Response of rigid piles during passive dragging

This paper develops a three-layer model and elastic solutions to capture nonlinear response of rigid, passive piles in sliding soil. Elastic solutions are obtained for an equivalent force per unit length ps of the soil movement. They are repeated for a series of linearly increasing ps (with depth) to yield the nonlinear response. The parameters underpinning the model are determined against pertinent numerical solutions and model tests on passive free-head and capped piles. The solutions are presented in non-dimensional charts and elaborated through three examples. The study reveals the following: On-pile pressure in rotationally restrained, sliding layer reduces by a factor α, which resembles the p-multiplier for a laterally loaded, capped pile, but for its increase with vertical loading (embankment surcharge), and stiffness of underlying stiff layer: α=0.25 and 0.6 for a shallow, translating and rotating piles, respectively; α=0.33-0.5 and 0.8-1.3 for a slide overlying a stiff layer concerning a uniform and a linearly increasing pressure, respectively; and α=0.5-0.72 for moving clay under embankment loading. Ultimate state is well defined using the ratio of passive earth pressure coefficient over that of active earth pressure. The subgrade modulus for a large soil movement may be scaled from model tests. The normalised rotational stiffness is equal to 0.1-0.15 for the capped piles, which increases the pile displacement with depth. The three-layer model solutions well predict nonlinear response of capped piles subjected to passive loading, which may be used for pertinent design.