Investigation of cyclic pile-sand interface weakening mechanism based on large-scale CNS cyclic direct shear tests

Abstract

Bearing capacity failures of offshore pile foundations under cyclic loads in sandy soils are usually initiated by soil strength reduction due to cyclic pile-sand interface sliding. In this paper, a large-scale constant normal stiffness (CNS) cyclic direct shear apparatus is designed to simulate this sliding mechanism, with an effective shearing area of 0.14 m2. The cyclic pile-sand interface behaviour of two common types of piles (concrete and steel piles) is subsequently investigated under different confining pressures and cyclic deformation amplitudes. The experimentally obtained results, including the induced shear/normal stress-displacement behaviour, stress path behaviour and particle distribution at the pile-sand interface, are analysed. This further leads to a detailed study for the associated pile-sand interface cyclic weakening mechanism, through the investigations of cyclic attenuation of shear/normal stress amplitude, strength reduction and particle crushing, respectively. Furthermore, experimental results highlight the effect of initial confining pressure, cyclic shear deformation amplitude and pile surface roughness on the investigated pile-sand interface cyclic weakening mechanism.