A series of large-scale shaking table tests were carried out to investigate the seismic performance of different cement-soil reinforced pile groups in liquefiable sands. Specifically, sinewave scanning was performed on three cement-soil reinforced 3 x 3 pile groups and one conventional (unimproved) 3 x 3 pile group. In this study, the bending moment of group piles, the horizontal displacement of the superstructure, pore water pressure into soils, and the settlement and acceleration response of piles and the ground under different earthquake intensities were recorded. The natural frequency of the ground and the dynamic stress-strain relationship of the soils around piles were obtained. The results show that the acceleration response of the improved pile groups before soil liquefaction is significantly smaller than that of the unimproved pile group. However, the acceleration attenuation of the unimproved pile groups after soil liquefaction is substantially greater than that of the improved pile group. In addition, the lateral displacement of the superstructure, the settlement of pile heads, the bending moment of pile shafts, and the dynamic shear strain of the soils around piles in improved cases are all smaller than those in the unimproved case. In particular, the improved cases significantly suppressed the pile bending moment at the interface between the liquefied layer and the non-liquefied layer. The spatial layout of cement-soils significantly impacts the natural frequency and stress changes of the pile-soil Winkel elastic foundation beam systems.

Coupled nonlinear thermo-hydro-mechanical finite element simulations were carried out to investigate the behavior of energy micropiles subjected to thermal loading cycles. Two kinds of problems were analyzed: The case of an isolated micropile, for which comparison with previous research on medium-size isolated energy pile is provided, and the case of large groups of micropiles, with the aim of investigating the interaction effects. In both problems, micropiles were considered installed in a thick layer of very soft, saturated clay, characterized by isotropic or anisotropic hydraulic conductivity. Two advanced existing hypoplastic models, one incorporating the thermal softening feature, were used to describe the clay behavior in both problems. The settlements of the micropile head were found to increase during thermal cycles under constant mechanical load, showing a sort of ratcheting. For micropile groups, the settlement increase rate was faster as the spacing between micropiles was reduced. The excess pore water pressures developed at the micropile-soil interface played a significant role on the deformation and displacement fields of the soil-micropile systems, especially in the case of micropile groups, affecting the shear strength developed at the micropile-soil interface. The consolidation process was faster when the hydraulic conductivity was anisotropic, meaning that the development of excess pore water pressure was reduced in this case. As the spacing between the micropiles increased, i.e., as thermal interaction decreased, the heat flux exchanged by a micropile of the group during one cycle approached the heat flux exchanged by an isolated micropile in the same period.

The aim of this paper is to propose a two-stage theory-based analytical method for the dynamic performance of pile groups in layered poroelastic saturated cross-anisotropic soils induced by moving loadings. Among them, the free-field vibrational analysis of saturated soils is performed by the analytical element-layer approach (ALEA) and Fourier transformation. Based on the free-field response, the boundary element (BE) solution for the soil resistance at the soil-pile interface is derived utilizing the two-stage theory. Simultaneously, the finite element (FE) solutions for the pile shaft resistance and deformation of pile groups are derived based on the Timoshenko beam theory. Finally, the FE-BE coupled dynamic equation for deformations and internal loadings of the soil-pile system is obtained. Thereafter, the reliability of the proposed method is validated by comparing with existing solutions and FE data from ABAQUS. Based on the derived solutions, a comprehensive parametric study is performed to examine the effects of loading amplitude, force speed, soft soil-layer stiffness, soil anisotropy, and pile length on the dynamic responses of pile groups.

The mechanical response of energy pile groups in layered cross-anisotropic soils under vertical loadings is studied with the aid of the coupled finite element method- boundary element method (FEM-BEM). The single energy pile is simulated based on the finite element theory, which then is extended to energy pile groups. The global flexibility matrix for soils is obtained by considering the coupling effects of vertical and thermal loadings. The coupled FEM-BEM equation for the interaction between energy pile groups and soils is derived based on the displacement compatibility condition at the pile-soil interface. According to the displacement coordination condition and force balance in the rigid cap, the displacement of the cap and axial forces of pile groups can be solved. The presented theory is validated by comparing the calculated results with numerical simulations and field test results in existing literature. Finally, effects of the thermal loading, pile-soil stiffness ratio, pile spacing, cross-anisotropy of Young's modulus and the stratification are discussed.

The pile foundations are frequently affected by adjacent traffic loads except for general active loads. However, the dynamic responses of the pile groups under moving loads have been rarely reported before. In addition, the influence of material anisotropy is often neglected. In this paper, a three-dimensional (3D) analytical model for the dynamic analysis of partially buried pile groups in stratified saturated cross-anisotropic media under adjacent moving harmonic loadings is developed. Specifically, a 3D Bernoulli-Euler beam theory is adopted to simulate the monopile and then superimposed into the finite element (FE) formulation for the partially embedded pile groups. Subsequently, the basic solutions of layered saturated cross-anisotropic soils are derived by the analytical layer-element approach (ALEA). By combination with ALEA, the two-stage based boundary element (BE) equations for the pile-soil interface are obtained. Finally, by coupling the FE and BE formulations, the dynamical response equation of pile-soil is established. Based on the verification of the accuracy of the proposed methodology by comparisons with existing solutions and FE results from ABAQUS, the impacts of material anisotropy, pile buried length, loading velocity, and pile stiffness on the time-domain dynamic behavior of pile groups are analyzed. The results show that increasing the pile-buried ratio or pile stiffness reduces the magnitude of the dynamic response. Moreover, with the increase of material anisotropic parameters, the peak pile response decreases. And the peak dynamic response first increases and then reduces as the loading velocity increases.