Characteristic study of horizontal bearing capacity and pile group effect coefficient of laterally loaded high pile group foundation for bridge in soft soil

Pile group foundations with high cap, as a common form of high-speed railway bridge foundation, are generally subjected to lateral loading due to wind action, earthquake, etc. In this paper, indoor physical model tests and three-dimensional finite element analyses using ABAQUS are both conducted to study the bearing capacity of laterally loaded single pile and pile foundation in soft soil layer. Soft soil is modelled by the modified Cam clay constitutive model in 3D FEM. The test results and finite element calculation results are in good agreement. The research of group pile are carried out by varying the piles number and pile spacing. The results show that the average lateral bearing capacity of pile foundation(total capacity divided by number of piles) is substantially higher than that of the single pile; and it also increases with the increase of the pile spacing in the direction of laterally load. Threedimensional spatial effect is found in laterally loaded pile group foundation. The magnitude of internal force in pile varies with its spatial location. The corner pile has the maximum force, then the side pile, and the minimum force is found in the middle pile. The difference between the maximum and minimum bending moments is up to 20%. The range of surrounding soil influenced by pile group foundation is about 16 times pile diameter from the peripheral edge of the pile foundation. The pile and pile interaction effect of pile group is disadvantageous to its laterally loading capacity; and the cap constraint effect is favourable for the bearing capacity. The computing method for the effect coefficient of pile group is presented. The calculation results show that the presented computing method can be applied to the design of high cap pile group foundation in soft soil area in terms of laterally loading capacity.