软土地层高承台桥梁群桩基础横向承载特性研究

高承台群桩基础是高速铁路桥梁基础的一种常用形式，受到风、地震等荷载作用影响，常常需要承受较大的横向荷载。采用室内物理模型试验和三维有限元程序ABAQUS对软土地层中单桩、群桩的横向承载特性进行了研究，软土采用修正剑桥黏土本构模型，试验结果与有限元计算结果吻合较好。群桩研究方案包括了桩数的变化以及桩间距的变化。结果表明，群桩基础的基桩平均横向承载力（总承载力/桩数）较单桩基础显著增加，且水平荷载方向桩间距越大，其横向承载力越大；群桩基础基桩受力存在三维空间效应，不同位置基桩受力大小排序为角桩最大，其次为边桩，最小为中间桩，弯矩极值差异可达20%，群桩基础桩周土影响范围距外围基桩边缘净距离约为16D (D为桩径)。桩与桩相互影响效应对群桩水平承载不利，承台约束效应对水平承载有利。探讨了考虑上述两种效应的群桩效应系数计算方法，通过计算验证了该方法在软土地区高承台群桩基础横向承载力计算中的适用性。

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. Three- dimensional 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.