Behaviors and group effects of pile composite foundation under lateral load

Pile composite foundation (PCF) supporting anchorage foundations and immersed tube foundations is subjected to significant vertical and lateral loads, where the PCF design is often controlled by the lateral displacement of PCF head. Therefore, the behavior of lateral loaded PCF is an important issue concerned by engineers, but no published design guidance can be referred. An semi-analytical method is adopted to predict the lateral loaded PCF behaviors, where the reduction factor of the t-th row fp(t) and group efficiency factor fg are induced to account for the group effects. The PCF system is decomposed into fictitious piles and extended soil, and fictitious piles are treated as Bernoulli-Euler beam. The governing equation is formulated based on the compatibility condition of lateral displacement between extended soil and fictitious piles and solved by numerical solution. The analytical results are validated against public theoretical solutions and FEM solutions, and provide very satisfactory results. The PCF behaviors, reduction factor per row fp(t) and group efficiency factor fg are widely investigated by considering some primary influence factors, such as the ratio of pile length to diameter l/d, the ratio of pile spacing to diameter s/d, the number of piles N and the layout form. It is shown that: (1) the surface load on soil elements between piles take a noticeable influence on the deflection and moment distribution along pile shaft; (2) the lateral stiffness of the i-th pile ki, fp(t), fg decrease with increasing s/d, and the l/d has a negligible effect on the fp(t) and fg; (3) the fg of in-line layout is larger than the fg of square array layout and smaller than side-by-side layout form, and fg decrease with the increasing the number of piles N in PCF regardless of pile layout form. The research is expected to provide insights to the practitioners on the lateral loaded PCF design.