Centrifuge model tests for distinguishing kinematic and inertial loads on single piles in liquefiable sloping ground

Existing design guidelines for considering the kinematic and inertial effects on piles and their combination in seismic design of piles in liquefaction-induced lateral spreading ground provide conflicting recommendations, partly because experimental data on the phase relationship between the kinematic load and the inertial load on piles is limited. In this study, a centrifuge shaking table test was conducted on single piles embedded in a half sloping liquefiable ground. Two single piles with and without superstructure mass at pile heads were used to represent pile foundations with different loading combinations. The pile with a superstructure was used to simulate the seismic response under the combined effects of kinematic and inertial loads, while the pile without a superstructure simulated the response dominated by kinematic loads. The soil model consisted of a clay crust overlying a saturated loose sand layer, which was underlain by a saturated dense sand layer. The results showed that the depth of the maximum bending moment of the pile with a superstructure was shallower than that of the pile without a superstructure. The bending moment response of piles may be predominantly governed by inertial loads, even when the kinematic load was substantial. For the pile with a superstructure, the kinematic and inertial loads were out-of-phase, whereas for the pile without a superstructure with negligible inertial effect, the two loads were in-phase. The kinematic and inertial loads were out-of-phase when the natural period of pile was greater than that of the ground; otherwise, the two loads acted in-phase.