Seismic response of tunnel intersections in jointed rock mass within underground research laboratory: A coupled DEM–DFN approach

The stability of tunnels in jointed rock masses can be compromised by seismic activity, making it important to understand the characteristics of waves and rock joints. This study investigates the dynamic response of two intersecting tunnels under varying input wavelength and amplitude and the influence of joint density and stiffness on their behaviour using the DEM–DFN approach. A discrete fracture network (DFN) interlay was incorporated into a distinct element method (DEM) model domain to simulate weak zones in rock masses. Analysis shows that higher fracture density reduces shear stress near the DFN interlay, while joint stiffness affects wave transmission, causing a significant drop in shear stress upon wave entry. The increase in joint density and change in interlay thickness intensified the amplification of reflected waves, resulting in wave interference and reduction in transmission waves. For tunnel intersections within the DFN interlay, the larger of the two tunnels, or the main tunnel, experienced substantial deformation when peak ground velocity (PGV) was between 0.05 and 0.25 m/s, while the smaller or access tunnel exhibited maximum displacement only when PGV exceeded this range. Amplification of waves was significant when the ratio of wavelength to tunnel diameter ( λ / D ) was 10, while λ / D > 75 produced a response similar to uniform quasi-static loading. Tunnel joints with stiffness exceeding 100 GPa/m experienced substantially lower deformations, while those with higher fracture volumetric intensity ( P 32 = 2 m 2 /m 3 ) led to reduced wave propagation. The size of the intersection also influenced the deformation of both tunnels, with larger intersections resulting in greater deformation. Research highlights The study examines wave propagation through discrete fracture network interlay of varying thickness Dynamic response of intersecting tunnels in jointed rock mass simulated using coupled distinct elements and discrete fracture networks. Investigation of the impact of wavelength, amplitude, joint density, and stiffness on tunnel intersection behaviour.