IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613
Effect of Geo-Grid Reinforcement on Load Carrying Capacity of a Coarse Sand Bed Ayush Bhardwaj1 Vinod Kumar Mishra2 Subodh Kumar Jha3 1 P.G. Student 2,3Resident Engineer 1,2 Department of Computer Engineering 1,2 Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal 2MSV International INC Abstract— A series of plate load test are conducted on a coarse sand bed reinforced with geogrid compacted to a relative density of 50%. Footing plate having diameter of 60 mm is used in the shallow foundation. For the horizontal reinforcement layer circular geogrids of diameter 120 mm are used. Spacing and number of geogrids are varied in this study. A huge amount of improvement is observed in the bearing capacity of loose coarse sand bed on introduction of geogrid. A further improvement is seen in the bearing capacity on increasing the number of geogrid. Key words: Geogrid; Reinforcement; Coarse Sand; Bearing Capacity I. INTRODUCTION The most researched area in geotechnical engineering is ground improvement. There are various types of ground improvement techniques which are been employed, depending upon the ground conditions. Mechanical stabilization, granular piles, thermal stabilization, stabilization with various chemicals and concrete or bitumen reinforced earth are some of the ground enhancement techniques. A newer material Geotextiles, geofabrics and geogrids are being used as a reinforcement components for improving bearing capacity of poor soils. II. LITERATURE SURVEY A theoretical analysis for finding the pressure intensity of an isolated strip footings resting on reinforced earth slab for a specific settlement was conducted [1]. Model tests on strip footings on sand fill were conducted, with and without reinforcements [7]. A model plate load tests on uniformly graded sand and un-reinforced sand reinforced with layers of different type of geotextiles were conducted [3]. These tests concluded that bearing capacity depends on ratio of depth at which geotextile is placed below the footing of the first layer of reinforcement to the width of the footing), s/b (ratio of vertical spacing of the layers of geotextile reinforcement to the width of the footing) and number of reinforcing layers. Tests on strip footing resting on loose sand overlying weak clay with geotextile placed at sand-clay interface were carried out [5]. These tests resulted an increase in bearing capacity when distance of footing from geotextile layer was reduced and embedment depth is increased. Based on laboratory experiments two modes of foundation collapse were suggested, one associated with reinforcement slip and the other associated with tensile failure of reinforcement [6]. Studies on the improvement in bearing capacity of footings resting on granular bed overlying soft clay assuming a punching shear failure mechanism in the foundation soil were carried out [8]. Confining effect is generated due to geogrid reinforcement. A new model is generated which represents the granular bed
over the soft clay deposit [9]. Many laboratory model and tests were carried out earlier to simulate the behavior of reinforced soils. They provide a good understanding of reinforced soil behavior. III. EXPERIMENTAL INVESTIGATION For preparing the test sand beds dry coarse sand is used. Compaction of test sand beds to a thickness of 200 mm in a test tank of cylindrical shape of diameter 300 mm and height of 250 mm (Fig 1). Constant relative density of 50% are kept for all the sand beds. The compaction of sand bed to a dry unit weight (γd) which corresponds to the fixed relative density of 50% is done. Dry unit weight (γd) which corresponds to Dr = 50% is resolute through plate tests conducted on all sand types by defining the void ratios in their densest and loosest states, namely, emax and emin. By presetting the relative density at 50%, the void ratio which corresponds to this relative density is determined. Compaction of sand bed is done in four layers, thickness of each layer being 50 mm. e weight of dry sand that corresponds to the cubic measure weight is realized and divided in to four equal components. Each half is compacted within the take a look at tank to a most thickness of fifty millimeter. Within the case of geogrid reinforcement sand beds, the geogrid layers were placed at the specified height, u and spacing, s. The thickness of all the sand layers was checked so as to make sure the prefixed cubic measure weight. A foundation plate or test plate of diameter 60 mm was used for the conduct of the plate load tests. The diameter is kept constant at 120 mm in all the test. The number of geogrids is varied as n = 1, 2 and 3. The spacing between the geogrid is kept constant as 10 mm. Netlon CE 121 is used for providing horizontal geogrid reinforcement in the sand base. It has an aperture size of 6 mm made of high tensile polypropylene sheet. After the compaction, the test plate is kept on the sand bed at the center of the tank and subjected to loading. Two dial gauges of 0.01 mm sensitivity are fixed to the test plate for observing the deformation under the applied loads. Initially, a seating load of 10 N is applied on the test plate. The subsequent load increments are shown in Table 1. Each load increment is kept on the sand bed for 60 minutes and the deformations are observed. The mean of deformation values observed in the two dial gauges is reported as the actual deformation.
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Effect of Geo-Grid Reinforcement on Load Carrying Capacity of a Coarse Sand Bed (IJSRD/Vol. 4/Issue 05/2016/339)
Load (N) Test case 30 Unreinforced 30 Unreinforced 30 Unreinforced 30 Unreinforced 40 Unreinforced 40 Unreinforced 30 Reinforced 30 Reinforced 30 Reinforced 30 Reinforced 40 Reinforced 40 Reinforced 40 Reinforced 40 Reinforced Table 1: Load increment cases Fig. 1: Cylindrical test tank IV. RESULTS AND DISCUSSIONS
V. CONCLUSION The geogrid reinforced sand beds results in improved load – settlement behavior representative of higher bearing capacity resultant of geogrid reinforcement. The geogrid reinforced sand layer is more effective when placed in a closer propinquity to the base of the foundation. The load reaction was better for u = 10 mm than u = 20 mm. When the spacing between the geogrids is less, the compressive load response was further improved. The load-settlement curve for n = 3 was lying above all other curves indicating highest improvement in load carrying capacity. The curves for n = 2 and n = 3, in that order, lay below that for n = 3. The load required for δ = 0.5 mm increased with increasing number of geogrids. REFERENCES
Fig. 2: Load settlement behavior of unreinforced coarse sand be with single geo grid Fig 2 shows the load-settlement behavior of unreinforced coarse sand bed and coarse sand bed reinforced with single geogrid (n=1) placed at u = 10 mm and u = 20 mm. Fig 3 shows load-settlement behavior of unreinforced coarse sand and coarse sand reinforced with various configurations of geogrids (n = 2; s = 10 and n = 2; s = 20) for u = 10 mm. When the spacing between the geogrids was less, the compressive load response was further improved.
Fig. 3: Load settlement behavior of unreinforced coarse sand be with varying number of geo grid
[1] Binquet, J. and Lee, K.L., (1975), Bearing capacity analysis of reinforced earth mass, Journal of geotechnical engineering division, ASCE, 101(GT12), pp.1241- 1255 [2] Binquet, J. and Lee, K.L., (1975), Bearing capacity test on reinforced earth slabs, Journal of technical engineering division, ASCE,.101(GT12) pp.1257- 1276 [3] Guido, V.A., Biesiadecki, 0.1. and Sullivan, M.J., (1985), Bearing capacity of geotextile reinforced foundation, Proceedings of 11th International Conference on Soil Mechanics and Foundation Engineering, 3, pp. 1777-1780. [4] Guido, V.A., Chang, D.K. and Sweeney, M.A., (1986), Comparison of geogrid and geotextile reinforced earth slabs, Canadian Geotechnical Journal, 23, pp. 435-440. [5] Kim, S.I. and Cho, S.D., (1988), An experimental study on the ‘cntribution of géotextiles to bearing capacity on footings on week clays, Proceedings of the International Geotechnical Symposium on Theory and Practice of Earth Reinforcement, pp. 215-220. [6] Michalowski, R.L. and Viratjandr, C., (2005), Twolayer reinforced foundation soils loaded to failure, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 130, pp. 38 1-390. [7] Ramaswamy, S.D. and Yong, K.Y., (1983), Cyclic load tests on the reinforced foundation sand beds, Proceedings 8th European Conference on Soil Mechanics and Foundation Engineering, pp. 527-530.
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Effect of Geo-Grid Reinforcement on Load Carrying Capacity of a Coarse Sand Bed (IJSRD/Vol. 4/Issue 05/2016/339)
[8] Sidramappa Shivashankar Dharane. RCC Beam with Spiral Reinforcement, International Journal of Civil Engineering and Technology, 5(8), 2013, pp. 98– 100. [9] Ramu, K., Madhav, M.R. and Poorooshasb, H.B., (1999), Finite strain theory for response of granular bed overlying soft ground, 4thAsia-Pacific Conf. on Computational Mechanics, Singapore.
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