EXPERIMENTAL AND ANALYTICAL RESULTS OF FOOTINGS ON REINFORCED SAND BED

A reinforced soil is a soil bed carrying stiffer materials as reinforcement. The concept of reinforcing soil is an age old art. However, the technique is not fully exploited, as there are very few studies available pertaining to methods of design and analysis. Thus there is a need to understand soil-reinforcement interaction. Because the reinforcing action requires good frictional bond between the ties and the soil, only free draining granular soils are used in the present study with two types of geo-grids having different aperture size and thickness. This study was undertaken to expand the knowledge concerning reinforced earth by potential benefits of using reinforced earth slabs to improve the bearing capacity of granular soil. This paper presents the results of model tests with solid circular and ring footings resting on reinforce sand beds. The experimental study involves two series of tests. In both the series sand used was same with same relative density. In first series the laboratory model plate load tests were performed on a ring footing resting on sand bed reinforced with various sizes and with different number of geogrid Netlon CE-121. Pressure – settlement curves were plotted for all the test results and ultimate bearing capacity was calculated. The ultimate bearing capacity of reinforced sand was then compared with that of unreinforced sand by calculating a non dimensional parameter BCR. The second series of laboratory test concerns with the model plate load tests on solid circular and circular ring footings resting on sand bed reinforced with Netlon geo-grid CE-131. The ultimate bearing capacity was calculated after plotting the pressure – settlement curves for each experimental set of test. The experimental data obtained from the test series was analyzed and the increase in bearing capacity of sand reinforced with three number of geo grid-CE121 layers was found to be 318% at 7.5% settlement of the footing. The reduction in settlement of the footing was found maximum 90% for the sand bed reinforced with three number of geogrid-CE121 layers. The initial modulus for each test condition was determined and it was found that there a significant increase in initial modulus of reinforced sand as compared to that of unreinforced sand. The shape factor for ring footing is introduced to be included in Terzaghi’s bearing capacity equation.