The Horizontal Bearing Characteristics of a Rigid Long–Short Pile Composite Foundation under Combined Vertical and Horizontal Loads

A lack of research exists on the mechanical response of rigid long–short–pile composite foundations (LSPCFs) under combined vertical and horizontal loads. A large-scale indoor model test is conducted in this study to evaluate the resistance of piles with different lengths to horizontal loads. A three-dimensional coupled-continuum model is established. The mechanical properties of the LSPCF, such as the stress, strain, and displacement fields and the force chain, are discussed. The results show that the raft, cushion, and pile resist the horizontal force. The vertical stress on the pile top reduces the pile’s horizontal displacement and bending moment caused by the horizontal loads, improving the horizontal bearing capacity of the composite foundation. The magnitude of the horizontal displacement of the pile and the horizontal load borne by the pile are related to the piles’ positions. The horizontal load causes an uneven settlement of the composite foundation, and the horizontal load-sharing ratio significantly differs for piles at different positions. The front-row piles bear a higher horizontal load than the back-row piles, and the long piles bear a higher horizontal load than the short piles. For piles of equal length, the horizontal displacement of the front row is approximately 1.5 times that of the back row. This study research provides some new insights into the interaction between LSPCFs and surrounding soil under combined vertical and horizontal loads.