Responses of caisson-piles foundations to long-term cyclic lateral load and scouring

Abstract

The caisson-piles composite foundation is considered as a viable alternative to caisson foundations for the Qiongzhou Strait bridge. It can significantly reduce the caisson height by connecting the lower grouped piles to the upper caisson and improve its mechanical behaviour under lateral loading. A series of model tests are conducted at 1 g to investigate the cyclic responses as well as the coupled cyclic and scouring responses of the caisson-piles composite foundation under 10,000 cycles. The cyclic responses of the caisson-4 piles composite foundation are compared with those of a conventional caisson, including various cyclic load characteristics, i.e., one-way, asymmetric two-way and symmetric two-way cyclic loading. Two scour depths and two cyclic load amplitudes for the one-way cyclic loading are applied in the coupled tests. A framework to predict the accumulated deformation of the caisson-piles composite foundation due to cyclic loading and scouring is developed. It is found that the accumulated residual displacements or rotations are dependent on the applied cyclic load characteristic and scour depth, and the most onerous loading condition is between one-way and symmetric two-way loading. The effect of scouring can be rationally assessed using a modified cyclic load level, replacing the static capacity by the post-scour static capacity.