Pile response to liquefaction-induced lateral spread

This work deals with the response of pile foundations to ground displacements caused by soil liquefaction. Methods are developed to estimate failure modes of single piles to liquefaction-induced lateral spread and assess maximum levels of soil displacement to cause pile failure.;A finite element model is developed to study the response of single piles and pile groups to horizontal ground displacements caused by soil liquefaction. The analytical model is implemented in a computer program called B-STRUCT. The program is evaluated by validation against benchmark problems and by comparing numerical predictions with observed pile foundation damage resulting from lateral spread during earthquakes.;Three failure mechanisms, excessive bending, buckling, and soil flow are recognized under lateral spread conditions. Each is a function of the relative stiffness between soil and pile, and the axial load carried by the pile. At high relative stiffness piles may fail by excessive bending. With decreasing relative stiffness, a soil flow condition may develop in which the liquefied soil flows around the pile without inducing additional pile deflections. This mode of pile response is considered safe and provides the basis for acceptable design against structural failure.;Buckling may develop as a result of lateral pile displacement and reduced soil stiffness. As the relative stiffness of soil to pile increases, the buckling load increases and the failure mode of the pile becomes one of excessive bending. Analytical results are combined to develop dimensionless plots which allow for the determination of failure mechanisms on the basis of relative stiffness and applied axial load. For the first time, these results show quantitatively how the behavior of deep foundations changes as the ground alters its force-displacement characteristics from a soil-like to a fluid-like medium. Dimensionless plots also are developed to determine surface soil displacement required to induce the formation of a plastic hinge under excessive bending conditions.;A simplified model for pile groups is developed which accounts for the stiffness of the soil within the pile group. The stiffness of the enclosed soil plays an important role in pile group behavior under lateral spread. As the stiffness of the enclosed soil increases, the failure mode changes from excessive bending to a soil flow condition. A simplified procedure is proposed for estimating group displacement as a function of relative stiffness between the soil mass and the pile group.