Collapse of stone column foundations due to inundation.

An important problem encountered by foundation engineers involves partially saturated soils which possess considerable in-situ dry strength that is largely lost when the soils become wetted. Foundation design in such soils is difficult at best. In many cases, deep foundations may be required to transmit foundation loads to suitable bearing strata below the 'collapsible' soil deposit. This research has studied the behaviour and performance of stone columns confined and not confined by geofabrics and rigid piles, as deep foundations, in collapsible soil subjected to inundation. Laboratory tests were carried out, under controlled conditions of sand density and surcharge pressure, using six different types of foundation supports (a sand column, sand columns confined by T700, T1000, T1500 or T2000 geofabrics and a rigid pile). Each type of foundation was considered in three different lengths 250 mm, 300 mm and 410 mm. This work consisted of installing and loading 'model' foundations into a stress controlled pot containing a collapsible soil and allowing a slow rise of the water level inside it. The tests were designed to investigate the efficiency of these types of foundation supports on the improvement of the carrying capacity and on the reduction of settlement of the ground. The reduction in vertical compression of the 'piles' was also studied analytically using an analytical approach adopted and developed from models applied to soft soils. The experimental results are compared with analytical predictions. The comparisons show that the reduction in vertical compression of the 'pile' is governed by its stiffness and its length. These variables are of prime importance in the general performance of the 'pile'.