Vertical bearing behavior and pile group effect for cemented-soil composite pile groups based on on-site experiments

Bearing characteristics and interactions of a pile group are complex. and there is almost no on-site full-scale test data for cemented-soil composite pile group. In this research, vertical static load tests were conducted on two isolated pile, two-pile group and six-pile group for long-core SDCM pile. The bearing behavior of long-core SDCM pile and the interaction between pile groups have been studied. The results indicate that the long-core SDCM single pile is a typical friction type pile, and cemented soil provides most of the lateral friction resistance for the bearing capacity. In pile groups, pile spacing is the main factor affecting the pile group effect. The model calculation results based on the equivalent pier method are verified using on-site test data and the key parameters in the pile group for long-core SDCM pile including pile spacing S_ij, cemented soil Elastic modulus E_c and PHC pipe pile Elastic modulus E_p are analyzed using a mathematical model. Parameter analysis results indicate that the pile group interaction for long-core SDCM pile is mainly reflected in settlement. Group effect is inapparent at pile spacing greater than 4 D. The appropriate value of E_c and E_p are taken in the range of 1.2–1.6 GPa and 30–40 GPa.