Abstract: 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.

Key words: water hammer, storage and drainage tunnel, finite element method and boundary element method (FEM-BEM), saturated soil, dynamic response