Axial load transfer in liquefiable soils for free-standing piles

The shaft friction capacity of a piled foundation is commonly linked to the effective stresses acting on the pile, and hence it is assumed that if the surrounding soil liquefies following an earthquake event, the shaft friction capacity of a pile drops to zero. In this paper an investigation into the axial load transfer during a liquefaction event based on dynamic centrifuge test results is presented. A free-standing pile group with the pile cap clear of the ground surface is considered, to clarify the mechanism of load transfer. The pile group was instrumented to measure axial loading at several locations along the pile length, and was embedded in a saturated soil profile where a dense permeable base layer was overlain by a layer of loose, liquefiable sand. The results show that shaft friction continues to be maintained during an earthquake in both loose and dense soil. In the case of loose soils, the apparent shaft friction capacity is proposed with reference to the shear taking place at the pile/soil interface, which causes a local reduction in the pore pressures.