To investigate the three-dimensional dynamic response of a deeply buried storage and drainage tunnel in saturated soil subjected to water hammer, we propose a frequency-domain finite element method and boundary element method (FEM-BEM) coupling model for the fluid-lining-saturated soil system. The fluid is modeled as an inviscid and compressible fluid, the lining as an elastic medium conceptualized as a hollow cylinder of finite length, and the soil as a saturated poroelastic medium. Initially, the governing equations for the fluid and lining are solved using FEM in the frequency domain, while those for the soil are solved using BEM in the same domain. In the following, fluid, lining, and soil are coupled based on the conditions of deformation compatibility, force equilibrium, and impermeable boundary conditions at their interfaces. The presented model is verified through the comparison with the existing models. Finally, a case study of internal water pressure (water-hammer load) and the displacement and pore pressure of the saturated soil in a fluid-filled lined tunnel due to water hammer is presented. The results show that: (1) The dynamic response caused by the water hammer presents significant periodicity and attenuation. (2) The radial displacement of soil is significantly larger than that of axial displacement. (3) Modeling soil as a single-phase elastic medium inaccurately evaluates the dynamic response. (4) The water hammer makes an extensive impact on the ground surrounding the storage and drainage tunnel. (5) The peak values of internal fluid pressure, the soil displacement and pore pressure decrease with the decrease of soil permeability.

This paper studies the time-dependent behavior of a pile drilled in layered saturated viscoelastic rock-soil mass due to a vertical load. By virtue of the finite element method (FEM), the pile is discretized into three-node axial bar elements. On the basis of the consolidation solution of layered transversely isotropic saturated rock-soil mass, the fractional Poyting-Thomson model and fractional Merchant model are used to simulate the rheological properties of rock and soil, respectively. The viscoelastic solution of layered saturated rock-soil mass under annular linear loads is derived according to the elastic-viscoelastic correspondence principle. Taking the above solutions as the kernel functions of the boundary element method (BEM), and combining with the stiffness matrix equation of a pile, a coupling formula of pile-soil-rock interaction is further established by the FEM-BEM coupling method. A MATLAB code is developed for numerical calculation, and the correctness of the present theory and calculation method are verified by comparing with the existing solutions, field tests and ABAQUS analyses. Finally, the key factors influencing the time-dependent behavior of piles are in-depth discussed.

This study investigates the interaction between energy piles and layered saturated soils, considering the consolidation induced by the thermal loads and mechanical loads. Initially, the coupled thermo-hydromechanical solution of layered media is obtained by utilizing the boundary element method (BEM) and the transformed differential quadrature method. Subsequently, the energy piles are discretized and modelled by the finite element method (FEM), and the solving equation for piles is established. To reflect the interaction between piles and soils, a coupled BEM-FEM matrix equation is formulated and solved by incorporating displacement coordination conditions and force equilibrium conditions. This approach facilitates the analysis of the temporal evolution of displacements and temperatures of piles and surrounding soils. The proposed methodology is validated through comparisons with monitoring data of field tests and results from simulations. Ultimately, the key factors, including the temperature increments, mechanical loads, length-diameter aspect ratio are examined through examples.

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.

Dynamic stress responses of saturated soil around a fluid-filled lined tunnel caused by a water hammer are investigated by a frequency-domain FEM-BEM coupled model. The fluid is modeled as an inviscid and compressible fluid, the lining is modeled by elastic medium and conceptualized as a hollow cylinder of finite length, and the saturated poroelastic medium is adopted to model the soil. Initially, governing equations of fluid and those of lining are solved by FEM in the frequency domain, while those of soil are solved by BEM in the same domain. In the following, fluid, lining, and soil are coupled based on the conditions of deformation compatibility and force balance on their interfaces. Water pressure (inside the tunnel), the distribution of lining displacement and dynamic stress responses of saturated soil generated by the water hammer are presented. It is concluded that the dynamic stresses and the pore pressure change periodically in saturated soil under a water hammer. Modeling soil as an elastic medium inaccurately evaluates the distribution of lining displacement. The soil permeability has a significant influence on the normal stresses of soil and pore pressure but has a slight effect on the shear stresses of soil.