Dynamic response and performance enhancement mechanisms of tunnel buffer layers under mainshock-aftershock sequences

Under mainshock-aftershock sequences, tunnel linings exhibit damage accumulation and delayed failure characteristics. Based on large-scale shaking table tests and numerical simulations, this study systematically investigates the dynamic response and damage evolution of tunnel linings, with particular emphasis on the seismic mitigation mechanism of a buffer layer. Results indicate that shear-dominated initial damage first develops at the spandrel and arch springing during the mainshock, while subsequent aftershocks accelerate damage accumulation and promote delayed crack coalescence. The buffer layer reduces peak acceleration, alleviates local strain concentration, and transforms the lining response from an inertia-dominated mode into a globally coordinated deformation mode, thereby suppressing secondary stress amplification during the aftershock stage. Energy-based analysis using Arias intensity further reveals a three-stage energy regulation behavior of the buffer layer. Parametric numerical analyses identify the optimal stiffness ratio and thickness ratio for enhancing the seismic performance and damage resistance of tunnel linings under mainshock-aftershock loading conditions.