Model tests on the lateral cyclic responses of a caisson-piles foundation under scour

As a new type of deep foundation, the caisson-piles composite foundation is a selection for the Qiongzhou Straits bridges. It can greatly reduce the height of the caisson by connecting the lower pile groups to the upper caisson, and improves its mechanical behaviour under lateral load. Aseries of model tests are conducted at 1g to investigate the scour effects on the responses of the caisson-piles composite foundation under long-term lateral cyclic load, in which two scour depths and two cyclic load amplitudes are applied. The cyclic load pattern is single cycle sinusoidal curve with 10,000 cycles. Based on the test results, the accumulated residual rotations are found to be dependent on the scour depth and the applied cyclic load amplitude. An empirical method is developed to predict the accumulated rotation due to long-term cyclic loading, in which the effect of scour is considered by a revised dimensionless cyclic load level, relating the cyclic load magnitude to the post-scour lateral capacity of the composite foundation.