This study considers the saturated soil around the tunnel as a transversely isotropic medium and derives the dynamic response solutions of the tunnel lining and its surrounding medium under explosive loads in the Laplace and Fourier transform domains. When the transverse isotropic coefficient equals 1.0, this solution simplifies to the case where the tunnel is surrounded by a uniform medium. By performing inverse Fourier and Laplace transforms on the solution, we obtain the time domain solution. Compared with the results for a uniform medium surrounding the tunnel, it was found that the peak values of stress and pore water pressure increased, while the peak displacement slightly decreased. In addition, the peak arrival time is advanced, and the fluctuation attenuation is accelerated. The transverse isotropy of soil in engineering cannot be ignored.

BackgroundThe dynamic coupled hydro-thermo-mechanical behavior of the unlined structure in saturated porous structure under extreme geotechnical and geology engineering (e.g., underground explosion, laser thermal rock breaking) have aroused extensive research interests on the constitutive modeling and transient dynamic responses prediction. Although the current fractional-order hydro-thermo-mechanical models have been historically proposed, the theoretical formulations still adopt the classical fractional derivatives with singular kernels, and the inherent strain relaxation effect and the associated memory dependency remains not considered yet in such complex condition.PurposeTo compensate for such deficiencies, the current work aims to establish the new hydro-thermo-mechanical model by introducing the Atangana-Baleanu (AB) and Tempered-Caputo (TC) fractional derivatives with non-singular kernels.MethodsThe proposed model is applied to investigate transient structural dynamic hydro-thermo-mechanical response of a cylindrical unlined tunnel in poroelastic medium by applying Laplace transformation approach.ResultsThe influences of the AB and TC fractional derivatives on the wave propagations as well as the dimensionless responses of the temperature, displacement, stress, and pore-water pressure are evaluated and discussed.ConclusionThe non-singular AB and TC fractional derivatives slower the thermal wave propagation. In addition, the dimensionless pore water pressure dissipation is maximally reduced. The increase of strain relaxation time parameter reduces the mechanical dynamic response regions and eliminates the sharp jumps of mechanical response at the elastic wave front, which are consistent with continuity of displacement in real engineering situations.

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.