Dynamic response of unsaturated full-space caused by a circular tunnel subjected to a vertical harmonic point load

Abstract

This study proposes a model to analyze a deep tunnel embedded in unsaturated soil. Key feature is the consideration of the coupled soil water and air. The analysis emphasizes on the dynamic responses of wave field induced by a unit vertical harmonic point load on the invert level of tunnel. The tunnel is modelled as an infinitely long shell with a circular section. The soil is simulated as an unsaturated poroelastic full-space in which the solid matrix is filled with the coupled soil water and air. Stress compatibility and displacement continuity are used to describe the interaction between the tunnel and the soil. A good agreement regarding the results of soil displacements between the present model and existing models for saturated soil and elastic media confirms the validity of the proposed model. The numerical analysis investigates the effects of water saturation on soil displacements and matric suction under different load frequencies. The results reveal that the dynamic responses of unsaturated soil are different from those in saturated soil. Increased water saturation can vary the value of displacements and matric suction of the soil, but not their distribution pattern around the tunnel. Displacements and matric suction distribution curves along the circumferences of the tunnel have more peak points in the case of higher load frequencies.