Pile-Group Response to Large Soil Displacements and Liquefaction: Centrifuge Experiments versus a Physically Simplified Analysis

The paper presents a physically simplified method for computing displacements and structural forces on piles under conditions of lateral spreading triggered by the large seaward displacement of a harbor quay wall. The method avoids the empirical selection of stiffness-reduction factors and the associated use of $p\text{-}y$ curves that current state-of-the-art methods use. Instead, the three-dimensional (3D) highly nonlinear problem is approximated in two steps, both involving two-dimensional (2D) plane-strain analyses. The first step involves a vertical (representative) slice in which the pile group has been omitted and that, shaken at its base, gives the permanent deformation of the quay wall and of the liquefiable soil. It is an effective stress analysis. In the second step, a horizontal (representative) slice taken from the middle of the liquefiable zone is subjected to an outward quay wall displacement; the goal is to evaluate the reduction of the pile displacement over the free-field one and the ensuing pile group distress. The pile resistance to ground deformation depends heavily on the constraints imposed by the superstructure, as well on the exact stiffness of the soil layers. Thus, the interplay between soil piles-quay wall under soil flow conditions is captured in a physically meaningful way. The predictions compare well with results from two centrifuge tests.