Theoretical and numerical responses of deep-buried diversion twin tunnels with imperfect interfaces under blasting or seismic P- and SV-waves

Abstract

Close-distanced underground structures in deep engineering generate pronounced interaction under dynamic perturbation. The work presented in this paper focuses on theoretical and numerical scattering and diffraction of blasting or seismic P-and SV-waves by deep underground diversion twin tunnels in a full space, which considers the mutual interaction of deep-buried tunnels. Based on wave function expansion method, modified Graf’s addition theorem, imperfect interface model and Fourier synthesis method, the time-domain responses of surrounding rock, liner and fluid were evaluated theoretically. The theoretical results indicated that dynamic stress concentration areas were approximately perpendicular to the perturbation direction for the transient P-wave disturbance. The stress concentration areas approximately rotated clockwise and counterclockwise 45o by the disturbance direction for the transient SV-wave perturbation. When the center-to-center distance between deep-buried twin tunnels exceeded eight times the maximum excavation radius, mutual interaction triggered by dynamic disturbance can be neglected. A self-developed software incorporating free-field boundary conditions, namely Cellular Automata Software for engineering Rock mass fracturing process (CASRock), was presented and employed to investigate effect of fluid content on dynamic responses. Finally, elasto-plastic numerical analysis in Neelum-Jhelum hydroelectric project subjected to seismic loads was presented. The results can provide theoretical basis for the seismic design and deep underground reinforcement.