Jonathan Knappett

Effects of Axial Load and Slope Arrangement on Pile Group Response in Laterally Spreading Soils

AbstractThis paper presents the results of a series of dynamic centrifuge tests that were conducted for 2×2 pile groups in a three-layer laterally spreading soil profile consisting of a nonliquefiable cohesive crust overlying loose, liquefiable sand, overlying dense sand. Two main variables are considered, both of which received little attention in previous work on piles in laterally spreading soils, namely (1)xa0the axial load carried by the foundation, and (2)xa0whether the slope boundary conditions are infinite or finite. The data show that the presence of axial load reduces the lateral stiffness of the foundation resulting from P-Δ effects and reduces their capacity to resist lateral kinematic loads from spreading soil. This degradation in lateral response (bending) may be accompanied by substantial settlement of the foundation as a competing failure mode that must also be considered in design. Furthermore, the mechanical response of the liquefied soil appears to vary greatly with the slope boundary condi...

Mechanism of pile group settlement in liquefiable soils

This paper examines the settlement of instrumented 2 · 2 model pile groups in liquefiable soil based on the results of dynamic centrifuge tests. The piles are end-bearing in dense sand, and are instrumented such that base, shaft and total pile load components can be measured. The data suggest that the overall co-seismic group settlement is accrued from incremental settlements of the individual piles as the group rocks under the action of the kinematic and inertial lateral loads. A Newmarkian framework for describing this behaviour is presented in which permanent settlement is incremented whenever the load in any of the piles exceeds the capacity of the soil to support the pile. This bearing capacity of the piles in liquefied soil is estimated based on measured dynamic soil properties during shaking and observations of the changes in load carried by the piles. The contribution of the pile cap in reducing settlement is also discussed.