Numerical study of dynamic stress developed in the high speed rail foundation under train loads

As a ground treatment method, geosynthetic-reinforced pile foundation (GRPF) is widely applied in the railway construction, especially in high-speed railway (HSR), due to the strict restrictions on post-construction settlement. The post-construction settlement is commonly considered induced by the weight of railway structure as well as the moving train load. Therefore, the dynamic stress developed in the GRPF induced by HSR is important for the post-construction settlement study. However, most studies focus on the dynamic stress on the track and subgrade, studies concerning dynamic stress in GRPF are few. In this paper, a three-dimensional time-domain viscoelastic finite element method (FEM) model is developed to study the dynamic response of GRPF under the high-speed rail load. The simulation model is verified by a comparison with the results of analytical solution. And based on this model, parameter study is conducted. The investigation of train speed and the pile group layout has shown that the dynamic stress amplitude significantly increases after the train speed reaches the Rayleigh wave velocity of the subgrade, while the pile-soil stress acts reversely. For the influence of the pile group layout, three variables: pile cap size, longitudinal pile spacing, and lateral pile spacing are studied respectively. A parametric study of pile cap size, longitudinal pile spacing and lateral pile spacing have suggested that the amplitude of dynamic stress developed in the soil is more susceptible to the pile spacing rather than pile cap size. Besides, increasing replacement ratio results in the decrease of dynamic pile-soil stress ratio.