EFFECT OF NATURAL GEOTEXTILE ON UNPAVED AND PAVED ROAD MODELS- A COMPARATIVE STUDY

Transcription

1 INDIAN GEOTECHNICAL CONFERENCE EFFECT OF NATURAL GEOTEXTILE ON UNPAVED AND PAVED ROAD MODELS- A COMPARATIVE STUDY P.T. Abdul Azeez 1, M.K. Sayida 2, Y. Sheela Evangeline 3 ABSTRACT The development of cracks and ruts which decrease the serviceability of pavement are the external indicators of pavement deterioration caused by repeated loading, environmental factor, improper drainage or combination of thereof. ith the repeated application of traffic loading, there deformations degrade the pavement and irregularities, ruts, longitudinal asphalt cracks, alligator cracks etc. appear on the surface. Maintaining the pavement structure at good serviceability level in the problematic regions is a major challenge faces by the concerned departments. The structural strength of flexible pavement is related to its constitutive elements such as the insitu subgrade, the granular base and bituminous layer. Geosynthetics are commonly used now a day to improve the performance of both paved and unpaved roads by inserting them typically at the interface between the subgrade and base course or in between the pavement layers. The term geosynthetic is used to describe a group of materials in which geotextiles are used in the broad cast range of civil engineering applications. In this study coir geotextiles are used as reinforcement, separation or drainage layer in unpaved or paved road models. Coir geotextiles, formed by weaving coir fibre, can extensively used for various geotechnical engineering application. No small scale model plate load tests were reported in the literature using natural geotextiles on paved road sections where as few studies were reported on unpaved road sections. The objective of this study is to investigate and understand the influence of coir geotextiles on the strength and deformation characteristics on unpaved and paved road models. To determine this, paved and unpaved road sections prepared and tested with and without coir geotextiles placed at two locations in the pavement section. oven coir geotextiles having a gsm of 1269 and a nonwoven geotextile having gsm 4 were used for the study. The pavement sections were a three layer system consists of subgrade prepared by the soil taken from a periodically distressed location, and pavement layers of granular base (et Mix Mecadam) and surfacing course (Dense Bituminous Macadam & Bituminous Concrete) prepared as per the IRC specifications. To prepare reinforced sections, geotextile was placed at the base/subgrade interface in unpaved and paved pavement models. All the tests were performed in a circular tank and static and repeated loads were applied through a circular plate by rotating the wheel of a screw jack. Static and repeated loads were applied on unreinforced and reinforced pavement sections with woven and nonwoven coir geotextiles. The performance were analysed in various behavior such as Bearing Capacity, Percentage Reduction in Settlement (PRS) and Traffic Benefit Ratio (TBR). The results indicate that the 1 Assistant Director, Kerala Highway Research Institute, Trivandrum, Kerala, India, ptabdulazeez@hmail.com 2 Associate Professor, College of Engineering, Trivandrum, Kerala, India, sayidamk@rediffmail.com 3 Associate Professor, College of Engineering, Trivandrum, Kerala, India,sheelabala@gmail.com

2 Abdul Azeez P.T., Sayida M.K., Sheela Evangeline coir geotextiles increase the load carrying capacity and reduce permanent deformations on Unpaved and Paved road sections under repetitive loads. The maximum benefits obtained when the coir geotextiles used on the paved road section than unpaved section. Keywords: Coir Geotextile, Unpaved road Paved road, Bearing Capacity, Plastic deformation

3 INDIAN GEOTECHNICAL CONFERENCE EFFECT OF NATURAL GEOTEXTILE ON UNPAVED AND PAVED ROAD MODELS- A COMPARATIVE STUDY P.T. Abdul Azeez, Assistant Director, Kerala Highway Research Institute, Trivandrum, Kerala, ptabdulazeez@gmail.com M.K. Sayida, Associate Professor, College of Engineering, Trivandrum, Kerala, sayidamk@rediffmail.com Y. Sheela Evangeline, Associate Professor, College of Engineering, Trivandrum, Kerala, sheelabala@gmail.com ABSTRACT: Coir geotextiles can extensively used for various geotechnical engineering application. No small scale model plate load tests were reported in the literature using coir geotextiles on paved road sections where as few studies were reported on unpaved road sections. Static and repeated loads were applied to investigate the influence of coir geotextiles on laboratory pavement section. The performance were analysed in various behavior of pavement sections. The results indicate that the coir geotextiles increase the load carrying capacity and reduce permanent deformation on pavement sections. The maximum benefits obtained when the geotextiles were used on the paved road section than unpaved section. 1. INTRODUCTION Pavement failure is defined in terms of decreasing serviceability caused by the development of cracks and ruts. Pavement distresses are external indicators of pavement deterioration caused by loading, environmental factor, improper drainage facilities, construction deficiencies, or combination of thereof. The majority of pavement distress can be categorized as surface distress of deformation or cracks, or a combination of these three. The traffic of vehicles on the surface of roads yields deformations in the pavement structure that are a function of both the travelling loads and mechanical characteristics of the pavement itself. These deformations are either reversible (elastic deformation) or permanent (plastic ruts). ith the cyclic application of traffic loading there deformations degrade the pavements and irregularities, ruts, longitudinal asphalt cracks, alligator cracks appear on the surface. The structural strength of flexible pavement is related to its constitutive elements such as the bituminous layer, the granular base, the in-situ subgrade soil etc. Geosythetics are nowadays, commonly used to improve the performance of both paved and unpaved roads by inserting them typically at the interface between the aggregates base course and the subgrade or between the pavement layers. The term geosynthetic is used to describe a group of materials which include geotextiles, goegrids, genets, geomembranes, geosynthetic clay liners etc. of these materials, geotextiles are used in the broad cast range of Civil Engineering applications. Coir geotextiles, formed by weaving coir fibres, can be extensively used for various geotechnical engineering applications. Coir geotextiles, which are formed from the husk of coconut have high lignin content which makes them the most strongest and durable fiber. In this study, it was intended to conduct the performance of natural geotextiles (coir) placed in layers on laboratory models of unpaved and paved road section of a selected distressed location to determine the Bearing Capacity, Percentage Reduction in Settlement(PRS), Traffic Benefit Ratio(TBR) and Rut Reduction Ratio (RRR). Soil sample collected from a periodically distressed road location at Aryanad-Palode road in Thiruvananthapuram District of Kerala for the study. Two types of natural geotextiles one woven designated as and the other one non woven designated as N are selected for the study on the laboratory pavement models.

4 Abdul Azeez P.T., Sayida M.K., Sheela Evangeline 2.LITERATURE REVIE Geosynthetic reinforcement is one of the established techniques of ground improvement for over years. Since 197s, geosynthetics have been used to improve the performance of both paved and unpaved roads. For these applications, geosynthetic sheets are placed at the subgrade-base interface or within the base course to increase bearing capacity of subgrade or provide confinement to base courses. Geotextiles extend the service life of the roads, increase their load carrying capacity and reduce rutting. The major functions of geotextiles are separation, filtration, drainage and reinforcement. In transportation application, separation usually refers to the geotextile s role in preventing the intermixing of two adjacent materials. For example by separating fine subgrade soil from the stone which comprised a roads base course, the geotextiles preserves the drainage and strength characteristic of the aggregates material. The plastic surface deformation of unpaved road under repeated loading was greatly reduced by the inclusion of coir geotextiles within the base course pavement irrespective of base course thickness [1]. The performance of coir geotextiles in separation and filtration function has improved with the increase in the thickness of gravel layer [1]. The efficiency of the geosynthetic as a reinforcement in a road can be quantified by the Traffic Benefit Ratio Values of Traffic Benefit Ratio (TBR) varied depending on the type of reinforcement and loading stage considered, with the largest value in each loading stage having been observed for the geogrid reinforced road [2]. The mechanical properties of the geosynthetics used for pavement applications are improved under the confinement provided by the soil. The improved performance of geosynthetic-reinforced pavements can be attributed to lateral restraint mechanisms [7]. The load-carrying capacity of lateritic subgrade reinforced with coir geotextile is improved in Monotonic plate load test and the percentage reduction in settlement varies from7% to 57% [9]. The coir geotextiles improved the Percentage Reduction settlement (PRS) and Resilient Modulus and Traffic Benifit Ratio (TBR) of the unpaved roads under repeated loading [8]. 3.MATERIALS USED FOR THE STUDY The pavement section selected for the study was a three layer system. It consists of a subgrade layer, a base course layer and a surface course. 3.1 Subgrade Soil Soil for the test was collected from a periodically distressed road location at chainage / on Aryanad-Palode road in Thiruvananthapuram District for the study. The basic soil properties were tested and were classified as ML (Inorganic silt of low plasticity) as per Indian standards. The properties of soil used in the present study are given in Table 1. Table 1 Characteristics of soil used for the study Sl. No. Properties of Soil Values 1 Specific Gravity Grain Size Analysis a Gravel (%) 5. b Coarse Sand (%) 11.9 c Medium Sand (%) 19.5 d Fine Sand (%) Hydrometer Analysis a Silt (%) b Clay (%).67 4 Atterberg Limits a Liquid Limit (%) 27.7 b Plastic Limit (%) NP c Shrinkage Limit (%) Compaction Characteristics a Optimum Moisture Content (%) b Maximum Dry Density (g/cc) CBR value (%) (Soaked) Base Course Layer-et Mix Macadam et Mix Macadam(MM) was selected as base course layer. It consists of clean crushed graded

5 INDIAN GEOTECHNICAL CONFERENCE aggregates premixed with other granular materials (IRC 19, 1997). The aggregate used for MM was in specified gradation as per Ministry of Road Transport and Highways (MORTH) Specifications for Road and Bridge orks (5 th revision) 13 published by Indian Road Congress (IRC). Five types of aggregates (45 mm, 24 mm, 12 mm, 6 mm and filler) used in a proportion of 15::3:3:5 to get the required gradation. The OMC of MM was 5.25% and MDD is 2.3 g/cc. Fig. 1 shows the Gradation chart of et Mix Macadam % Finer Particle size (mm) Fig. 1 Gradation chart of et Mix Macadam 3.3 Bituminous Layers The bituminous layers consists two layer, one was a base course of Dense Bituminous Macadam (DBM) and other one was a surface course of Bituminous Concrete (BC) Dense Bituminous Macadam (DBM) The Dense Bituminous Macadam was prepared as per IRC 94, The proportion of the aggregate obtained as per the grading requirement in Table 5-1 of MORTH specification (5 th revision 13). Five types of aggregates used (19 mm, 12 mm, 6 mm, 4 mm and crusher dust) to get the required gradation of :11:22:18:29. Fig.2 shows the gradation chart of aggregate used for DBM. The aggregate impact value.79 %, Los Angeles Abrasion Value % and Combined Flakiness and Elongation Index % are the physical properties of the aggregates used. The Optimum binder content is 4.5 % and the Density of the mix is 2.47 g/cc. % Finer Fig. 2 Gradation chart of DBM Bituminous Concrete (BC) The Bituminous Concrete was prepared as per IRC 29, Four types of aggregates used (12 mm, 6 mm, crusher dust and filler) to get the required gradation of 18:17:41:24. Fig. 3 shows the gradation chart. The aggregate impact value 23.5 %, Los Angeles Abrasion Value 25.38% and Combined Flakiness and Elongation Index % are the physical properties of the aggregates used. The optimum Bitumen content is 5.45% and the Density of mix is 2.42 g/cc. % Finer 1 Particle size (mm) Particle size(mm) Fig.3 Gradation chart of Bituminous concrete

6 Abdul Azeez P.T., Sayida M.K., Sheela Evangeline 3.4 COIR GEOTEXTILE One woven and one non-woven coir geotextiles were used for the study. Fig. 4 shows the types of geotextiles used for the study. The physical and engineering properties of coir geotextiles used for the study are presented in Table 2. Particulars Table 2 Properties of coir geotextiles Unit oven () Nonwoven (N) Mass/unit area g/m Thickness mm Opening size mm x mm 6 x Tensile strength arp kn/m ept kn/m oven Nonwoven Fig. 4 Coir Geotextiles 4. LABORATORY TEST SET UP The experiments were conducted in a circular tank of mm in diameter and mm deep made up of 3 mm thick MS plate. The settlement of the plate was measured using two dial gauges, fitted on the plate on either side of the loading shaft. Fig. 5 & 6 shows the schematic diagram of the test set-up. The settlement was measured by taking the average of two dial gauge readings. Load was applied through a circular plate, 1 mm in diameter and 25 mm thick. The vertical load was applied on the plate through screw jack having 15 T capacity using a proving ring of 5 kn capacity held in the reaction frame. The thickness of subgrade soil was 25 mm. The soil was filled in the tank in 5 layers, each layer having 5 mm thickness. Soil required for each layer was mixed with required amount of water and was filled in tank in Maximum Dry Density and Optimum Moisture Content. The parameters to be varied are type of geotextiles, stress applied and pavement layers. The plate diameter and thickness of layers were scaled to a factor of 2/5 with respect to a full scale wheel load size of 3 mm since the diameter of the plate used for the test is 1 mm. Unpaved section was constructed with base course thicknesses of mm to represent pavement

7 INDIAN GEOTECHNICAL CONFERENCE sections of 15 mm (75 mm Sub base + 75 mm base) at distressed location. The paved sections were constructed with base course thicknesses of mm, bituminous base layer mm to represent 5 mm layer and bituminous surface layer 12 mm to represent 3 mm layer. To prepare reinforced sections geotextile was placed at the base/subgrade interface in pavement section. Since the width of the geotextile roll was equal to the internal width of the test tank a single piece of geotextile was used to cover the entire surface of the test section. Fig. 5 Experimental test setup of Unpaved section (a) Schematic Diagram (b) Lab setup Fig. 6 Experimental test setup of Paved section (a) Schematic Diagram (b) Lab setup 5 TEST PROCEDURE Static and repeated load tests were done on the prepared pavement system. The monotonic tests were done for Subgrade, Unpaved and Paved section, in order to find the ultimate bearing capacity of the unreinforced section. The permissible bearing pressure was assumed as % of ultimate bearing capacity. The repeated load tests were done by giving this % permissible load repeatedly for cycles. 5.1 Static Load Test Static plate load test were first done in order to find the bearing capacity of subgrade soil, Unpaved and Paved road sections. Monotonic load tests were conducted on test sections as per Indian Standards (IS 1888, 1982). The test bed was leveled and the footing was placed centrally over it. Load was applied by rotating the wheel of the screw jack manually. A seating pressure of 7 kpa was applied. Dial gauge readings were taken at every load increments of.3 kn. Each load increment was applied when the settlement became less than.25 mm/min. 5.2 Repeated Load Test The repeated load testing was done on both unreinforced and reinforced pavement section. The tests were conducted on two types of test sections with Unpaved and Paved one. To investigate the influence of coir geotextile reinforcement on the behaviour of the pavement section under repeated loading, cycles of load were applied on both sections. The geotextiles were placed at the interface between subgrade and base course (MM). The unpaved road sections were tested with a stress intensity of 3 kpa and paved road section were tested with a stress intensity of kpa. The stress level corresponded to % of strength of pavement under static load tests. Sl. No. Test Section Table 3 Test Series Position of Type of Geotextile loading NA 2 Paved *Control Specimen NA 1 Unpaved Subgradeinterface Base Subgrade-Basinterface Static Type of Geotextile CS* Repeated oven & Nonwoven Static CS* Repeated oven & Nonwoven

8 Abdul Azeez P.T., Sayida M.K., Sheela Evangeline Pressure on the footing is increased from zero to the required level by rotating the wheel at a frequency of 3 rotations per minute. The maximum desired pressure is applied for 1s and then load is released to zero. The period of rest for the section was also maintained as 1s in all the tests. cycles of load were given to all the test sections. 6. RESULTS AND DISCUSSION 6.1 Static Load Test Monotonic load tests were conducted on subgrade soil and pavement sections. Fig. 7 shows the relationship between the bearing stress and settlement of the subgrade, unpaved and paved road sections in soaked condition. The subgrade soil failed at a bearing pressure of 193 kpa in soaked condition and which are 55 kpa and 7 kpa in the case of Unpaved and paved section respectively. Settlement (mm) Bearing pressure (kpa) 5 15 Subgrade Unpaved section Paved section Fig. 7 Bearing pressure - settlement graph of unreinforced sections (soaked) 6.2 Repeated Load Test Repeated load tests were conducted on Unpaved and Paved pavement sections with and without coir geotextile. Minimum cycles of load were given for each section with and without coir geotextile. Fig. 8 and 9 shows the variation of settlement with respect to the number of load cycles repeated for Unpaved (Stress = 3 kpa), and Paved (Stress = kpa) road sections respectively. It is clear from the figure that when the coir geotextile is used as an interface layer between subgrade and base course of unpaved and paved road section, the strength of the section increased and the settlement decreased. Settlement (mm) Fig. 8 No. of load repetitions settlement graph- (Unpaved road section) The settlement reduced up to 58% in the case of oven and 29% for Nonwoven coir geotextile reinforced unpaved sections. Settlement(mm) Numbers of repetitions 5 Number of repetitions Fig. 9 No. of load repetitions settlement graph (Paved road section) The settlement reduced up to 86% in the case of oven and 53% for Non woven coir geotextile reinforced paved sections. This trend of settlement behaviour has a direct relation with the tensile strength of the coir geotextiles. CS N N CS

9 INDIAN GEOTECHNICAL CONFERENCE Plastic deformation is found to be reduced due to the introduction of coir geotextile reinforcement. Placement of a geotextile layer in the base course allows for shear interaction to develop between the aggregate and the geotextile as the base attempts to spread laterally. Shear load is transmitted from the base aggregate to the geotextilee and places the geotextile in tension which retards the development of lateral tensile strain in the base adjacent to the geotextile. Smooth interface between soft subgrade and geotextile placed at the interface of base and subgrade results in a decrease in the percentage reduction of plastic deformation Percentage Reduction in Settlement The percentage reduction in settlement (PRS) is defined as shown below PRS = Su Sr x Su here, Su = the settlement of unreinforced soil corresponding to its ultimate bearing capacity. Sr = the settlement of reinforced soil corresponding to ultimate bearing pressure of unreinforced soil. The Percentage reduction in settlement of each geotextile with respect to the control specimen at,,, and cycles of loading are shows in Fig. 1 &11. PRS No. of loadcycles (1) Fig. 1 Comparison of PRS at various load cycles (Unpaved road) N The first series of unreinforced Unpaved section is compared with reinforced section with coir geotextiles and in the second series, unreinforced Paved section is compared with reinforced section. PRS No. of cycles Fig. 11 Comparison of PRS at various load cycles (Paved road) The Percentage Reduction in Settlement of each geotextile with respect to the control specimen at cycles of loading in Unpaved and Paved section is shown in Fig. 12. PRS Unpaved Road section Paved Fig. 12 Comparison of percentage reduction in settlement in unpaved and paved pavement sections. N Seri es1 N

10 Abdul Azeez P.T., Sayida M.K., Sheela Evangeline Rut Reduction Ratio No. of cyles Fig. 15 Comparison of RRR at various load cycles (Paved section) RRR Geotextile N Fig. 16 Comparison of RRR with geotextiles at load cycles in pavement sections. The reinforced section with a lower RRR value is better in terms of performance improvement. The oven geotextiles shows the lower RRR value among the geotextiles used. The maximum benefit obtained when the geotextiles placed in paved road section. 7 CONCLUSIONS The following conclusion can be drawn from the test results of the present investigation. In the repeated load test, when coir geotextile is used as an interface layer between subgrade and base course, the strength of the section increased and the settlement decreased compared to the unreinforced section. oven coir geotextiles having a gsm of 1269 () has higher reduction in settlement for N Unpaved Paved unpaved and paved road section. Compared to the unreinforced road section the maximum Percentage Reduction in Settlement of Unpaved and Paved sections are 77% and 9% respectively. The Traffic Benefit Ratio is highest for oven geotextile in all cases of loading. Hence it can be concluded that woven geotextiles excels in the application of unpaved, paved road sections. The TBR values are more in paved road section than unpaved section. The coir geotextile significantly decreased the permanent vertical deformation over the loaded area of the pavement under repeated loading by restraining the laterall spreading of base material. Based on the above findings, it can be concluded that the use of Coir geotextiles in unpaved and paved roads are very promising and should be promoted. But it should be noted that the present experimental results are based on the tests conducted on small scale laboratory tests. Although, the results of this study may be somewhat different to full-scalthe test behaviour in field, but the general trend may be similar. REFERENCES [1] E.A. Subaida, S. Chandrakaran, N. Sankar (9). Laboratory performance of unpaved roads reinforced with woven coir Geotextiles, Journal of Geotextiles and Geomembranes, 27, pp [2] Ennio M. Palmeira, Luiz G.S. Antunes (1). Large scale tests on geosynthetic reinforced unpaved roads subjected to surface maintenance, Journal of Geotextiles and Geomembranes, 28, pp [3] IS 1888 (1972). Guidelines for Plate Load Test. [4] IRC 19 (1997). Guidelines for et Mix Macadam. [5] IRC 94 (1986). Specification for Dense Bituminous Macadam. [6] IRC 29 (1988). Specification for Bituminous Concrete (Asphaltic Concrete) for road pavement.

11 INDIAN GEOTECHNICAL CONFERENCE [7] Jorge G. Zornberg (11). Advances in the use of geosynthetics in pavement design Geosynthetics India 11, September 11, IIT Madras, Chennai. [8] Juhi Singh, Sayida M.K. (13). Effect of Coir Geotextiles on the Bearing Capacity of Unpaved Roads, Proceedings of 14 th National Conference on Technological Trends (NCTT 13), pp [9] Nithin S., Sayida M. K., Sheela Evangeline (12). Improving the Bearing Capacity of Lateritic Subgrade using Coir Geotextiles, Proceedings on National Conference on Technological Trends. [1] Rajagopal, Ramakrishna (9), Coir Geotextiles as Separation and Filtration Layer for Low Intensity Road Bases, 9, Guntur, India, pp