A method for calculating composite foundation bearing capacity by results of load tests on piles and soils

In the technical code, the bearing capacity characteristic value of composite foundation is the sum of bearing capacity characteristic values of piles and soils adjusted by empirical coefficients, which is called the characteristic value design method. Due to the difficulty of determing the empirical coefficients, it is not easy to obtain the accurate results. The bearing capacities of the piles and the soils are based on the load tests. In the load tests, the bearing capacity characteristic values of the composite foundation and soils are directly confirmed by the relative deformation value, but the bearing capacity characteristic value of pile is indirectly confirmed by the absolute deformation value that first determines the ultimate bearing capacity of single pile and then the characteristic value. The above methods and indexes are not matched, and it is a significant reason leading to the inaccurate calculated results by means of the characteristic value design method. In the limit state design method, when the piles reach the limit state, the soil state is regarded as the limit state. The ultimate bearing capacity of the composite foundation is the sum of the ultimate bearing capacity of the piles and the assumed ultimate bearing capacity of the soils, and the characteristic value takes half. This method needs less empirical coefficients, and it is practical, more correctness and safety when the conditions are enough.