of the trench 500 mm deep and at least 250 mm wide at the bottom. The trench should be free from foreign material, mud etc.

33 JGT should then be unrolled across the trench and along the slope from top down to the lowest water-level. JGT should be stapled with U-shaped nails (usually 11 gauge) within the anchoring trench both at the sides and bottom at an interval of 150 mm along the length of the trench. There should be at least two staples both depth-wise and widthwise in each cross section. JGT should be laid with the overlapping in the direction of water flow. Care should always be taken to ensure that JGT does not suffer damage due to puncture, tear and similar operational stresses. The recommended overlap is 150 mm (minimum). The overlapped portion should be stapled at an interval of 75 mm. The anchoring trench should then be filled with stones/boulders for securing and protecting the JGT. Care should be taken to ensure that JGT touches the bank slope at all points (proper drapability). Armour overlay of stone/boulder should then be placed on the JGT carefully. It should be ensured that armour stones/boulders are not dropped on the JGT, but are carefully placed and properly arranged. A thin layer of sand as a cushion on top of the JGT is recommended to avoid puncture of the fabric by granular overlay. Similar care in laying should be taken when a combination of granular filter and JGT is used under reversing flow-conditions. There must be a beam at the toe of slope. This can be done by folding the JGT as per dimensions (usually 500mm diameter) with sand filling and duly stapled on the other side preferably at an interval of 75 mm. Alternatively, an angular trench may be dug at the toe and the JGT placed on it ensuring full contact with the soil, duly stapled at a spacing of 75 mm and ballasted. Care should be taken to see that the overlapping layer is not displaced during installation. Suitable grass seeds should then be spread on the treated bank. Alternatively, saplings of suitable plants may be planted at close intervals through the interstices of the overlay, taking care to place them into the bank soil. Installation should be completed preferably just before the monsoon to take advantage o the rains for quick germination of seeds Monitoring and Maintenance The treated bank should be kept under watch for at least one full season cycle. Frequent visits to sites during and after the rains or any natural calamity are necessary. Siltation is expected to take place after about a month which should cover up the granular overlay gradually. Maintenance involves, besides monitoring, re-arrangement, of the overlay, if displaced, in position. No part of JGT should be allowed atmospheric exposure due to displacement of the overlay. In all bank erosion control works, it is imperative that the longevity of JGT should be at least 4 to 5 years. The purpose is two-fold. First, to allow sufficient time for stable formation of filter cake. Secondly, to ensure growth of a dense vegetative cover for holding the base soil

34 naturally. The selected JGT should therefore be smeared with suitable rot-resistant chemicals or industrial grade bitumen. Care may be taken to ensure that such application of rot resistant chemical/bitumen does not affect the porometry of JGT beyond a tolerance limit of 25 per cent. Considering that there may be reduction in Open Area Ratio (OAR) as a result of application of rot resistant chemical/bitumen, it is recommended that pore size of any selected untreated JGT should be decided keeping in view the possible reduction in OAR after treatment. The JGT strength may be ascertained after one season cycle and the overall performance should be analysed Stability of Embankments for Highways Stability of embankments concerns stability of the soil-body as a whole, apart from the stability of the exposed slopes. Road and railway embankments are subjected to moving traffic, which develop dynamic stresses within them. Flood-control embankments are supposed to withstand lateral thrusts of rising water which may seep into the embankment body and enhance the moisture content within it. It is worthwhile noting that soil derive stability from their shear strength. The safe slope of an embankment depends on the shear strength of the fill. Noncohesive granular soil possesses high internal frictional resistance which helps develop increasing shear strength with the addition of load Soil in general hardly possesses any tensile strength. It behaves differently according to its composition, structure and other geo-technical properties. As a result, embankment constructed with soils prone to volumetric variations, suffer failure in the shape of vertical subsidence, lateral dispersion, down-slope migration, rotational slides, etc. The use of JGT for reinforcing the soil in the body of the embankment shall be based on the evaluation of improvement expected in regard to its stability because of such use. The improvement is a function not only of the fill-properties, but also of the JGT Design Approach Reference may be made to Koerner (1990) for a suitable method of analysis or other text-books on geo-synthetics, dealing with reinforced embankments. Generally, stability of the embankment subjected to moving loads may be ensured by JGT, which can perform the following functions effectively: Initial Reinforcement An earthen embankment when subjected to moving loads, develops stresses and strains which may lead to its failure if the permissible limits are exceeded. JGT when placed at appropriate levels within an earthen embankment can absorb these stresses and strains to a substantial extent at the initial stages and control failure of the embankment. Soil-JGT friction acts as medium of transference of stresses and strain JGT, when put to tension, strengthen the soilbody. JGT can directly reinforce an embankment only during its useful life-span (not more than 4 to 5 years after rot-resistant treatment). In fact, JGT may not serve the purpose of reinforcing an embankment fully or a long period, but can certainly perform the functions of filtration, separation

35 and drainage which, in turn, induce strength and stability to the embankment-structure as a whole Separation JGT separates the natural ground from the fill materials of an embankment and thus prevent their intermixing. If the base-soil is weak and compressible, the first embankment layer can retain its geo-technical characteristics better as a result of the separation Filtration When the first embankment layer is made of freely draining materials, JGT can ensure soiltightness while allowing passage of water Drainage JGT may serve as a draining layer (Transmissivity), as a drainage layer by itself, within its own thickness when there is no localised out-flow of water. Functions of separation, filtration and drainage in combination accelerate consolidation of the fill of the embankment by gradual riddance of water. The basic design criteria are similar to what has been stated under Section on Bank Protection in Rivers and Waterways, in so far as porometry and permittivity are concerned, it is imperative that both the grain size distribution and coefficient of permeability of the fill and also of the base soil are determined for choice of an appropriate JGT. Before construction of any new embankment, JGT treated with bitumen of suitable grade should be laid on the base soil. The will prevent intermixing of the base soil and the fill material. If the soil material has a high Plasticity Index (i.e., high consistency and hence, high order of compressibility), it is recommended that two to three layers of JGT treated with suitable rot resistant chemicals should be laid in successive layers above the prepared ground. There should be provisions for siderestraint if the soil material has low internal friction. When permeability of the fill material is less than 10-5 metre/sec, a combination of woven and non woven JGT is recommended. In addition, design measures for slope stability are also to be taken care off Installation The following sequence of construction is recommended: The surface of the base should be levelled and cleared of any foreign materials Treated JGT should be placed at the interface of the base-soil and bottom of the proposed embankment with the fill material and folded up to ⅛ th of the base width of the proposed embankment More fill materials should be laid at the edge The central portion is to be filled next The height of the embankments is to be raised Complete filling the central portion in stages The slopes should be protected as already indicated under the relevant section. Note: - The fill-material should not be an organic soil or have - Plasticity index (P) not more than 20 and Liquid Limit (LL) more than 40 when tested according to IS 2720 (Part 5).

36 - Filling behind abutments and wing wall of all structures should conform to IRC / MoRTH Specifications - The fill materials shall be laid in horizontal layers and compacted as per IRC/ MoRTH Specifications. - Backfilling should not be done in water. Water should be bailed out, mud scooped out and JGT laid on the prepared ground. It is recommended that granular material of maximum particle size of 75 mm and uniformity co-efficient (d 60 /d 10 ) above 10 should be used in such cases as fill material. - Sufficient settlement period should be allowed to the new embankment before any construction is undertaken. Alternatively, methodology of pre-loading the new embankment maybe considered. - In case of very high embankments, treated JGT may interposted at appropriate layers within the embankment body; however, a separate design should be obtained from an expert Monitoring Any newly constructed embankment should be monitored for two season cycles for settlement and other distresses. The basic principles for a trouble free stable embankment is to avoid ingress of water into it and to draw out water if there be any entrapped water/moisture within it Strengthening of Pavement Structure in Roads Poor subgrade often causes pavement-failures as strains accumulate under repeated dynamic loads of traffic. It often happens that the materials in the base course of the pavement get intermixed with the subgrade, reducing the required depth of the pavement decided on the basis of class of loading vis-à-vis CBR (California Bearing Ratio). A poor subgrade may also cause lateral displacement of the subgrade and the base-materials under loads. Insufficient drainage of the surface water and also the entrapped moisture/water within the sub-surface layers along with the seepage of water from the sides often lead to road-failures. JGT can tackle all these problems effectively by segregating different layers of a road pavement, preventing movement of the subgrade soil (soil tightness) and facilitating filtration through them Design Approach JGT when placed over the subgrade help stabilize it in a number of ways. Besides preventing intermixing of the subgrade and the sub-base, JGT also check the upward movement of the fine particles in the subgrade, provide frictional resistance against lateral dispersion and act as a support membrane It is always advisable to segregate the soft subgrade from the pavement layers by selecting a proper JGT-fabric with the right strength, porometry and permittivity. JGT to be used in road should have a Puncture Strength of 400 N and a tensile strength of at least kn/metre. Normally the available woven geotextile meet the above strength requirement. Porometry of the JGT may be decided on the basis of mean grain size of the subgrade as

37 already indicated in preceding sections. Permittivity of the JGT depends on the permeability of the subgrade and may be determined as per recommendations given. Subgrade has to be compacted to optimum moisture content (OMC) prior to laying of the selected JGT Installation The subgrade is to be excavated to the required level, cleared of all foreign materials and compacted to the OMC (Optimum Moisture Content). The subgrade should be done up with the specified profile. Vegetation, if any, should be uprooted and the area levelled with earth and rolled. JGT as selected should be laid by unrolling, ensuring proper drapability (i.e., JGT should touch the subgrade surface at all points) and stapled at an interval of 300 mm with overlaps of 150 mm. Staples should be preferably U-shaped nails (11 gauge). It is preferable to avoid overlaps to the extent possible. A thin cushion of local sand (minimum 15 mm thick) may be spread over the JGT to prevent puncture/damage due to rolling of the upper sub-base/base-layer. The first layer of aggregates in the Sub-base layer (conforming to IRC/ MoRTH specifications) should then be spread. No traffic should be allowed on an un-compacted base with less than 200 mm (150 mm for CBR>3) thickness laid over JGT. Any rut that may develop during construction should be filled in. Parallel rolls of JGT should be overlapped and stapled. For application in curves, JGT should be folded or cut and overlapped in the direction of the turn. Folds in JGT should be stapled at an interval of 300 mm. Before covering up the JGT, its condition should be assessed for any constructional/installation damage. Torn/damaged portions may be covered by pieces of JGT and duly stapled on all sides preferably at an interval of 75 mm. The extent of overlap will be such as to fully cover the damaged/torn portion fully plus at least 75 mm beyond, on all sides. Usually filling is carried upto a height of 1.5 m after placing of JGT as first stage during stage wise construction of road embankment. Sufficient waiting period as per design needs to be provided for consolidation process to take place Shoulder Drainage Often the sub-surface water is drained through the JGT-medium to the shoulders of a carriage way. In such cases, shoulder drains are required to be constructed either beneath the edge of the shoulder or immediately adjacent to its edge (In USA, such drains are called under-drains ). In the event of existence of black cotton soil or expansive clay, porous drain pipes are also inserted within the shoulder drain to augment drainage efficiency Monitoring and Maintenance The performance of the pavement with JGT should be monitored closely, especially with regard to development of pot holes, subsidence, road side drainage, dispersion of subgrade and the like. Frequency and extent of surface treatment and also re-sectioning needed are also to be

38 noted. Special attention is necessary during and after the rains. Pot holes should be immediately restored. Surface drainage over the pavement should not be allowed to hinder due to malfunctioning of road side and shoulder drains. Close monitoring should be done at least for two season cycles by noting the type and extent of subsidence of tracks. Clogging of the drainage outlet requires surveillance. Review of design (depth and spacing of JGT fibre drains) may have to be done in case erosion pumping failure persists Consolidation of Soft Soil Compressible soils pose problems for any type of construction on it due to their volume variation with change in water-content. Consolidation of soil can be achieved if the water in the sub-surface layers can be drained out. In order to drain out water quickly from the saturated subsoil, sand/band drains/sand-wicks are conventionally being used. Band drains are made up of synthetic fibres. Instead of synthetic fibres, jute fibres can also be used to manufacture band drains. The Indian Jute Industries Research Association has developed prefabricated JGT drains. JGT fibre drains have been successfully used to accelerate consolidation of subsoil. Pre-fabricated JGT fibre drains can act as an extremely effective draining medium. Sand-wicks are essentially porous stockings filled with sand. JGT fibre drains have been developed with jute-wicks inside instead of sand Specification of prefabricated JGT drain The specifications of Prefabricated JGT drains developed by IJIRA (with the guidance of Prof. Ramaswamy) are indicated below. The properties are : Weight/metre 140 gm Tensile strength 4.5 kn Extension 4 to 5 per cent Permeability at 50 mm water head 0.41 mm/sec Discharge capability at 50 kpa under unit hydraulic gradient 13.1 ml/sec Design approach The design approach is similar to what is normally being used for geosynthetic drains. The general steps in designing band drains is indicated below. However, it is suggested that an expert opinion be taken for designing and installation of jute geotextile band drains for consolidation of soft subsoils Installation of prefabricated Jute drains Special drilling equipments are needed for digging deep holes and removing the loose spoils. JGT fibre drain should be guided into the drilled holes by mechanical or suitable contrivances and the annular spaces filled up with sand. Indian Institute of Technology (IIT), Delhi has developed a special machine for this purpose. The details of the same are available at Textile Engineering and Civil Engineering Department of IIT, Delhi. Some general steps of installation are indicated below.

39 Drilling of holes (diameter 150 mm for 100 mm wide prefabricated jute drains) with augers usually 2 metres below the bottom ballast level. Taking out of all loose materials from the holes. Insertion of JGT prefab drains inside the holes with help of split bamboo sticks, taking care to place it centrally. Filling the side-space with sand/non-cohesive fine aggregates. The top of the JGT drains should be kept slightly above the bottom ballast level of the track. If there is a sand blanket under the ballast, the top of the fibre drains can be kept under the sand blanket. In case of JGT-wrapped porous pipes to be laid laterally, horizontal drilling may have to be done, loose materials removed and the pipe inserted keeping their outfall end laid on to the exposed surface of the embankment slope for ultimate drainage of the entrapped water Monitoring Monitoring should be done at regular intervals for noting the rate of consolidation and settlement. One season-cycle is usually adequate for full consolidation Jute Geotextile for Controlling Reflection Cracks in Roads Life of a flexible pavement depends basically on its flexural strength. Usually, except in cases of subgrade failure, flexural fatigue and also natural ageing may cause cracks to develop and propagate within a flexible pavement. Crack propagation can be stalled by interposing a fabric in combination within the existing pavement. Jute Geotextile (JGT) has been used to act as the interposing fabric to prevent cracks from getting propagated in the upper layer of a bituminous pavement Reflection cracks occur after re-surfacing of a cracked road. Thermal changes usually tend to induce a tensile force in the horizontal direction. Repetitive vehicular loads induce vertical shear. Combination of the two causes parallel shear to develop. Understandably, the crack(s) on the pavement-base are the line(s) of weakness on either side of which there is interplay of fluctuating stresses. Crack(s) once formed want to move up and result in a line of cleavage in the riding surface Synthetic Geotextiles have been successfully used in some parts of the world to delay the propagation of reflection cracks in both bituminous as well as rigid pavements. Jute Geotextile (JGT) instead of synthetic one, is also one of the viable options for use as a reflection crack arresting layer. JGT is to be laid on an old bituminous pavement after sealing the existing cracks with neat bitumen. JGT may be laid with a tack coat of bitumen followed by a premixed sheet of bitumen stone chip stone dust mix. The grade of bitumen should be decided on the basis of site conditions and ambient temperature. Modified rubberised bitumen may also be tried. Jute and bitumen have excellent thermal compatibility. Bitumen heated up to 190 o C may be safely used.

40 The quantity of tack coat should depend on the nature of surface of the pavement base. Normally, bitumen at the rate of 0.3 kg/m 2 may be used as tack coat overlain by another coat of bitumen of the same quantity. Woven JGT to be used should be capable of withstanding tensile stress to the extent of 30 kn/metre initially in both machine and cross-directions. JGT having a porometry of 70 per cent coverage (open area of about 30per cent) should serve the purpose. The specifications are provisional and are subject to alteration in accordance with the site conditions New Areas of Application of JGT Besides the areas mentioned in the preceding chapters, several new areas of application deserve consideration for laboratory investigation and field trial. The following areas may open up new end-uses of JGT In bituminous overlays Bituminous overlays are used as wearing course over exiting black top pavements. Bitumen impregnated geotextile may be laid between the top bituminous macadam layer and the bituminous wearing overlay. This may enhance the service life of the wearing course. Bitumen and jute have excellent thermal compatibility. JGT may also help in prevention of reflective cracking In temporary haul roads JGT can provide the desired reinforcing effects in temporary haul roads which are required to be constructed for access to sites for a limited period. Its initial stiffness and low extensibility may be effective in temporary high-duty roads As fabriforms Fabriforms are used to mould wet concrete in a desired shape. JGT may be cut and stitched in accordance with the desired shape of concrete before being filled up with wet concrete. Fabriforms made of jute geotextiles may be put to use for making revetment mattresses and remedial works for concrete structure. The function of JGT is to give and retain the desired shape of the concrete and its function ceases once the concrete hardens. Biodegradability of JGT is an advantage in such cases Jute Geo Cell Use of jute geocells in low cost embankments and pavements construction on soft soil has been advocated by Mandal and Mhaiskar (1994). For design of low cost embankments with jute geocells, Mandal et al have recommended use of slip line theory (by H. Hency 1923) and for designing pavement on soft soils, the method proposed by AASHO (American Association of State Highway Officials). Jute Geocells are innovative forms of JGT and are worth trying in the aforesaid areas.

41 12. Cost of Jute Geotextiles and Commercialisation 12.1 The comparative cost of natural jute geotextiles and synthetic geotextiles is shown in Table 10. It is observed that open mesh JGT is around four times cheaper than similar SGT while the woven JGT is about half the cost of SGT. The non woven JGT is more than five times cheaper than the synthetic non woven. The cost data provided in the Table 10 is based on a survey carried out by the authors in the year The costs are only indicative and subject price variation and escalation. The readers are advised to contact the manufacturers whose addresses are provided in the document. Table 10: Comparative cost of Jute Geotextiles (JGT) & Synthetic geotextiles(sgt) A. Open mesh JGT (exfactory) Open mesh SGT Rs.7.00 to Rs per m 2 Rs per m2 (not usually used) B. Woven JGT (ex-factory) Woven SGT Rs to Rs per m 2 Rs to Rs per m 2 C. Non woven JGT (ex-factory) Non woven SGT Rs.9.00 to Rs per m 2 Rs to Rs per m Since mid eighties large scale experimental trials followed by commercialisation of JGT in different application areas have established the efficacy of the product. It has also been established that biodegradability of jute has got no detrimental effects on its demand. Table 11 shows the domestic consumption of JGT during the year 2000 and Table 11: Comparative Consumption of JGT during 2000 and 2001 in India Sector Area (m 2 ) Weight (MT) Area (m 2 ) Weight (MT) Irrigation & Waterways (760 gsm treated) 20, ,15, PWD (Roads) (760 gsm grey & 300 gsm grey) 28, , Mines (500 gsm) - - 1,30, Railways (760 gsm treated, 500 gsm grey & 500 gsm non woven) 15, , Total 63, ,84, Note: Export figures have not been shown

42 13. Laboratories Studies on Jute Geotextiles 13.1 Several laboratory investigations were carried out to assess the Feasibility of using jute geotextiles for different applications in the laboratory scale. Some of the laboratory investigations carried out on the jute applications are given below Jute Geotextiles for Roads Laboratory Investigations Objectives of the study i) To assess the feasibility of using jute geotextiles for application in road construction ii) To observe whether the biodegradability of jute fabric is a deterrent factor for its use as a separator in road construction Laboratory Investigations Extensive studies were carried out to evaluate behaviour of jute fabric under different types of loading conditions Dynamic Load Test Dynamic load test was conducted with clayey subgrade at 40 per cent moisture content. A dynamic load of 8 kn and a simulated contact pressure of 255 kn/m 2 was applied. Upto 1000 load applications were made. The results of the dynamic load test are presented in Fig 6 and also in Table 12. Table 12: Results of Dynamic Load test on Jute geotextile Thickness of Rut Depth (mm) Remarks aggregate layer (mm) Without JGT With JGT With the use of JGT, more than 50 per cent reduction in rut depth in both cases The results of the dynamic load tests on jute fabric correlate very well with those of Lai and Robnett who carried out similar tests on a synthetic geotextile (Ref: Lai, J.A.S and Robnett, Q.L (1980), Designing and use of geotextiles in road construction, Proceedings of third Conference of Road Engineering Association of Asia and Australia, Taipei) Static Load Tests Static load test was conducted on clay in layers of 100 mm. Jute fabric was placed with back filling of 100 mm thick moist sand (Moisture content 6 per cent) and pavement pressure of 2.4 kn/m 2 was simulated. Short time rutting tests were performed under a series of loading pressures from simulated wheel loads of 350 N, 900 N and 1350 N, while long term (6 weeks) loading tests were performed under simulated wheel loads of about 1000 N on bearing plate of 200 mm diameter. Results of short term static load tests and long term sustained loading tests were found satisfactory and are presented in Fig 7 and Unconfined Compressive Strength and CBR Test Unconfined compressive strength and CBR tests were carried out to assess the influence of jute geotextile on the strength of clayey subgrade at different moisture contents. The findings are presented in Table 13 and 14.

43 Table 13: Effect of Jute Geotextile on Unconfined Compressive Strength Water Unconfined Compressive Strength (kn/m 2 ) Strain at failure (%) Content (%) Without Fabric With Fabric Without Fabric With Fabric Table 14: Effect of Jute Geotextile on Laboratory CBR Values Water Content (%) Without Fabric CBR Value (%) With Fabric In-situ Trials Plate load test was conducted to evaluate the in-situ behaviour of the subgrade soils provided with JGT. The subgrade soil used was soft to medium silty clay having natural moisture content equal to 35 per cent and Vane shear strength (in-situ) equal to 20 kn/m 2. Plates of 300 mm diameter were used. The results are similar to tests reported with man made geotextiles (Ref: Jerret, P.M., et al (1997), The use of Fabrics in Road Construction on Peat, International Conference on Soil Textiles, Paris, France, pp 19 22) Durability Tests The test specimens consisted of JGT treated with 40 per cent, 50 per cent and 60 per cent bitumen and samples were preserved with 3.5 per cent, 6 per cent and 12 per cent preservative. They were kept in different environment like acidic solution (ph = 3), alkaline solution (ph = 12) or buried under clay in a separate container and the grab tensile strength test was performed after every month upto one year. Durability studies confirmed that the JGT retains sufficient strength for about one year Conclusion Jute geotextiles function in a manner similar to their synthetic counterpart. The laboratory tests confirmed that application of JGT significantly improves bearing capacity and settlement behaviour of reinforced with JGT. JGT were found durable upto one year when treated with bitumen and other preservatives.

44 Fig 6: Typical surface rut depth vs number of load application for dynamic load test using jute geotextile Fig 7: Load settlement relationship with and without jute geotextile

45 Fig 8: Rut time relationship for sustained seven weeks loading test 13.3 Comparative study of Synthetic and Jute Geotextile for Erosion Control This laboratory study was taken up to evaluate performance of JGT for surfacial erosion control and to assess the comparative performance of such systems made with synthetic geotextiles vis-à-vis JGT. An artificial embankment slope constructed beneath a rainfall simulator was used for the experiment. The embankment slope modelled by battered face of the soil was inclined at 26 0 to the horizontal to represent a 1V:2H slope. The slope width of 5 m was divided into 6 trial bays, each 500 m wide to allow space between adjacent bays. To conduct the experiment, Simulated rainfall was generated using a series of nozzles fixed to an oscillating bar above the slope. Rainfall drop size was kept equal to 1.3 mm Kinetic energy of rainfall was 14 joules/ m 2 / mm Eight storms were simulated, each having return period of 100 years for Eastern England region First five storms had rainfall intensity of 40 mm/hour with one hour duration. The first storm was on a pre-wetted slope. The remaining four storms at this intensity were run in pairs at three day intervals such that the first storm of each pair fall on a dry slope. Two hours duration was allowed for drainage before starting the second cycle on a wet slope. After a three day drying the same cycle was repeated.

46 A different approach was adopted for the last three storms. Rainfall intensity was increased to 75 mm/hour and the storm duration was decreased to 20 minutes. The first cycle comprised one storm falling on a dry slope and after two hours, a second storm was applied on a wet slope. After three day period, the slope was pre-wetted and a single storm was applied to the wet slope. Each of the five samples were installed on 500 mm x 1.8 m trial plot in accordance with the supplier s instructions The sixth plot was top seeded in a usual manner and used as a control plot. All the six plots were seeded to assess the ability of each product to resist washout of the un-germinated seed. The control plot and other five plots were covered with 200 mm top soil comprising of 12 per cent clay, 29 per cent silt, 33 per cent sand and 26 per cent gravel. Seeding was done by hand using commercially available grass seeds at the rate of 28 gm/m 2. Table 15: Type and Characteristics of Fabrics Selected for Trials Geotextile Composition Properties Weight (gm/ m 2 ) Thickness (mm) Tensile Strength Opening Size (mm x Durability (Years) (kn/m) mm)) JGT Jute x 18 2 Commercial Wood / Wool x synthetic mat 1 (CSM 1) mulch contained in PP strand mesh Commercial Polyamide synthetic mat 2 (CSM 2) Commercial Polyethylene x 8 - synthetic mat 3 (CSM 3) Commercial synthetic mat 4 (CSM 4) HDPE Results Some inconsistent and very low run-off values were obtained for the initial application of 40 mm/hour intensity storm to the pre-wetted slope due to high initial rates of filtration. Similar problems were encountered for dry slope at the higher intensity of rainfall. These results were disregarded when calculating mean run-off values, there by leaving reliable data for wet slopes only at 75 mm/hour rainfall intensity. The run-off values obtained are presented in Table 16.

47 Table 16: Run-off (in cc) in Different Test Beds System Dry Slope, Rainfall 40 mm/hr Wet Slope, Rainfall 40 mm/hr Wet Slope, Rainfall 75 mm/hr Control Section JGT CSM CSM CSM CSM Storm Duration One Hour One Hour 20 Mins The relative effect of different rainfall intensities, where sediment loss is expressed in grams are shown in Table 17. During this test, storm duration was normalised in all the three cases to one hour. Table 17: Sediment Loss (in Grams) in Different Test Beds System Dry Slope, Rainfall 40 mm/hr Wet Slope, Rainfall 40 mm/hr Wet Slope, Rainfall 75 mm/hr Control Section JGT CSM CSM CSM CSM Mean values of soil erodibility (gm/mm) are given in Table 18. Table 18: Soil Erodibility (in gm/mm) in Different Test Beds System Dry Slope, Rainfall 40 Wet Slope, Rainfall 40 Wet Slope, Rainfall 75 Overall Average mm/hr mm/hr mm/hr Control Section JGT CSM CSM CSM CSM Storm Duration One Hour One Hour 20 Mins

48 Moisture absorption of different systems expressed in percentage of original dry weight is given below in Table 19. Table 19: Moisture Absorption (as percentage of dry weight) in Different Test Beds System Absorbed Moisture JGT 485 CSM 1 Not Measured CSM CSM 3 40 CSM 4 9 The results clearly showed that JGT is very effective in reducing erosion of the soil beds. All the products tested reduced erosion, where as JGT proved to be most effective at higher intensity of rainfall. JGT reduced erosion under lower rainfall unprotected soil (initially dry condition) and to 27 per cent of unprotected soil (initially wet condition). JGT seems to operate mainly through considerable reduction in run-off. JGT is the most effective product for containing erosion due to higher intensity rain and also showed a tendency to become more effective with time. This is due to better drapability of JGT when it is wet which helps to maintain close contact between JGT and the soil surface Use of Jute Geotextiles for Construction of Roads for Light Traffic A laboratory Experiment This experimental study was taken up to ascertain improvement in load bearing capacity of subgrade soil with the introduction of JGT and two layers of bricks. Six sets of plate load tests were conducted with mm thick steel plate of 30cm X 30cm deep. The plate was placed centrally into the test pit of size 150cm X 150cm and 30 cm deep. The conventional method was followed for the plate load test. The schedules of the tests are given below in Table 20. Table 20: Test Details for Use of JGT in Light Traffic Roads Test Set The Test Pit Layers of brick laid over the final level (a) 30cms No brick Layer (b) 60cm; made 30cms by filling with same virgin soil One layer of brick (c) 60cm; made 30cms by filling with same virgin soil No brick layer over JGT (60cms x 60cms) (d) Same as in set (c) One layer of brick (e) Same as in set (b) Two layer of brick (f) JGT(60cms x 60cms) was placed at 60 cms depth and 30cms depth was made by placing virgin soil over JGT Two layer of brick (The experimental study was made by Dr. Amalendu Ghosh, Prof.,Civil Engineering Deptt, B.E college, West Bengal, India; Published in All India Seminar on Application of Jute Geotextile in Civil Engineering: (March 07,2002)

49 Characteristics of Soil Used The soil used on the test was silty clay having properties given in Table 21. Table 21: Properties of Soil Used in the Experiment Property Value Liquid Limit 78 Per Cent Plastic Limit 40 Per Cent Natural Moisture Content 30 Per Cent Unconfined Compressive strength 4.7 t /m 2 Procter Test - OMC 21 Per cent Procter Test - Max Dry density 1.57 gm/ cc Result of Plate Load Tests The yield stresses and corresponding settlements for different cases are given below in Table 22. Table 22: Results of the Plate Load Tests Type of test medium Yield stress, t/m 2 Settlement, mm Virgin soil (set a) Compacted soil* underlain by single Layer of brick (set b) Compacted soil underlain by one layer of jute-textile (set c) Compacted soil overlain by By single layer of bricks and underlain By a layer of jute geo-textile (set d) Compacted soil overlain by two layers of brick (set e) Compacted soil overlain by two layers of bricks and underlain by a layer of jute geo-textile (set f) *compacted soil was obtained in the pit near OMC at the unconfined compressive strength of the compacted fill of 6.6 t/m Characteristics of Jute Geotextile Used Weight 418 gm/m 2 Thickness Tensile strength In-plane permeability Cross plane permeability Conclusions mm Kg/cm x 10-3 cm/sec 1.358x 10-3 cm/sec Placement on the layer of bricks on the top of the surface of compacted soil set (b) helps for increasing the load Carrying capacity quite significantly compared to virgin soil, set (a) or simple a jute geo-textile layer overlain by compacted soil set (c) The response of two layers of bricks over compacted soil (set e) has been better. But when one brick layer along with a jute geo textile layer (set d), the load carrying capacity is improved and is higher than that in the case when only two layers of bricks are used (set e).

50 The best results is obtained when two layers of bricks are used in addition to layer of jute geo-textile (set f) but (set d) appears to be most effective both from performance and economic point of view in case of two low volume rural road construction. Repeated Load Tests on Jute Geotextile and Bamboo Reinforcement Repeated (Cyclic) load tests were conducted to compare the behaviour of unreinforced and jute geotextile and bamboo reinforced unpaved roads. These tests were aimed to ascertain the effectiveness of reinforcement in increasing the fatigue resistance of the pavement structure. The cyclic test was carried out on a 16 cm thick gravel sub-base layer loaded directly over soft subgrades; Gravel subbase layer with jute geotextile at the subbase-subgrade interface and Gravel subbase layer with jute geotextile and a bamboo grid at subbase-subgrade interface. Test Set up The loading frame procedure for compacting the subgrade (Bombay marine clay) and subbase (Byhatti gravely soil) was the same as that in the static loading test. The hydraulic jack was replaced by a pneumatic cylinder which had a 75 mm ram movement. The ram movement the period and the applied force was controlled by a specially designed setup consisting of a pressure regulator, Solenoid values, etc. Testing Procedure Three repetitive loading tests were performed on unpaved road model. Since, this was an unpaved road, the number of load applications were limited to 10,000 cycles. The pavement was subjected to a cyclic pressure of 197 k Pa (maximum) application. Seven cycles were applied in a minute to simulate the traffic condition on an unpaved road. Resutls and Discussions Fig. 9 to 12 shows the fatigue behaviour of un-reinforced and reinforced subgrade upto 10,000 cycles of load application. It is observed from Fig 9 to 12, that with increase in number of cycles of load application, the fatigue resistance decreases as a result of which deformations of the pavement increase. This is particularly observed when the pavement is subjected to large number of load application. The effectiveness of the reinforcement in reducing the fatigue is measured by considering the cumulative deformation of the pavement after 10,000 cycles of load applications (Table 23). It was found that jute geotextile and bamboo grid at the subbase-subgrade interface was the most effective of arrangement of reinforcement for reduction in pavement deformation. Providing only a jute geotextile as a reinforcement also increased the fatigue resistance type of test. Table 23: Reduction in the Pavement Deformation due to Reinforcement Type of Test Cumulative Deformation of the pavement (mm) Per cent Reduction in Deformation of the pavement Unreinforced pavement Jute geotextile reinforced Jute and Bamboo grid reinforced pavement

51 Fig. 9: Cumulative Deformation Vs. No. of cycles for unreinforced and reinforced pavements Fig. 10: Cumulative Deformation Vs. No. of cycles for unreinforced and reinforced pavements

52 Fig. 11: Cumulative deformation Vs. No. of cycles for unreinforced and reinforced pavements Fig. 12: Cumulative deformation Vs. No. of cycles for unreinforced and reinforced pavements

53 14. Some Case Histories/ Field demonstration To promote use of jute geotextiles in civil engineering applications, a series of field experiments were carried out using jute geotextiles for different functions. Application of jute geotextiles for different functions at different locations are described in the following sections Jute Geotextiles as Separator Roads around Kandla Port In Kandla port area, authorities were facing the problem of road construction on soft soil. The road network in the Kandla port trust area was to be improved to facilitate better movement of vehicular traffic. The soil in the port area is very soft and has very low bearing capacity, premature failure of road pavements were a common occurrence in the area. In order to improve the pavement performance, it was suggested that a layer of geotextile be provided over the soft subgrade to prevent the intermixing of subgrade and subbase soil. In the broad spectrum of geotextiles, natural geotextiles made of jute are very helpful. They are eco-friendly, economical and at the same time serve the desired function. It was proposed to use jute geotextile as a separator between pavement layers. The performance of pavements constructed on soft soils can be improved using jute geotextiles. The jute fabric as separator was provided with a view to prevent the penetration of subgrade material into voids of granular base course, for faster dissipation of pore pressures and ensures better drainage, which result in long term performance of the pavement. It was also expected that provision of fabric would reduce rutting and subgrade would develop its full bearing capacity. The properties of jute geotextile used in the experimental trial are given in Table 25. Table 25: Properties of jute geotextile used as a separator at Kandla Port Sl. Description of Property Value No. 1 Type Woven 2 Tensile strength kn/m 3 Thickness 6.91 mm 4 CBR push through load 0.5 kn 5 Index puncture resistance kn 6 Inplane permeability 9.2 x 10-4 m/s 7 Falling cone test No clear hole formed 8 Failure strain 30 per cent The table shows that the fabric has low tensile strength but fails at a large strain of the order of 30 per cent. In particular, in falling cone test, no clear depression or punching was observed under the fall of the cone indicating the resistance of fabric for puncturing with aggregate or the material used in base layers. Design The geotextile can provide restraint and acts as reinforcement and prevent localized bearing capacity failures, which result from individual stones being forced into the subgrade. The pressure at the stone/geotextile interface is related to the burst pressure for a given aggregate

54 size. A design guide for separator function indicating the requirement of burst resistance was developed for the field application. Construction Details Site was cleaned properly from its rough surface. Spreading and compaction of moorum cushion was carried out subsequently. The area was instrumented by installation of settlement gauges. Fig 13: Treated stretch of embankment (Kandla Port) Fig 14: Untreated stretch of embankment damaged after cyclone at Kandla

55 The subgrade was compacted to the optimum water content and maximum dry density of the subgrade material. The jute geotextile was spread over the compacted subgrade. This corresponds to the requirement of the low bursting strength of geotextile and also helps in reducing the impact of large sized aggregates. A thin layer of morum with average thickness of about 10 mm was provided at the interface to prevent punching of jute geotextile by large size aggregates. It was followed by the base course consisting of two WBM layers of 300 mm thickness of mm size aggregates followed by a 200 mm thick WBM constructed using 40 to 60 mm size aggregates. Monitoring of the completed section The engineers of Kandla Port Trust monitored the completed section for its performance in terms of rut depth and other visible signs of distress. Settlements of the test section in relation to conventional pavement section were being monitored. Settlement of the test section in relation to conventional pavement section was recorded with the increase of pavement loads from 0.5 MT/sq. m to 2.0 MT/sq. m. Loads were increased in increments of 0.5 MT/sq. m each month from February 1997 to May Results of the settlements recorded from February 97 to May 97 sent by Kandla port trust, shows almost negligible settlements after six months and no signs of distress in the treated test section. During the cyclone of Oct. 1996, the untreated stretch got badly damaged, however, the treated stretch was not affected. This encouraging result had prompted the Kandla port trust to purchase another consignment of 15,000 sq. m of Jute geotextiles from IJMA, which has been used for road and embankment construction in creep area in Kandla port. Some photographs showing the site and laying of geotextile is shown in Fig 13 and Guptipara Station Road in the district of Hooghly, West Bengal Construction of pavement of Guptipara Station Road using JGT was taken up as a demonstration project since it was having a good volume of traffic. The objective was to reduce the designed thickness of the pavement by introducing jute Geotextiles. The 300 GSM 200 SD jute non woven was selected to conduct the field trial. The original designed thickness of pavement was 450 mm but in the trial the pavement thickness was reduced to 400 mm. Horizontal drainage system was introduced by laying 50 cm wide jute non woven at both sides of the road at a depth of 4000mm under compacted soil and broken brick bats. The work was conducted during May-June, The work was kept under continuous observation and performances were monitored. The performance of the stretch of the road treated with JGT was good for a considerable period whereas the stretch without JGT showed signs of deterioration in the form of ruts, potholes and cracking on the surface though the thickness of the untreated pavement was 50 mm more than the JGT laid stretch. Hence it can be inferred that the JGT has performed significantly to contribute better towards durability of the road.

56 Widening and Strengthening of Munshirhat Pero-Khila Rajapur Road in the district of Howrah, West Bengal The road was taken up for improvement and widening under RIDF-IV Scheme. The original road pavement was 3 m wide and there were proposals for widening it to 5.5m. The total length of the road was 11.3 km, out of which widening portion of 2km was selected for treatment with JGT for strengthening. The road passes through low-lying area with high water table and poor soil belt. The JGT installed on the extended portion of the road on both sides after compaction of the subgrade. Over the JGT brick bats, Jhama metal and stone metal consolidation were done. The B.M with premixed carpet and seal coat was extended throughout 5.5 m width of the road. The properties of JGT used in this road are given in Table 25. Table 25: Properties of JGT (Rot Proof) Used at Munshirhat Pero-Khila Rajapur Road Property Value Weight (gm/m 2 ) at 20 per cent moisture content 760 Threads / dm (MD x CD) 102 x 39 Thickness (mm) 2 Width (mm) 76 Strength (kn/m) (MD x CD) 20 x 20 Elongation at break (%) (MD x CD) 10 x 10 Pore sixe (O 90 ) micron 300 Water permittivity at 10 cm water head (litre/m 2 /sec) 50 Puncture resistance (N/cm 2 ) 380 The road was constructed in the year 2000 and was kept under constant observations under the offices of Howrah Highway Division, PW (Roads) Department. They evaluated the performances of the portion treated with JGT and compared with untreated stretches. The widening portion without having JGT showed signs of distress and formed depressions and pot holes whereas the portion treated with JGT is much better and showed very little or negligible distress even after a lapse of three monsoons Rehabilitation of Roads The following roads under Serampore Municipality, West Bengal were rehabilitated using jute geotextiles. a. Road in front of Serampore Municipality and Railway level Crossing (Medium traffic) b. Netaji Subhas Avenue (High traffic volume) c. Thakur Das Babu lane, in front of Bandav Samity (Low traffic volume) All the above roads had continuously suffered from early distresses and required frequent repairs and rehabilitation. To solve the perpetual problem rehabilitation work was done applying Jute- Geotextiles and their performance have been kept under rigid monitoring and regular inspection. The work was completed before the advent of monsoon in the year Almost couple of monsoons have already been elapsed there is practically no appreciable signs of distress was observed. The riding quality of the above roads surfaces is good. improvement of performance level due to use of JGT in repairing work. This indicates the

57 14.2. Jute Geotextiles as Initial Reinforcement To Support Embankments at Kakinada A deep-water port was under construction at Kakinada in Andhra Pradesh and within the port area a number of highway embankments were under construction for transporting cargo from the ships to the storage godowns. At some locations, the subsoil was soft silty clay and the water table was at 0.5m below the ground level. The whole area was getting submerged during high tide (Fig 23). The highway constructed earlier faced many problems during and after construction such as subsidence of the fill during construction, excessive post construction settlements and lateral spreading of fill material etc. On the basis of settlement calculations, it was estimated that as much as 30 per cent of the fill would sink into the soft subsoil during spreading of the fill itself, necessitating extra quantities of costly granular fill material, thereby, pushing up the cost of construction. In order to mitigate the above problems, various alternatives were examined, among which geotextile was found to be the promising one. The use of jute geotextile to improve embankments over soft subsoil was proposed as it is an effective method for reinforced soil construction. Geotextiles was proposed be used to improve i) the embankment stability against bearing capacity failure, ii) stability against slope failure through the foundation, iii) allow a more controlled construction over very soft or difficult foundation soils, iv) ensure more uniform settlement of the embankment and v) to also act as separator between the embankment material and soft sub soil. They also performed as drainage blanket for draining pore water during consolidation. Embankment stability usually needs to be improved only during the short period in which the foundation consolidates, and in such cases the long-term durability of the geotextile reinforcement is of secondary concern. Reinforcement in an embankment on soft soil is very effective when placed at or close to the foundation surface. If the reinforcement were absent, the factor of safety at the end of construction would fall to a value below unity. In other words, the desired cross section cannot be built without the reinforcement. Again the factor of safety starts increasing, as the strength of the foundation soil improves due to consolidation and the foundation soil attains the required strength. Thus the reinforcement is needed only to improve the stability during construction and in that period of consolidation during which the soil attains the required strength. Fig 15 and 16 show the construction of embankment using JGT as initial reinforcement at Kakinada.

58 Fig 15: Embankment Construction Using Jute Geotextiles Kakinada Fig 16:Jute Geotextiles as Initial Reinforcement Kakinada

59 The main loading from an embankment is due to the vertical self-weight of the embankment fill, which causes horizontal stress in the fill, which in turn produces lateral forces (outward shear stress). The resulting outward shear stress, which acts on the foundation surface, reduces the foundation bearing capacity. So the primary role of reinforcement is to support the outward shear stress and relieve the foundation from the lateral forces, thereby, increasing the allowable height of the embankment that can be supported by the foundation soil. A layer of reinforcement placed in the embankment may resist lateral displacement by exerting an inward shear stress on the foundation surface thus reducing the lateral spreading of the foundation. Since the geotextile was placed between the embankment fill and the subsoil, it also performed the function of separator, thereby, eliminating the mixing of costly granular fill material with the subsoil. The geotextile along with the sand cushion will also act as a drainage layer for the escape of the pore water during consolidation. A woven jute geotextile was used for reinforcement and also as a separator between the embankment and the soft subsoil. From the experiment it was found that the required strength of the subsoil developed within the short life of the jute geotextile, which is biodegradable and degrades in about 2 years and is economical as well as safe to use geotextile in such projects. Design aspects While considering an embankment placed upon very soft soil foundation and supported by geotextile the following design elements were checked for arriving at the required properties of the geotextile. Bearing capacity: In order to check for bearing capacity failure and to check the geometry of embankment can be arrived at using the following considerations. q all = C Nc /FS q all = Y.H all where q all = Allowable bearing capacity Ý = Unit weight of the embankment soil H all = Allowable height of the embankment Nc = Bearing capacity factor C = Undrained shear strength of the foundation soil FS = Factor of safety From the above equations we can calculate the allowable height of the fill. Global stability: It is necessary to check the stability against slope failure passing through the foundation cutting across the geotextile, thereby, arriving at the required strength design of geotextile in major and minor principal stress direction. Elastic deformation: The amount of elastic deformation allowed by the geotextile will govern the deformation of the embankment. The maximum strain at the required stress is assumed to be approximately 10 per cent. This enables us to find the required modulus and failure strain in major principal stress direction and in minor principal stress direction for the geotextile.

60 E = T reqd /ε f E = modulus of elasticity T reqd = tension in the geotextile ε f = strain in the geotextile Pull out and anchorage: With the mobilization of all, or part of the fabric reinforcement s strength, the essential requirement is that the soil behind the slip zone resists pullout. Sufficient anchorage distance behind slip plane should be available to mobilize the required strength. L reqd. = T act / 2(C a + σ v tan ) where T act = Actual stress in geosynthetic C a = Adhesion of soil geosynthetic tan = Friction coefficient of the soil to geosynthetic L reqd = Required anchorage length behind the slip plane Lateral spreading: It is necessary to arrive at the frictional properties of geosynthetic by considering the tension cracks developed in the embankment and active earth pressure exerted on the side. Assuming the fill material above the geosynthetic to be granular, the following criteria must be satisfied. Tan = HK a /L where L = length of the zone involved in spreading Properties of materials The topsoil up to a depth of 2 m from the ground level is mainly silty sand and clay mixture. The soil below this depth is highly plastic clay. This soil in general found to have a natural moisture content ranging from 70 per cent to 85 per cent with bulk density varying from 1.3 g/cc to 1.45 g/cc. Undrained shear strength of the soil as determined from vane shear tests was found to be 4.6 kn/sq.m to 6.0 kn/sq.m. Compression index (C c ) varied from 0.15 to 0.29 and coefficient of consolidation (C v ) ranges between 1.l X 10-3 to 3.0 X10-3. Construction procedure The geotextile was available in width of 75 cm., so, 10 pieces of geotextile were stitched at the site to make the width to 7 m and 26 m long geotextile (base width of embankment is 23 m and anchorage length at both ends is 3 m) and were carried to the site. Before spreading the geotextile the site was cleared off all debris and any tree roots. Any rough surfaces which could not be cleared, were covered with sand to eliminate the damage to geotextile. The geotextile was laid with its warp direction (strong direction) parallel to the width of the embankment. A trench of size 0.5 m X 0.5 m X 0.5 m was dug in the soil on either side along the embankment length, for anchoring the geotextile. The geotextile was then placed in the trench and sand filling was done for proper anchorage. Ten pieces of geotextiles were stitched to bring the width to 7.0 m and length to 26.0 m. Base width of embankment was 23.0 m and anchorage length at both ends was 3.0 m. An overlap of 30 cm was given between two rolls of geotextiles. The geotextile was

61 stretched manually, so that no wrinkles were there while spreading, this would also build a small amount of initial tension in the geotextile. After spreading the geotextile and anchoring it at the two ends, a sand cushion of minimum 30 cm thick was laid, to take care of the damage due to moving trucks or any other vehicles. Soil filling in the embankment was continued in the usual manner. Settlement gauges were installed to monitor the settlement in the embankment. The jute geotextile was used for 110m length of the road stretch. Approximately a total of 3000 sq. m of jute was used in this project. Woven jute geotextiles with properties given in Table 26 was used at the experimental stretch at Kakinada Port area for reinforcement and also as a separator between the embankment and the soft subsoil. Monitoring of completed embankment i.e. both treated and control stretch, was carried out by JNTU College of Engineering, Kakinada. Table 26: Properties of Woven Jute geotextiles used at Kakinada Port Results and Discussion S. No. Property Test value 1. Thickness 5 mm 2. Weight 750 gsm 3. Tensile strength 15 kn/m 4. Elongation 10 per cent 5. Puncture resistance 350 N 6. Overlap length 300 mm 7. Type of fabric Woven At the end of seven months, the increase in shear strength of sub-soil ensured the required factor of safety for the embankment. The strength of fabric was no longer required to provide reinforcing effect. Brief details of some of the tests on sub-soil are given in Tables 27 to 29. Table 27: Water content of Soil before and after Laying of JGT Location Water content (%) before laying JGT Water content (%) after laying JGT at elapsed months of Table 28: Dry Density of Soil before and after Laying of JGT Location Dry Density (gm/cc) Dry Density (gm/cc) after laying JGT at elapsed months of before laying JGT

62 Table 29: Void Ratio and Compression Index of Soil at Different Elapsed Time Location Void Ratio Compression Index Before Laying Following Laying at Elapsed Months of Before Laying Following Laying at Elapsed Months of Conclusions Water content, void ratio and compression index decreased while insitu density increased by the use of jute geotextiles. Jute geotextiles appears to be very effective even in weak subgrade soils in reducing their compressibility and increasing their strengths as reflected from good performance even after a lapse of seven years PMGSY Pilot Project Using Jute Geotextile Jute Manufactures Development Council (JMDC), a national promotional body under Ministry of Textiles, Government of India, has embarked upon a Pilot Project under PMGSY with the support of Ministry of Rural Development/ National Rural Roads Development Agency. Central Road Research Institute (CRRI) has been appointed as Technical Consultant by JMDC. This project has been taken up in five states (Assam, Chattisgarh, Madhya Pradesh, Orissa and West Bengal). Ten roads, two in each state will have JGT as integral component of the road structure to study its usage as separator, filter, drainage medium and reinforcing material. The main objectives of this Pilot Project is to evaluate the beneficial effects of the use of JGT and standardise different types of JGT for different applications in road construction. The following aspects will be considered in the Pilot Project: 1. Benefit of woven/ non woven JGT as a separation layer, segregating and preventing interpenetration of material overlying and underlying the fabric 2. Benefit of non woven JGT as a drainage layer, facilitating in plane discharge of water that percolates through the upper layer of the pavement 3. Benefit of woven JGT as an initial basal supporting system for embankments on soft ground (slushy soil, marshy area, etc) 4. Benefit of open weave JGT as a bioengineering protective measure by facilitating growth of vegetation on the embankment slopes and earthen shoulders 5. Benefit of woven JGT as an agent of improvement in the load bearing capacity of subgrade The total length of ten selected roads is km and total estimated cost of construction is Rs Crores. Brief details of the ten selected roads are given in Table 29.

63 Table 29 Details of Ten Selected Roads for Pilot Project Using JGT State Name of the Road Road Length (km) Orissa Jadupur to Mahanangal, Kendrapara District 5.50 Orissa MDR 14 to Chatumary, Jajpur District 4.00 Madhya Pradesh Berasia to Semrakalan Approach Road, Bhopal 5.10 District Madhya Pradesh Gehlawan village to PMGSY road, Raisen District 3.14 Chattisgarh Kodavabani to Khursi Road, Bilaspur District 4.80 Chattisgarh Kherajiti to Ghirghosa road, Kawardha District 5.50 West Bengal Notuk to Dingal Road, West Midnapore District 4.80 West Bengal Nandanpur to Marokhana High School Road, 6.20 Hooghly District Assam Rampur Satra to Dumdumia, Nagaon District 4.20 Assam UT Road to Jorabari, Darang District 4.60 Total Length Detailed Project Report (DPR) for each of these roads was prepared by CRRI. The project roads are being constructed by respective state agencies through established tendering process being followed in case of any other PMGSY road. CRRI has been entrusted the job of quality management and third party random quality checking. Types of JGT in Use in the Project Different types of JGT which were developed by IJIRA have been chosen on the basis of soil survey carried out by CRRI in these project roads and the specific end use of JGT. Woven JGT to be used for separation function shall be having three different values of tensile strength 15 kn/m, 20 kn/m and 30 kn/m. Of all the three varieties of woven JGT, about 50 per cent of the material to be laid would be treated with a branded rot resistant textile friendly chemical (COMPSOL A blend of Copper Ammonium Carbonate solution and Ammonium Hydroxide conforming to specifications of WHMIS Workplace Hazardous Materials Identification Standards of USA and Canada). The remaining 50 per cent will be laid as untreated. This will enable carrying out a comparative study on the necessity of rot resistant treatment of JGT as a separator, filter and drainage medium above subgrade soil. Non woven JGT of 500 gsm has been used for facilitating drainage. Non woven JGT possesses low tensile strength but is an efficient drainage medium. In fact transmissivity criterion is more dominant than permittivity for geotextiles for efficient water dispersion from soil. Open weave JGT of 500 gsm will be used on the side slopes of road embankments and in shoulder areas of selected stretches for surfacial soil erosion control. This is a bio-engineering measure intended to improve slope stability and embankment integrity. Laying of open weave JGT would be followed by sowing the seeds of grass/ leguminous plants which will have deep roots and thrive under the local climatic conditions. In areas prone to water logging, woven JGT of 20 kn/m tensile strength will be treated with bitumen to prevent its early degradation due to prolonged contact of the fabric with water. Bitumen to be used for coating woven JGT shall conform to IS 702 (Industrial grade bitumen of grade 90/15). Bitumen absorption by the untreated JGT shall not be less than 60 per cent of its

64 weight. Work could not be taken up in two of the above roads due to frequent floods and other local problems. Construction work has been completed in six roads. Performance monitoring is in progress in five of these completed roads Jute Geotextile for Drainage and Filtration Function Design and Construction of Filter using Jute Geotextile Behind Retaining Wall, New Delhi The drainage filter should adequately satisfy its performance during and after construction of the structures. In case of high embankments constructed using fly ash (pond ash) as fill material, the drainage aspects of the fill material is of critical importance during construction period because of high permeability or fly ash. In the case of Road Over Bridge, such as Hanuman Setu, the filter criteria was critical during the construction, as the water percolation into the back fill was more during construction particularly in monsoon season. After construction of ROB, the percolation of water was negligible as the road pavement material was almost impermeable and camber of 1 in 30 also facilitates a faster run-off. Thus, the filter thickness requirement was more during construction than after construction. To facilitate quick drainage, jute geotextile was chosen as filter it can be effectively and economically used. A non woven jute geotextile would satisfy the filter criteria. Design criteria Fly ash was used as a backfill material in the said project. Because of lower specific gravity and finer gradation of the material, design requirement was more critical than the conventional backfill material. 750 gsm non woven jute geotextile was substituted for 30 cm thick conventional filter. Conventional filter was designed based on normal practice of IRC. The filter was designed according to the following criteria: D 15 of filter material < 4 to 5 D 85 of base material D 15 of filter material = 5 to 20 D 15 of base material D 15 of filter material = 2 to 4 Maximum opening size of pipe Grain size curve of filter material may be parallel to the base material. Gradation characteristics of different materials in this project are given below: i. Pond Ash D 15 = mm D 85 = 0.09 mm ii. Gradation type 1 (medium to course sand) D 15 = 0.45 mm D 85 = 3.0 mm iii. Gradation type 2 ( fine gravel, uniformly graded) D 15 = 15 mm = 20 mm D 85

65 Construction Fly ash was compacted in layers of 20 cm thickness up to the edge of the facing panel. Once the height reached up to the next geogrid level, trench of width 0.6m was excavated in the compacted fly ash. Jute geotextile was cut to the required size and placed vertically in the trench. Sand and coarse aggregates were filled in the trench and compacted. At the time when the construction of the embankment was just completed and only paving was left, about 100mm of rainfall occurred. From the visual inspection after the rainfall, it was found that jute geotextile retained the fine fly ash effectively and water drained through the jute geotextile JGT for Trench Drains at Joshimath Malari Road The stretch of Joshimath Malari Road at km 3.5 in Uttrakhand, had been experiencing subsidence and sinking for the last many years. The stretch is located on debris slide area and debris consists of micacious sandy silt. A number of seepage points were observed on the uphill as well as downhill slopes. The road was experiencing subsidence during the monsoon every year, inducing damages to the restraining structures. Breast walls constructed earlier had got damaged due to slip. During rainy season, the whole slope mass gets saturated and surfacial and sub-surfacial water flows down the slope. The subsurface water was flowing downhill side saturating the subgrade completely. The pavement thus experiences continuous gradual subsidence under repeated loading at many locations in the stretch. As a measure to arrest the sinking of road pavement, a systematic network of roadside trench drains and cross trench drains was proposed using non woven jute geotextiles (Fig 17 to 20). Conventional roadside trench drains consists of a shallow trench filled with graded aggregate filter material with or without a perforated pipe. Such a drain is difficult to construct as the procuring and placing of graded filter pose problems. Such drains even if constructed would lose its efficiency due to clogging as the fine materials enter the filter material and fill the voids. The trench drains were made of rubbles encapsulated in non woven jute geotextiles to prevent the finer particle entering into the voids of rubbles, thereby clogging the trench drains. About 1000 sq.m. of non woven jute fabric having 750 gsm has been used for drainage application on about 100 m. length of road stretch on Joshimath-Malari road during June, The monitoring of field experiments on this particular stretch of treated road was carried out in June, 1997 and has shown very encouraging and satisfactory results. There has been no further sinking and subsidence of the road at this location.

66 Fig 17: Plan View and Cross Section sub-surface drain Constructed Using JGT at Joshimath Malari Road Fig 18: Construction of Road Side and Cross Trench Drains Using JGT at Joshimath Malari Road

67 Fig 19: Construction of Road Side Trench Drain Using JGT Fig 20: Satisfactory Performance of the Road after one year

68 14.4 Jute Geotextile for Erosion Control of Hill Slopes On the basis of field studies, CRRI has come to the conclusion that at number of locations, shallow surfacial slides constitute a significant proportion of landslides in areas with moderate rainfall intensity and where soil cover is medium cohesive in nature. Most surfacial landslides occur as a result of denudation of vegetation on soil slopes consequent upon a cut being made for road construction purposes. Surfacial slides extend to only a couple of meters below the slope surface and originate as a result of erosion from flowing water. If erosion is allowed to proceed unchecked, there is the possibility that the damage may spread laterally or the depth of erosion may increase, eventually resulting in a much larger damaged slope area. Vegetative turfing represents one of the most important corrective measures in either case. In the case of freshly exposed cutting made for road construction, vegetative turfing is important, even as a preventive measure. In the case of deep-seated slides, however, vegetative turfing is only one of the ingredients of the total mix of corrective measures and as such it can prove to be effective only when conjointly implemented with other corrective measures. Vegetative turfing has proved to be, by and large, the most economical and simple means of protecting slopes of hills and embankments against erosion. Based on several field trials carried out by the Institute, technique has been developed for treatment of erodible slopes as a part of landslide correction works either singly or in combination with other techniques. Brief details of the technique are given below; The barren slopes are initially demarcated, graded and fertilized. The levelling of the area must be ensured so that when netting is laid it would cover the entire area flush to the ground resulting in run-off water flowing over the netting/geogrids. First a dose of seed broad casting of locally available perennial grasses is done. Thereafter, jute netting/geogrid of 1.25 cm to 2.50 cm openings size and having roll width of 1.0 m to 1.25 m, is laid on the prepared slope surface firmly in the direction of water-flow. The widths of netting are secured against displacement by an overlapping of 5 cm to 8 cm and stitched or pegged down with 15 cm long steel nails about 1.0 m apart. The top and bottom ends of the fully stretched jute netting are fixed/ anchored in trenches of 30 cm depth. Afterwards, another dose of seed broadcasting and dibbling of locally available grasses 15 to 20 cm apart, row to row is carried out. The jute net provides innumerable miniature check dams thus absorbing the impact and kinetic energy of the falling rain drops and surface runoff, thereby, reducing its erosion potential. The soil, seed, grass root slips are kept in situ without being dislodged, thereby, getting full benefit of moisture. After the first rainy season, the seeded and sprigged vegetation soon envelops the entire surface thus protecting the slopes permanently. Jute geogrid have been observed to have a life of about 2 to 3 years in the field, which is sufficient in fully promoting the growth of vegetative cover over the denuded slope. Once vegetative growth is established within two monsoon seasons, the mission is accomplished for the jute geogrid. At the end of jute geogrid s life, the geogrid decomposes and in the process adds nutrients to the soil. The method proved

69 particularly successful if it is so timed that advantage is taken of the increased moisture content of the soil resulting from the first couple of monsoon showers Hill Slopes on Kaliasaur Landslide A study was taken up by CRRI to assess the causes of landslide both on Kaliasur. A number of causative factors were determined to analyze the slopes on to suggest the remedial measures. Kaliasaur landslide is very old which is operative since Since then it has repeated itself a number of times. Records show that this landslide reactivates almost every few years. The landslide is situated at the bank of meandering Alaknanda at km.147 on Haridwar-Badrinath road. Disastrous occurrence of the landslide event happened in September 1989 when it blocked about one fourth of the river Alaknanda, which flows about 100 m below the road level. Geology of Slide Area The main rock types in the slided area are represented by pink quartzite, maroon slates, dolomitic limestone and metabasic. The rock in the area is faulted and jointed. These rocks are show effect of cataclasis and mylonitisation. The rocks are marked by a number of mesoscopic shears. The rock in the upper portion of the slide was found to be in weak state, weathered and fractured. Quartzite has developed bedding joints, opening out on the free face towards the road, where as the slate bands are highly fractured. There are a number of scree zones. Scree deposits and fractured quartzite occupy the lower part of the slide. The length of the road affected by the slide area is approximately 300 m. The slope angle ranged from 40 degree to 50 degree. The height of the crown above the road level about 165 m. The slide was multitier slide having combination of surfacial and deep seated movements. The area around the slide is thickly forested. Mechanism of Slide The crown portion of the slide appeared nearly vertical with a height of about 15 m concaving towards the road and was in unstable condition. Village Chatikhal is situated less than a kilometer away from the crown of the slide. A series of tension cracks existed in the area between the crown and the village. The slided portion was found in denuded state both uphill side as well as down hillside of the road. The concave portion of the crown had become a shelter house for wild animals like deers and wild goats. The rock pieces break under the impact of the foot of the running animals and start falling down the steep slope. The upper portion of the slope was quite steep, of the order of 60 0 to And the falling pieces attain high speed. A falling stone hits another stone resting on the slope, which also starts falling down. In this way, a chain reaction was created setting into motion a number of stones and movement of the loose debris material. This sustained movement of the debris prevented vegetation growth and thus the slided portion remained in denuded condition for the last about 50 years. Installation of Jute Geogextile It was proposed to install jute geogrid on the denuded debris mass. The main object of the installation of jute geogrid at this site was to stop the sustained movement of the slope debris and need for plantation to be carried out. The uphill site slope material consists of gravel with fine

70 soil, existing in a heterogeneous state. One thousand square meter of jute geogrid was used to protect an area on the denuded slope. The jute geogrid was in the form of rolls of width 1.2 m and of continuous length. The total area or the slide debris is approximately 5000 sq.m. So, with 1000 sq.m. only a part or the slope area could be covered. Top length of about 60 m of the slide consists of partially weathered rock. The area covering a length of about 50 m below this was selected for installation of jute geogrid. Geogrid pieces of 60m length were cut and a layer was laid. The top and lower ends of the geogrid were buried into trenches of about 50 cm. depth. Next length was similarly placed alongside of first length and the two lengths were stitched together. In this way, the entire fabric was laid to cover 1000sq.m. of the area. Steel nails of about 6 mm diameter and of 40 to 50 cm in length were also used to anchor JGT at various selected locations in the entire covered area. The fabric was laid in the month of June The executing authority was requested to identify locally available bushes and shrubs and carry out the plantation work during the coming monsoon. It was also advised to periodically spread the seeds of these plants. Some photographs showing the laying of geotextile is shown in Fig 21. In this manner by promoting the vegetation growth, the landslide activity at Kaliasaur has been contained to a large extent. Fig 21: Stabilisation of Hill Slope Kaliasaur Landslide

71 Field Experiments for Erosion Control in Himachal Pradesh A denuded slide area was selected in Himachal Pradesh in April 1997, where only jute geogrid was needed to be used for erosion control. The slide area is located at km at Sataun near Poanta Sahib on SH -1 in H.P (Fig 22 and 23). The width of the slide area is about 30 m and the height of the crown of the slide above the road level is about 120 m. In order to prevent the movement of debris and promote the growth of vegetation on slopes, which are in the denuded condition, about two thousand square metres of jute, geogrid was installed in June,1997. The specifications of jute geogrid are given in Table 27. Locally available plants and grasses were dibbled subsequent to the installation of jute geogrid over the slope. The treated experimental stretch was monitored for its performances for a couple of years. Monitoring showed very good performance of JGT in promoting vegetation growth and containing surfacial slides. Table 27: Specifications of Jute Geotextile installed at Sataun (H.P) Description Material Type Grid size Mass Form Properties 100 per cent Jute Open Weave with square grids 2.5 cm x 2.5 cm 750 gsm Continuous rolls of 1.2m width Fig 22: Laying of Jute Geotextile at Sataun

72 Fig 23:Slope at Sataun Covered with vegetation after JGT Application Rehabilitation of Mine spoils at Sahasradhara The CSWCRTI, Dehradun selected a highly degraded abandoned limestone mined watershed near Sahasradhara in Doon valley in the outer Himalayas for rehabilitation by integrated soil and water conservation measures on watershed basis. Geo-jute was used to rehabilitate the highly erodible mine spoil slopes as described below. Description of the watershed Sahastradhara Limestone quarry watershed area measuring 64 hectares, is situated in the lesser Himalayan zone of Doon valley at an altitude from 820 m 1310 m above msi. Surface mining operations results in a huge quantity of over burden. The over burden to mineral ratio being as high as 5:1. Mineral rejects and overburden piled up at several places in the watershed were highly erodable and difficult to vegetate due to absence of top soil and poor fertility. The area receives an annual rainfall of about 3000 mm, 80 per cent of which is received during monsoon months (June to September). The area is characterised by Krol belt comprising limestone, gypsum, marble, slates and dolomite, etc. The mine spoil is sandy loam in texture with high gravel content. (60 per cent of the material is greater than 16 mm size), alkaline (ph 8.0), calcareous (CaCO³ 61 per cent) and poor in fertility status (Organic carbon 0.13 per cent, Nitrogen 0.02 per cent and available P 2 O kg per hectare) and poor water holding capacity (Dadhwal et al. 1992). The poor fertility of the mine spoil inhibits the growth of vegetation. The watershed is having an average slope of 50 per cent, at some points the slopes are exceeding even over 100 per cent.

73 The unscientific mining operations destroyed almost all the vegetation cover of the area comprising of mixed deciduous forest species of subtropical type. This along with high rainfall and steep slopes caused heavy debris movement from the watershed, leading to frequent vehicular disruption, entailing a huge recurring maintenance cost annually. The siltation of the river downstream led to frequent floods in monsoon destroying agricultural and other forest lands. Geo-jute for mine spoil rehabilitation Geo-jute was tried to give temporary protection to these slopes and help protect the vegetation till it establishes. The specifications of the geo-jute used were: Weight 500 g/m 2, strand thickness 5 mm and open area 65 per cent. Different slopes (30 70 per cent) covering an area of 0.86 hectare were treated. Besides geo-jute, synthetic geo-textiles were also experimented for their performance. Application technique Seeds of suitable tree species (Acacia catechu, Leucaenaleucocephala etc.), were spread on the area and scarified. Grass mulch locally available was spread at the rate of 2 3 ton per hectare. Geo-jute was spread on the area loosely. The two adjoining widths were overlapped by about 10 cm and fastened with jute threads. Wooden sticks were driven to hold the mesh at place. Rooted slips of grasses like Saccharum spontaneum (Kans) and Thysanolaena mixima (broom grass) and cuttings/root slips/rhizomes of ipomoea carnea, cites negundo, Arundo donax and hybrid napier were planted in openings between strands at close spacings. The technique for application of geo-jute is shown in Fig.3. Vegetation Growth In the geo-jute area there was good growth of grasses compared to control section. Thysanolaena maxima grass recorded an yield of 3052 kg per hectare (oven dry) compared to 640 kg per hectare in control after 3 years of plantation. Hybrid napier when planted in contour trenches filled with good soil mixed with farm yard manure (FYM) recorded an excellent yield of 9850 kg per hectare compared to 1960 kg per hectare in control, Saccharum spontaneum also showed good performance. The grass roots provided good anchorage to the soil in the second year of plantation itself. Survival of tree species was observed to be poor. The geo-jute biodegraded in about two years, by then the vegetation cover had established itself. The vegetation cover in the geo-jute applied area was better than the vegetation cover in the synthetic geo-textiles applied area. Moisture improvement The geo-jute helped in moisture conservation by upto 50 per cent. It was observed that in the geo-jute area the moisture content reached below wilting point in 7 days compared to 3 days only in control after a rainfall of 20 mm (in the top 15 cm layer). In seven days period, the seeds can germinate and moisture in deeper layers can sustain the tender plants. There was still good amount of moisture below 30 cm depth after one month from the day of occurrence of 20 mm rainfall event.

74 Slope Protection of Eastern Approach Embankment of Ishwar Gupta Setu over Hooghly River at Kalyani, West Bengal Eastern Approach Embankment of the bridge 8 m high without any sub-bank was eroded due to heavy rains during consecutive monsoons, the stability of the slope of the high embankment was at stake. A programme for application of Jute Geotextiles on the slope was chalked out in collaboration with Jute Research Laboratory in Open mesh JGT was applied on the slope after mending the damages and depression on the slope. The JGT mesh was anchored with iron hooks at suitable interval. Seeds of suitable grass were spread on mesh. The grass had grown rapidly resulting in dense grass carpet on the slopes of the embankment. This prevented any further erosion of soil from the slopes of the embankment, which was kept under constant observation. Even after a lapse of a decade no additional provisions like construction of sub-bank was needed for protection of the embankment Jute Geotextile to Prevent Reflection Cracks The Jute Geotextile was tried in a portion of a busy road (Garia Station Road) at the outskirts of Kolkata in February 2002 in association with 24 Paraganas Highways Division under Public Works (Roads) Department, Government of West Bengal. This road takes off from Raja S C Mullik Road near Garia junction in the southern fringe of Kolkata passes through a fast developing urban cluster and is subject to heavy traffic. Consequently this road had suffered extensive distress in the form of cracks and potholes. The State PWD was resorting to routine upkeep measures. The road had poor lateral drainage in a particular stretch of 1 km and under review due to encroaching structures on its either side. Even modest showers resulted in water stagnation on the road which, under the effect of vehicular loading resulted in loosening of aggregates in the wearing course leading to formation of potholes. When JGT application was taken up, about 500 metres of the road length was heavily distressed. The wearing course was virtually non-existent. Signs of subgrade settlement were also evident. The affected stretch was initially levelled with aggregates and rolled. The prepared surface was applied with a bitumen tack coat at the rate of 3 kg/10m 2. Jute Geotextile as per the specifications given in Table 33, was laid and lightly rolled (Fig 24). Another coat of bitumen was applied over JGT at the rate of 5 kg/10m 2 followed by a layer of pre-mix carpet and seal coat. Thickness of the overlay was kept as 20 mm. The width of paved area treated was 7 m. Table 33 Properties of JGT Used as Crack Arresting Layer Geotextile Characteristics Typical Properties Type of Geotextile Open mesh woven jute geotextile Weight (g/m 2 ) 292 Threads/dm (MD x CD) 12 x 12 Thickness (mm) 3 Width (cm) 122 Open area (per cent) 60 Strength (kn/m) (MD x CD) 10 x 10

75 Cracks on Garia Station Road JGT laid in wearing Course followed by Premix carpeting Finished Road with JGT on wearing course Condition of the road after three years of treatment with JGT Fig 24: Laying of Jute Geotextile in prevention of reflection cracks

76 The treated stretch was inspected in December, 2002 after it was subjected to one full monsoon season. Table 34 will reveal the conditions prevailing before and after the treatment. Table 34 Condition Survey of the Road Condition before laying JGT Potholes Cracks Pothole area / No. per cent Area per cent Depth m per cent (Average Depth 75mm) Condition after laying JGT m Nil Evidently the road was found to be in a better shape after the treatment compared to the adjoining stretches where JGT was not applied with the overlay. The trial brought out the fact that JGT may help in reinforcing the bituminous overlay. List of some important field trials using jute geotextile are given in Appendix III, available standards at Appendix IV and list of manufacturers are given in Appendix V. 15. International Usage of Jute Geotextiles Though there has been persistent demand of Jute Geotextiles in the overseas market especially in the USA, Australia and several European countries. JGT has been used for erosion control related applications in these countries since many decades. In the early 1940s, the British established a Jute Mill in Calcutta (The Ludlow Jute Mills), one unit of which was only producing jute mesh (now known as soil saver). Since the beginning it was an export item, probably to U.K. and now there are a quite a few mills in Calcutta which continue to produce this product and supply overseas. In recent times, jute is being used for erosion control in the United States, where soil conservationists have taken a modified form of the jute mesh used to warp bales of cotton and laid it on slopes to prevent wash-off from newly seeded ground. Even earlier, jute fabrics were reportedly used in the construction of Kingsway Road in Dundee, Scotland for erosion control in cutting slopes (ITC, 1991) on the same road. Few erosion control materials have been around as long as jute. Perhaps the best reason to use jute mesh is that its performance has been proven for nearly 3 decades, not only in the U.S. but in Europe, Asia and Canada as well. The table 35 below shows the quantum of Jute Geotextiles (open weave and non woven variety) exported from India since The figures, however, do not include Woven Jute Geotextiles which are included in the category of hessian, the largest exportable jute product.

77 Table 35 Quantity of Jute Geotextiles exported from India Year Soil Saver (Open Non-woven JGT Weave JGT) 000 MT 000 MT Source-DGCI & S, Kolkata There are references aplenty on the studies conducted in the foreign universities on Jute Geotextiles. The pioneering research on road application of Jute Geotextiles was done by Prof. S. D. Ramaswamy and Prof. M. A. Aziz of National University of Singapore in Outdoor field tests conducted in Parker, Colorado by Fifield and Malnor (1989) assessed the erosion control effectiveness of 32 different products, including blankets, hydromulches, tackifiers and geotextiles. Data was collected for three years, Numerous parameters of erosion were evaluated including the C Factor, sediment production (soil loss), runoff (water leaving plots and vegetative production. The C Factor for the 32 products ranged from Jute showed a C Factor of (the smaller the number, the better the performance) for a 3:1 slope and for a 1:5:1 slope. This means that jute retained 99.6% (3:1 slope) and 99.5% (1.5:1 slope) of the sediment expected to be lost from bare ground. From these tests, it is apparent that jute is one of today s top performing erosion control products. Extensive research has also been carried out in Cranfield University, UK (Silsoe College) by Prof. Jane Rickson on open weave Jute Geotextiles used for erosion control in road embankments. A significant study on Jute Geotextiles was made by Dr. T. S. Ingold and Mr J Thomson who, as consultants to the International Trade Centre, UNCTAD/GATT, Geneva, submitted several reports on applications and marketability of Jute Geotextiles in European countries to the Common Fund for Commodities and the International Jute Organization (now International Jute Study Group). Brief details of some of the specific international case studies of JGT usage are given below:

78 15.1 Erosion Control Using JGT at Vail Pass, Colorado, USA During the mid 1970 s, a 22 km stretch of Interstate No 70 in Colorado, USA was constructed over mountainous terrain in central Colorado. This project, known as Vail Pass, involved one of the most intensively researched and planned Interstate Projects to-date, utilising a cooperative effort of Federal/State Highway and USDA forest service administrators, Colorado Division of Wildlife personnel, private consultants and other state and local agencies. Crossing the continental divide at an elevation of 10,500 feet the project had to address numerous environmental factors relating to erosion control, wildlife habitat, revegetation and preservation of a fragile and scenic alpine landscape. Jute mesh was selected as the primary erosion control material for all slopes steeper than 3:1. More than 200 acres were covered with jute, demonstrating the confidence which the project designers had in the ability of jute to perform as needed for this environmentally sensitive project. Placed over straw or hay mulch, the jute effectively stopped rill and gully erosion common on highway slopes at this altitude. To create a more natural appearance, slope preparation included the placement of large boulders, tree stumps and shrub/tree plantings. The jute proved easy to place over and around these landscape components and could also be planted through, where smaller woody material was used. Project evaluations of the treatments used to control water quality and erosion were conducted by the USDA Forest service. Their evaluations stated that the use of jute over hay/straw mulch proved to be highly successful, providing immediate erosion control protection during establishment of vegetation cover. the slopes of Vail Pass were protected from erosion and revegetated, quickly transforming a difficult construction project into an aesthetically pleasing and ecologically functional landscape JGT Use for Road Project in Meridian, Mississippi, USA This case study, completed in 1987, incorporated the use of jute and soil bioengineering techniques. The site is a logging road cut slope located on the boundary of the meridian Naval Air Station in central Mississippi. The section of cut slope treated was approximately 3 m high by 22 m long, very steep (1.25:1) and it had been severely eroded. The top bank had been steadily undercut, gullying and shallow mass wasting were well defined and almost no vegetation existed on the slope. Most of the erosion had been caused by rainfall, with ground water seepage also contributing to the slope deterioration. The project design included the use of a soil bioengineering system called live fascines (live branches tied together in sausage-like bundles) combined with jute mesh. The jute served two important functions. It was used to line trenches within which the fascines were placed and was applied over the critical crown and foot sections of the slope. The site was evaluated twice in 1987, once at 12 weeks and again at 20 weeks after installation, which took place in February, Both inspections found the soil stability of the cut bank had greatly increased overall and where shallow mass wasting was occurring before installation, no further loss of soil had occurred. No gullies or rills had developed where the jute mesh fabrics

79 systems were in place. In less than six months the slope had been stabilised and was supporting vigorous plant growth. Erosion had been effectively controlled. Jute ensured success of this difficult site Erosion Control using JGT in Mine Areas, Southeastern Ohio, USA This case study refers to usage of JGT for erosion control in coal mine areas. A coal mine in Muskingum County of southeastern Ohio has been using jute to revegetate ditches and swales. Use of jute has helped the mine agencies to meet stringent reclamation regulations for erosion control. The mine uses jute mesh primarily for revegetation of drainage channels where slopes of 12 per cent to 18 per cent occur. These areas are seeded, mulched with hay or straw then covered with jute. Over the years, performance of jute has been consistent, stabilising soil and promoting a vegetative cover within as little as 6 weeks. Jute has allowed the environmental team at the mine to use less rip-rap for the gentler ditches and swales, helping the mine to save money. For a given budget, JGT can control erosion over a larger area than more expensive erosion control products. Applications of 5,000 10,000 sq. m of jute per year are common in this project. Ease of installation and erosion control protection for up to two growing seasons are additional seasons why jute is used year after year. With 15 years of performance at this site it was obvious that jute meets this mine s erosion control needs Application of JGT on Rural Roads of Bangladesh for Slope Protection JGT was successfully used for slope protection work on Pakulla-Lauhati Road of Delduar Upazilla, under District Tangail about 80 km north of Dhaka, Bangladesh. In this study, treated JGT was used. JGT resembling PVD (Band Drains) were installed in the embankment area adjoining a river. Sandy soil was used for construction of embankment and JGT was used to provide cover to this embankment slope and also to promote vegetation growth on this slope. In a similar manner, successful application of JGT for erosion control and prevention of landslides have been reported from hilly areas of Chittagong in Bangladesh Use of JGT in road projects in UK Rickson (2000) has reported several case studies in UK wherein JGT has been used successfully. Rickson has reported that due to better water holding capacity, geotextile induced roughness to the flow of run-off water, ponding of flow by geotextile, etc, JGT performed better than other types of geotextiles when used in erosion control applications. Geotextiles can be used to enhance soil s bearing capacity. She has reported that by tensile strength of JGT is on the lower side compared to present day specifications, which have been obviously evolved keeping in view polymeric geotextiles. Some photographs collected from various sources on application of Jute Geotextiles in foreign countries are also appended herewith (Fig 25 to 27).

80 Slope stabilization of slope of road embankment with JGT Slope stabilization of slope of road embankment with JGT Stabilized slope of railway embankment with JGT Fig 25 APPLICATIONS OF JGT IN EUROPE

81 Sprouting of vegetation through JGT Laying of JGT on slope of road embankment Installation of JGT on the prepared road sub-grade Fig 26 APPLICATIONS OF JGT IN EUROPE

82 Laying of JGT (RECP) on slope of road embankment Installation of JGT for slope stabilization Fig 27 APPLICATIONS OF JGT IN AUSTRALIA

83 APPENDIX I JGT Manufacturing Process Photographs Softening Piling Softener Emulsion Application Carding

84 SPINNING DRAWING

85 WINDING BEAMING

86 WEAVING

87 PACKING (Typical Jute Bale)

88 NON - WOVEN JGT FABRIC 500 gsm 1000 gsm

89 APPENDIX II EQUIPMENTS AVAILABLE IN INDIA FOR TESTING JUTE GEOTEXTILES THICKNESS GAUGE TESTER WITH JGT SAMPLE

90 UNIVERSAL TENSILE TESTING MACHINE (U.T.M) PUNCTURE RESISTANCE APPARATUS

91 CALIFORNIA BEARING RATIO TEST APPARATUS DIRECT SHEAR TEST APPARATUS

92 CONE DROP TESTING EQUIPMENT AFTER TESTING WITH JGT SAMPLE APPEARENT OPENING SIZE TESTING MACHINE WHEN READY WITH JGT SAMPLE

93 SIEVE BRASS FRAME OF DIFFERENT SIZES WET SEIVE TEST APPARATUS with JGT Sample

94 FLOW RATE,PERMEABILITY & PERMITTIVITY TESTING APPARATUS WITH JGT SAMPLE

95 BTRA PERMITTIVITY TESTER IN-PLANE PERMEABILITY TEST APPARATUS

96 PERMEABILITY TESTING APPRATUS FOR SOIL GRADIENT RATIO TEST APPARATUS

97 LONG TERM FLOW TEST APPARATUS