Scattering of Plane SV Waves by an Underground Tunnel in an Unsaturated Soil Half-Space

Based on unsaturated poroelastic media theory, this study establishes an analytical model for the scattering of plane SV waves by an underground tunnel in an unsaturated half-space using the Fourier-Bessel series expansion of wave functions. Numerical analyses are performed to investigate the effects of saturation, incident frequency, incident angle, and burial depth ratio on surface displacement and the dynamic stress concentration factor (DSCF) around the tunnel. The results show that saturation and incident frequency exhibit a pronounced coupling effect. Surface displacement and DSCF exhibit asynchronous evolution under different parameter combinations. The incident angle significantly modulates the spatial distribution of the wave field. Near the critical angle, the coupled interaction between the incident SV wave and the converted P wave, together with multi-wave interference, is markedly enhanced. Increasing burial depth attenuates the surface response, whereas its effect on the tunnel DSCF exhibits a non-monotonic oscillatory pattern rather than a simple amplitude decay trend.