Drag Load on End-Bearing Piles in Partially Saturated Collapsible Soil

Collapsible soils are categorized as problematic soils, which display high shear strength when they are dry or at a low degree of saturation, and experience large and sudden deformation and lose of strength when inundated. End-bearing piles are often employed to penetrate these layers to transfer the structure load to a deeper stronger stratum. In the literature, reports can be found dealing with negative skin friction acting on pile's shaft due to full inundation. However, the case of partial saturation has received little attention. This paper presents the results of an experimental investigation on an end-bearing pile resting on strong soil strata and surrounded with partially saturated collapsible soil. The objective of this paper is to evaluate the drag load acting on the pile's shaft for a given collapse potential and degree of saturation. In this analysis, the soil matric suction plays an important role in predicting the drag load developed on the pile's shaft during wetting. The experimental set-up was designed to measure the drag load acting on the pile's shaft penetrating partially saturated collapsible soil, subjected to a degree of saturation of 25% up to 100%. The material used in this investigation was a laboratory prepared collapsible soil, consisting of a mixture of fine sand and kaolin clay at water content of 5%. Results showed that the drag load increases with the increase of the collapse potential, the degree of saturation, and the inundation pressure. Design procedure is provided to predict the drag load acting on a pile's shaft subjected to these conditions.