Effect of sand layer on swelling of underlying expansive soil

Abstract

This research work is devoted to the study of the effects of the sand layer on the swelling of underlying expansive soil. The effects of different physical properties on the swelling of expansive soil have also been studied. The soil for the investigation has been collected from Savar and it has been mixed with bentonite to enhance its swelling potential. A bentonite to soil ratio of 1:3 has been selected for the present research. The swelling tests have been perfonned in conventional consolidometer. The investigation reveals that the effect of sand layer on the swelling of underlying expansive soil layer is significant. For a htiven surcharge pressure even a small thickness of sand bed on expansive soil reduces the amount of vertical movement al the top of the sand bed (footing level). It has also been found that a sand layer on expansive soil reduces the swelling pressure appreciably. It can be noted that under a given surcharge pressure, the amount of vertical movement at the footing level reduces with the increase of h/H ratio (h = thickness of sand layer and H = thickness of expansive soil layer). At low surcharge pressure, the effect of overlying sand bed is more pronounced . A sand bed of small thickness is effective in reducing the amount of vertical movement at the footing level at low surcharge pressure. This indicates that a sand bed between the floor slabs and expansive soil layer may be helpful in eliminating undesirable cracks of the floor slabs. From the study of the effect of thickness of expansive soil layer (without any sand bed on it), it has been fOlUldthat both the swelling pressure and (%) volume change for a given surcharge pressure are independent of thickness of expansive soil layer. For a particular thickness of expansive soil, the amount of (%) volume change dccrcascs with the incrcasc of sw-dmrgc pressure on it. It may be noted that although thc (%) volume changc does not changc with the thickness of expansive soil layer, the amolll1t of total vertical movement reduces due to the reduction of layer thickness. This indicates that partial removal of expansive soil layer will not eflect either the swelling pressure or the (%) volume change lmdcr a certain surcharge pressure on it , but it may help in reducing the total amount of vertical movement. This result is very much in a!,'Teement with the results of Chen (1975) and Kassi IT& Baker ( 1971 ).