Study on the damage cause of tunnel junction under different component earthquakes based on on-site investigation and numerical simulation

Abstract

The Shengli tunnel sustained significant damage during the 2022 Luding earthquake (Mw 6.6), with numerous circumferential and inclined cracks observed in the tunnel lining. This paper develops a three-dimensional numerical model to examine the tunnel junction's dynamic responses to three seismic components: east-west (EW), north-south (NS), and up-down (UD). It also analyzes the causes of tunnel damage. A comparison between the numerical simulation results and the on-site investigation findings shows a high degree of agreement, with damages predominantly concentrated at the junction between the right tunnel and the branch tunnel. The tunnel cross sections' plastic damage areas, damage parameters, K values, and convergent deformation are significantly larger during horizontal vibrations (EW and NS components) than during vertical vibrations (UD component). The stiffness differential between the right and branch tunnels results in varying dynamic responses, leading to geometric incompatibility at the junction as the primary cause of damage. Under horizontal earthquakes, tunnels aligned perpendicular to the vibration direction exhibit significant lateral deformations. Consequently, the extent of damage development in the right tunnel is greater than in the branch tunnel under an EW component earthquake, and the extent of damage development in the branch tunnel is greater than that in the right tunnel under an NS component earthquake. In contrast, damage under the UD component is confined near the junction, without extending into the right or branch tunnels. From an energy perspective, the tunnel system accumulates the least inelastic strain energy during UD component earthquakes, resulting in minimal damage despite the highest Peak Ground Acceleration in the UD direction.