Cyclic p-y curves for lattice-shaped diaphragm walls considering softening behavior of marine clays

Lattice-shaped diaphragm walls (LSDWs) are increasingly used as high bearing capacity foundations for the main towers and anchorage structures of cross-sea bridges in soft marine deposits, yet a dedicated p-y framework for their horizontal cyclic response in cohesive soils remains unavailable. This study establishes the first cyclic p-y framework for single-cell LSDWs by extending the established static LSDW p-y model to account for the cyclic degradation effect of soft clay under repeated lateral loading. A cyclic degradation model for cohesive soils is first adopted, and its applicability is verified by field data. Three-dimensional numerical analyses of single-cell LSDWs are then performed to extract representative cyclic p-y curves, from which the evolution of ultimate soil resistance and stiffness-related parameters is quantified with respect to the number of load cycles and the cyclic load amplitude. Based on these results, modification functions are proposed while preserving the original form of the static p-y relationship. Validation using a full-scale field loading case shows consistent agreement with field-derived p-y responses, and comparisons indicate that API clay p-y curves tend to underestimate soil resistance under cyclic loading. A simplified design procedure is finally presented to facilitate practical application of the proposed cyclic p-y framework.