SOIL STABILISATION FOR BLACK COTTON SOILS USING GEONAILS AND YARD WASTE

Transcription

1 SOIL STABILISATION FOR BLACK COTTON SOILS USING GEONAILS AND YARD WASTE R.Santhosh #, V.Dinesh * ABSTRACT - Black cotton soils are highly clayey soils grayish to blackish in color. They contain montmorillonite clay mineral which has high expansive characteristics. Black Cotton soils have low shrinkage limit and high optimum moisture content. It is highly sensitive to moisture changes. While laying roads or constructing foundations, the sub grade and its undesirable characteristics need to be modified using a suitable stabilization technique. Stabilization involves the methods used for modifying the properties of a soil to improve its engineering performance, mainly to increase the strength or stability of soil. Coimbatore is predominantly blessed with black cotton soil. The use of waste materials to stabilize the soil and make it as strong and stable as any other soil is the primary objective of the project. For this, we need to choose admixtures that may help in stabilization. The use of waste materials as admixtures would be the best suitable option. The use of yard waste and geonails in combination may prove to be an ideal solution for increasing the strength of the soil and that too in a rapid manner. Geonails are good stabilizing agents, but they are not effective on clays due to poor bonding and softness of clay. Therefore yard waste is used as a catalyst to make the soil hard enough for intrusion by geonails, which would then impart high strength in quick time. The paper discusses the theory behind combined use of yard waste and geo nails as soil stabilization agents and the experiences gained through an experimental study at an agricultural field in outskirts of Coimbatore. From the study, it can be concluded that the combination of geonails with yard waste help in stabilizing the black cotton soil KEYWORDS blackcotton soil, stabilization, geonails, yardwaste, Coimbatore, andipalayam, field study # R.Santhosh is Assistant Professor, Department of Civil Engineering, Kalaivani College of Technology, Coimbatore. * V.Dinesh is Assistant Professor, Department of Civil Engineering, Sri Ramakrishna Institute of Technology, Coimbatore. I. INTRODUCTION Black cotton soils occur mostly in 20% of the total area of India. Because of their high clay content, black soils develop wide cracks during the dry season, but their ironrich granular structure makes them resistant to wind and water erosion. They are also highly moisture-retentive, thus responding well to irrigation. They enrich agrofriendly contents make black cotton soil fertile. These soils are highly moisture retentive, thus responding well to irrigation. These are enriched with calcium carbonate, magnesium, potash and lime which are all nutrients. Poor phosphoric contents render rich production of corps like cotton. The iron-rich granular structure makes them resistant to wind and water. Fertility, erosion resistance, and properties of retaining moisture in their grain are the most useful condition for better crops growth. So these soils are the best option for farmers who like to produce plenty of crops. On the flip side, these soils contain fine clay particles. This property induces a great affinity to water of such type of soil. Alternate swelling and shrinkage in extensive limit during wet and dry process respectively results cracks in soil without any warning. So building to be founded on this soil may suffer severe damage with the change of atmospheric conditions. Highway and construction of structures on Black cotton soils has been a challenge to the respective engineers and designers because of its high swelling and shrinkage characteristics. This major group of soil consists of inorganic clays of medium to high compressibility. The Black cotton soil is very hard when dry, but loses its strength completely when in wet condition. The construction of any building on black cotton soil requires suitable stabilization measures. II. SOIL STABILISATION 16

2 Stabilization in a broad sense incorporates the various methods employed for modifying the properties of a soil to improve its engineering performance. Stabilization is being used for a variety of engineering works, the most common application being in the construction of road and airfield pavements, where the main objective is to increase the strength or stability of soil and to reduce the construction cost by making best use of locally available materials. It must also be recognized that stabilization not necessarily a magic wand by which every soil property is changed for the better. Correct usage demands a clear recognition of which soil properties must be upgraded, and this specific engineering requirement is an important element in the decision whether or not to stabilize. Properties of soil may be altered in many ways, among which are included chemical, thermal, mechanical and other means, The chief properties of a soil with which the construction engineer is concerned are: volume stability, strength, permeability, and durability. The methods of stabilization may be grouped under two main types (1) Modification or improvement of a soil property of the existing soil without any admixture and (2) Modification of the properties with the help of admixtures. Compaction and drainage are the examples of the first type, which improve the inherent shear strength of soil. The examples of the second type are: mechanical stabilization, stabilization with cement, lime, bitumen and chemicals etc. A new stabilization agent that has gained wide acclaim is soil nailing or geo nailing that has a wonderful impact on the soil properties. III. GEO NAILS Soil nailing is a construction technique that can be used as a remedial measure for expansive soils. This technique involves the insertion of relatively slender reinforcing elements into the slope often general purpose reinforcing bars (rebar) although proprietary solid or hollow-system bars are also available. Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line, whereas hollow bars may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses. Soil nail components may also be used to stabilize retaining walls or existing fill slopes (embankments); this is normally undertaken as a remedial measure or even for very weak soils. The soil nailing technique was developed in the early 1960s, partly from the techniques for rock bolting and multi-anchorage systems, and partly from reinforced fill technique. Normally 12 mm and 10 mm rebars are used for soil stabilization on poor soils for major constructions GEO NAIL INSTALLATION There are a variety of soil nail installation methods. The choice of installation method depends on a number of factors such as cost, site access, working space, and ground and groundwater conditions. A brief description of the commonly available soil nails installation methods are as follows. Drill-and-Grout: This is the most common installation method, both in Hong Kong and overseas. In this method, a soil-nail reinforcement is inserted into a pre-drilled hole, which is then cement-grouted under gravity or low pressure. Various drilling techniques, e.g., rotary, rotary percussive and down-the-hole hammer, are available to suit different ground conditions. The advantage of this method is that it can overcome underground obstructions, e.g., corestones, and the drilling spoil can provide information about the ground. In addition, long soil nails can be installed using the method. The size and alignment of the drillholes can be checked before the insertion of reinforcement, if needed. However, the drill-and-grout method may result in hole collapse. To overcome this problem, casing is required. The drilling and grouting process may also cause disturbance to the ground. Self-Drilling: This is a relatively new method when compared with the drill-and-grout method. The soil-nail reinforcement is directly drilled into the ground using a sacrificial drill bit. The reinforcement, which is hollow, serves as both the drill rod and the grout pipe. The installation process is rapid as the drilling and grouting are carried out simultaneously. Instead of using air or water, cement grout is used as the flushing medium, which has the benefit of maintaining hole stability. Centralisers and grout pipes are 17

3 not needed, and casing is usually not required. However, self-drilling soil nails may not be suitable for the ground containing corestones as they cannot penetrate through rock efficiently. It may be difficult to ensure the alignment of long soil nails due to the flexibility of reinforcement. Driven: Soil-nail reinforcement is directly driven into the ground by the ballistic method using a compressed air launcher, by the percussive method using hammering equipment, or by the vibratory method using a vibrator. During the driving process, the ground around the reinforcement will be displaced and compressed. The installation process is rapid and it causes minimal ground disruption. However, due to the limited power of the equipment, this method can only be used to install soil nails of relatively short length. Moreover, the soil-nail reinforcement may be damaged by the excessive buckling stress induced during the installation process, and hence it is not suitable for sites that contain stiff soil or corestones. As the soil-nail reinforcement is in direct contact with the ground, it is susceptible to corrosion unless noncorrodible reinforcement is used. 3.2 GEONAIL SYSTEM COMPONENTS A soil-nailed system formed by the any of the above methods comprises the following basic elements: (1) Soil-nail Reinforcement - A soil-nail reinforcement is the main element of a soil-nailed system. Its primary function is to provide tensile resistance. The reinforcement is typically a solid high yield deformed steel bar. Other types of materials, such as fibre reinforced polymer, can also be used as soil-nail reinforcement. (2) Reinforcement Connector (Coupler) - Couplers are used for joining sections of soil-nail reinforcing bars. (3) Cement Grout Sleeve - Cement grout, made of Portland cement and water, is placed in a pre-drilled hole after the insertion of a soil-nail reinforcement. (4) Corrosion Protection Measures. Different types of corrosion protection measures are required depending on the design life and soil aggressivity. Common types of corrosion protection measures are hot-dip galvanising and corrugated plastic sheathing. Heat-shrinkable sleeves made of polyethylene and anti-corrosion mastic sealant material are commonly used to protect couplers. (5) Soil-nail Head. A soil-nail head typically comprises a reinforced concrete pad, a steel bearing plate and nuts. Its primary function is to provide a reaction for individual soil nails to mobilise tensile force. surface and between soil nails. The diagrammatic representation of the system is as follows Fig. 1. Geo Nail System Illustration 3.3 GEONAIL MERITS AND DEMERITS The soil nailing technique offers an alternative design solution to the conventional techniques of cutting back and retaining wall construction. The following are typical merits of adopting the soil nailing technique in respect of construction, cost and performance: (a) It is suitable for cramped sites with difficult access because the construction plant required for soil nail installation is small and mobile. (b) It can easily cope with site constraints and variations in ground conditions encountered during construction, e.g., by adjusting the location and length of the soil nails to suit the site conditions. (c) During construction, it causes less environmental impact than cutting back and retaining wall construction as no major earthworks and tree felling are needed. 18

4 (d) There could be time and cost savings compared to conventional techniques of cutting back and retaining wall construction which usually involve substantial earthworks and temporary works. (e) It is less sensitive to undetected adverse geological features, and thus more robust and reliable than unsupported cuts. The soil nailing technique has the following main limitations: (a) The presence of utilities, underground structures or other buried obstructions poses restrictions to the length and layout of soil nails. (b) The zone occupied by soil nails is sterilised and the site poses constraints to future development. (c) Permission has to be obtained from the owners of the adjacent land for the installation of soil nails beyond the lot boundary. This places restrictions on the layout of soil nails. (d) The presence of high groundwater levels may lead to construction difficulties in hole drilling and grouting, and 20 instability problems of slope surface in the case of soil-nailed excavations IV. YARD WASTE Yard waste is a common term that is used to refer waste leaves that fell from trees and gardens. All yards produce waste from pruning, lawn mowing and other routine plant care activities. These wastes contain high organic content and composting is a way to reduce the volume of organic wastes and return them to the soil to benefit growing plants. Organic matter improves the drainage and aeration of clay soil. Compost is a soil amendment, not a fertilizer. It contains limited plant nutrients. Yard Waste can also be used a soil stabilizing agent or more importantly soil softening agent. Yard waste is normally applied in equal layers at regular intervals. The characteristics and composition of yard wastes may vary from place to place and therefore the quantity of yard waste has to be worked out on the basis of the type of leaves and the type of soil. V. COMBINED USE OF GEONAILS AND YARD WASTE FOR STABILISATION Coimbatore is predominantly blessed with black cotton soil. The black cotton soil resources are very useful in terms of agriculture, but the construction of any sort of structures on the soil is a challenge for civil engineers. For any construction activity, we need to choose admixtures that may help in soil stabilization. All the same, the use of waste materials as admixtures would be the best suitable option. In this context, the combined use of geonails and yard waste is proposed. Geonails are good stabilizing agents, but they are not effective on clays due to poor bonding and softness of clay. Therefore yard waste is used as a catalyst to make the soil hard enough for intrusion by geonails, which would then impart high strength in quick time. The use of yard waste and geonails in combination may prove to be an ideal solution for increasing the strength of the soil and that too in a rapid manner. VI. FIELD STUDY M/s Navrang Flyash Bricks is an industry involved in production of hollow and flyash bricks. They have a production unit at Idayarpalayam near Kavundamplayam and are proposing a new unit at Andipalayam village near Perur. The land at Andipalayam village is predominantly black cotton soil and for making a foundation for the machine and the unit, the company is interested in doing soil stabilization. In this regard, we had embarked on a project to study the soil stabilization for the black cotton soil in that area using a combination of geonails and yard wastes. We would perform a field study on few trial pits of the land and shall conduct a trial on the combined use of geonails and yard wastes and study the impact of the stabilization on the engineering properties of the soil. 6.1 PROJECT STEPS The project would logically involve the following steps (1) Creation of 4 Trial Pits (2) Study of Engineering Properties of Soil (3) Study on Pit 1 No Stabilization (4) Study on Pit 2 Stabilisation using Geonails (5) Study on Pit 3 Stabilization using Yardwaste 19

5 (6) Study on Pit 4 Stabilisation using Yard waste & Geonails (7) Comparison of Soil Stabilized Pits (8) Conclusion and Findings 6.2 CREATION OF TRIAL PITS Our field study area is around 120 square feet and we have excavated four trial pits of 6 feet length, 3 feet width and 3 feet depth. The soil samples have been taken from the following pits and the average properties of the black cotton soil have been tabulated. 6.3 PROPERTIES OF SOIL The average properties of black cotton soil in the site have been tabulated as follows Table 1 Properties of Black Cotton Soils 1 Specific Gravity Liquid Limit 65.4 % 3 Plastic Limit 38.5 % 4 OMC % 5 UCC Strength 1.28 kg/cm 2 6 Triaxial Cohesion 1.57 g/cm ANALYSIS OF STABILISED SOIL The trial pits were subject to stabilization using geo nails, yard waste and their combination. The time for stabilization was fixed as 45 days on consultation with geotechnical experts. The 10mm reinforcing bars were been used as agents for geonailing and felled leaves and shrubs available in the fields have been crushed and powdered to form stabilizing agents. Based on the results, the use of combined geonails and yard waste as soil stabilization agents were verified. The results of the soils stabilized by various means are presented as follows. Table II Properties of Non Stabilized Soils 1 Specific Gravity Liquid Limit 64.2 % 3 Plastic Limit 38.5 % 4 OMC % 5 UCC Strength 1.28 kg/cm 2 Table III Properties of Stabilized Soils using Geo Nails 1 Specific Gravity Liquid Limit 61.2 % 3 Plastic Limit 36.5 % 4 OMC % 5 UCC Strength 1.37 kg/cm 2 Table III Properties of Stabilized Soils using Yard Waste 1 Specific Gravity Liquid Limit 63.8 % 3 Plastic Limit 36.9 % 4 OMC 22.10% 5 UCC Strength 1.31 kg/cm 2 Table IV Properties of Stabilized Soils using Geonails and Yard Waste 1 Specific Gravity Liquid Limit Plastic Limit OMC UCC Strength 1.51 kg/cm 2 From the results, it can be confirmed that the soil stabilization had taken place by the effective use of the stabilizing agents. There has been a marked improvement in all the parameters by the combined use of geonails and yard waste. While the increase in UCC strength of the soil was just 6.56% and 2.87% by using geo nails and yard waste separately, their combined application resulted in an increase of %. Similarly there is a marked improvement in the consistency limits as well as improvement in the field properties like optimum moisture content and specific gravity. 20

6 VII. CONCLUSION Black Cotton Soils have been a boon for agriculture and a bane for construction. M/s Navrang Flyash bricks are in verge of setting an industrial shed at Andipalayam village which is fully of black cotton soil. Before setting up the industry, the company has planned to do soil stabilization and we are doing this research project. The use of waste materials to stabilize the soil and make it as strong and stable as any other soil is the primary objective of the project. For this, we need to choose admixtures that may help in stabilization. The use of waste materials as admixtures would be the best suitable option. The use of yard waste and geonails in combination may prove to be an ideal solution for increasing the strength of the soil and that too in a rapid manner. Geonails are good stabilizing agents, but they are not effective on clays due to poor bonding and softness of clay. Therefore yard waste is used as a catalyst to make the soil hard enough for intrusion by geonails, which would then impart high strength in quick time [4] Soil Groups in India - [5] Analysis of Engineering Properties of Black Cotton Soil and Stabilisation using Lime Kavish Mehta et al International Journal of Engineering Research and Applications May 2014 [6] Stabilisation of Black Cotton Soils Using Fly Ash, Hubballi Dharwad Municipal Corporation Area, Karnataka, India Udhayashankar D Hakari, C.Puranaik Global Issue of Researches in Civil Engineering February 2012 [7] Utilization of Copper Slag to improve geotechnical properties of soil, Thesis by Yogendra Tandel - SVNIT, Surat April 2008 [8] Effect of lime and fly ash on Engineering Properties of Black Cotton soil Bairwa Lamlakhan et al - International Journal of Emerging Technology and Advanced Engineering November 2013 The field study made at the plant vouched for the success of the combined application of geo nails and yard waste. The stabilization results show that the combined use of geonails and yard waste bring about an increase in nearly 18% in the shear strength of the soil while the maximum increase achieved was 6%, when used separately. Similarly the other properties like consistency limits, optimum moisture content and specific gravity were much improved when the geo nails were used in addition with yard waste. Thus the study vouches for the use of geo nails for the stabilization of black cotton soils and recommends the application of yard waste as an additional supportive agent for stabilization. REFERENCES [1] Geotechnical Engineering Office, Hongkong Guide to Soil Nail Design and Construction, CEDD Publications 2008 [2] Soil Stabilisation Principles and Practice O.G. Ingley John Wiley Sons, 2009 [3] Study of Geotechnical properties of black cotton soil stabilized by sawdust Arpita Patel National Conference on Recent Trends in Engineering and Technology 21