BEARING CAPACITY OF FOUNDATIONS ON WEAK SOILS REINFORCED WITH GEOSYNTHETICS

Abstract

A weak soil needs to be reinforced in order to take up the loads transmitted by heavy structures. The inclusion of geosynthetics as reinforcement enables the soil to support substantial tensile loads at defined deformations over extended design lives. in the present study, the plate-load tests were carried out in laboratory on sand reinforced with geogrids. A mild steel square footing of size 10 cm x 10 cm with 1 cm thickness was used in a tank of size 53.5 cm x 53.5 cm with 60 cm depth which was tilled with poorly graded solani sand at relative density of 60% with dry unit weight as 15.25 kN/m3. The HDPE geogrid of tensile strength 7.68 kN/m was used as reinforcement which had aperture size of 8 mm x 6 mm. Loads were applied in small increments and deformations were noted. A parametric study was carried out to investigate the effects of various parameters on the bearing capacity of reinforced soil such as the the width of reinforcement layers, depth of top layer of geogrid from the base of footing, number of geogrid layers and vertical spacing between the layers. The optimum width of geogrid was found to be 3.513 where B is the size of square footing. The optimum value of depth of top layer of reinforcement from the base of footing was found to be 0.313 and optimum number of layers was found to be 4. The optimum uniform spacing between the geogrid layers was found to be 0.213. In order to optimize the widths of geogrids at various levels, a study was conducted by placing the geogrids of different widths at different depths. It was found that widths of 2B, 2.5B, 3B and 3.513 for the 4 layers from top to bottom will give the nearly same results as 3.5B width of each layer. Hence a great economy can be achieved by this technique of different widths of reinforcement layers at different depths in the projects employing geogrids. The effect of non-uniform spacing between geogrids layers was also investigated. However, the results of this non-uniform spacing arrangement were found to be somewhat less than uniform spacing. At the last, the deformations of geogrid layers after settlement failure stage was noted and they were found to resemble a bowl shape contributing membrane effect to the reinforcement mechanism. Tests were also conducted on reinforced sand with different relative density and the bearing capacity or of reinforced sand was found to be increasing with increase in relative density.