Mechanical properties and fracture evolution of tunnel surrounding rock under the coupling effect of static and dynamic loads

Abstract

Deep tunnels are often subjected to the combined effects of high geostress and dynamic disturbances, which results in more complex mechanical properties and failure modes compared to shallow tunnels. To study the failure characteristics of tunnel surrounding rock under static-dynamic coupled loading, dynamic tests were conducted using a typical split Hopkinson pressure bar (SHPB) apparatus at different strain rates. The fracture process was recorded using a high-speed camera, and the surrounding rock’s strain field evolution law was analyzed using digital image correlation (DIC) technology. Moreover, a series of numerical simulations under static-dynamic coupled effects were performed using the LS-DYNA software. The results indicate that as the strain rate increases, the main failure mode of the tunnel shifts from tensile failure to shear failure. Lateral pressure significantly suppresses the width and length expansion of cracks, while axial pressure promotes crack propagation, leading to an earlier crack initiation time and triggering more secondary cracks. The study also reveals that the lateral pressure coefficient (k) has an obvious inhibition on the tunnel damage process. Finally, through the analysis of the dynamic stress concentration factor (DSCF), it is found that the existence of confining pressure affects the stress concentration distribution of surrounding rock. The findings provide theoretical support for a deeper understanding of tunnel failure mechanisms and the optimization of tunnel design.

Keywords

strain rate / split Hopkinson pressure bar / static-dynamic coupling / crack propagation / dynamic stress concentration factor

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