Soil arching effect of composite piles supporting foundation pits based on mechanical model and photoelastic experiment

•After the composite pile supporting the foundation pit, an analytical solution of soil stress is presented, and its correctness is verified.•An effective annealing process for removing residual stress of polycarbonate plate was proposed.•Photoelastic experiments determine the soil arch area of the composite pile supporting the foundation pit.•The functional relationship between arch height, pile diameter, pile spacing, and load is established.