Design method and experimental study of uplift bearing capacity of the lower enlarged composite pile

The lower enlarged composite pile is a newly developed uplift pile. The uplift mechanism of the lower enlarged composite pile is analyzed by combining theoretical analysis and field experiments. Based on this, the theoretical model and calculation parameters of uplift bearing capacity of the single pile for this pile type are proposed. The results show that the lateral resistance of the lower enlarged pile is enhanced by the effect of the upper resistance under a certain thickness of overlying soil layer. The mobilization factor can be 1.6 when calculated by empirical parameter method under testing conditions. The uplift bearing capacity of the upper non-enlarged composite pile is weakened by the influence of the upper resistance of the enlarged section, and the mobilization is decreased. When the pile diameter of the upper non-enlarged section is smaller than that of the enlarged section, the uplift bearing capacity of the lower enlarged composite pile is calculated by considering only the lateral resistance of the enlarged section and the upper resistance. The reliability and practicability of the model and theoretical method are verified through comparison with experimental results. The research results can be used as a reference for engineering design.