INFLUENCE ON BEARING PRESSURE OF SHALLOW FOOTING RESTING ON GEOGRID REINFORCED DOUBLE LAYERED SOIL SYSTEM

J. Sudheer Kumar, Love Sharma

Abstract: Model test was conducted to investigate the effect of geogrid reinforcement on bearing pressure of strip footing resting on sand overlay on clayey soil stabilized with fly ash. Various percentages of fly ash mixed with clayey soil and found the optimum proportion. The optimum percentage of fly ash mixed with clay and then used as a second layer in the model test. Experiments were conducted on model test of strip footing, calculated the bearing pressure of double layer soil system without geogrid, with geogrid at the interface level and at designated levels within the sand layer. To check the different parameters contributing to their performance using model test of tank size is 830mm x 680mm x 630mm. The parameters investigated in this study include H/W (thickness of top sandy layer to width of footing), x/W (depth of the 1st layer of geogrid to width of footing), d/W (spacing between consecutive geogrid layers to width of footing), l/W (length of the geogrid layer to width of footing). The effect of different H/W ratios and no. of geogrid layers (n) on the bearing pressure ratio (BPR) and settlement reduction ratio (SRR) were investigated. Based on the Atterberg’s limit the optimum mix obtained is 90% clay and 10% fly ash. The optimum mix was used as bottom layer in the model tank. The result indicates that bearing pressure increases with increasing the H/W ratio and n values. The bearing pressure calculated without geogrid at three different materials like clay alone, optimum mix of clay and fly ash and double layers (sand, optimum mix of clay and fly ash) are 104.1, 106.8 and 187.5 kN/m2 respectively. Geogrid reinforcement used at the interface (n=1) and at two different levels within sand layer (n=2, 3), the corresponding bearing pressure values are 270 kN/m2 , 315 kN/m2 and 636.7 kN/m2 respectively. The bearing pressure for the soil increases with H/W = 0.5, 1, 1.5 and 2, the average values are 12.35%, 35.76%, 75.56% and 230.83% respectively. It was found that the use of geogrid at interface and multiple layers has a considerable effect on the bearing pressure. Use of geogrid layers in the granular overlay has significant effect on Bearing pressure ratio (BPR) & Settlement reduction ratio (SRR).

Keywords: Model test, optimum mix, geogrid, bearing pressure, SRR.

DOI: https://doi.org/10.15623/ijret.2017.0607015