Cap-Stiffness on Behaviour of Rigid Passive Piles

This paper develops a new 3-layer model and its solutions. The solutions are subsequently used to examine the mobilization law of limiting force per unit length p(1) with the cap-rotation stiffness, sliding depth, and axial load level and nonlinear response of rigid passive piles against model pile tests. The study indicates the parameters for single pile can generally be used for 2-pile groups, but for using a group interaction factor pm for modulus and limiting p(l), etc. The pm is found to be 0.5-0.6 for a sliding depth (SD) of similar to 30% pile length (l), which increases towards unity as the depth exceeds 0.5l. This is associated with transition towards rotation of pile groups. The limiting pl reduces by a displacement ratio alpha (soil movement over pile displacement owing to loading distance at similar to 0.5l) of 1.67 similar to 3.0 (SD = 0.29l), and 1 (SD = 0.5l). It drops to similar to 25% that on free-head piles (resembling the load ratio of laterally loaded piles). The study is the first of its kind on detecting impact of rotational-stiffness, axial loading, and group interaction on passive piles, which should be useful to the pile design.