Abstract：By comparing the mechanical properties of pier foundation with those of normal non-reinforced spread foundation and cast-in-situ pile with hand excavation，the working mechanism，ground failure mode，and bearing capacity about pier foundation combined with flat and wide grade beams are analyzed. The influence of soil groups of sustaining layer，bottom diameter of pier foundation，relative embedment depth and soil compactness on the increase coefficients of subgrade bearing capacity in pier foundation are discussed. Then，the conclusion in which the bearing capacity of pier foundation is higher than that of cast-in-situ pile with hand excavation is achieved，and the empirical formulas for increase coefficients of subgrade bearing capacity in pier foundation and cast-in-situ pile with hand excavation are presented. It is also found that designing cast-in-situ pile with hand excavation with the smaller relative embedment depth according to the code，which is being used，will lead to a relatively larger calculation result. This will be danger in engineering application.
