Model Studies on Load Sharing for Shaft and Tip of Pile Groups in Saturated and Unsaturated Soils

The behavior of pile foundation is dictated by its structural properties and stiffness and strength of the soil supporting the pile. This complexity is further increased when the soil is in partially saturated condition. In this work, an attempt has been done to investigate the influence of matric suction on the behavior of single pile and pile group, and the amount of increase in the bearing capacity due to the influence of this suction. The load transfer for shaft and tip of pile groups embedded in soil with different properties (saturated and unsaturated) is investigated. First, the stresses below the center of piles are measured by a soil pressure transducer located at a depth of 0.25 L, (L = length of pile). These stresses are transferred directly to pile tip according to approximate 2 V:1 H method and then converted to load at the tip and shaft of pile. The general trend is that in a single pile, at the start of load applying, the percentage of distributed load is 70% for shaft and 30% for tip, then as the applied load increases, the pile settles and a differential movement between the soil and pile occurs, creating more adhesion between the soil resulting in increase in shaft capacity. For pile groups, the same trend is obtained, but the percentage of load transferred to the shaft increases as the number of piles increases, in contrast to the load transferred to the tip. The results showed that the sharing of load between shaft and end resistance for single pile in saturated soil is halved when the pile reaches its ultimate resistance, while this response is different for unsaturated soil where the load is transferred as a whole to the pile tip at approximately the intermediate stages of loading according to the analysis criteria adopted.