Understanding the impact of the earthquake on circular tunnels in different rock mass: a numerical approach

Tunnels are the most important infrastructure components as it plays a major role in public infrastructure, water transport and the production of hydroelectric power. The constant variation in the geological conditions affects the tunnel stability which can be achieved using flexible rock support methods. The analysis and understanding of the prevalent complex rock mass in a region which is highly seismically active is a challenge and necessary for the successful execution of any tunnelling project. Therefore, a pseudo-static approach has been studied to understand the impact of earthquakes on circular tunnels using the Phase 2 software. The rock mass surrounding the tunnel is modeled using the continuum approach and continuum with interface approach where joints were incorporated in the model as an interface. For this study, a tunnel model with specification (diameter-6 m, depth-100 m) with a Q range of 1-30 was used to examine the impact of rock mass quality. The study revealed that while the seismic load remains unchanged, the magnitude of the axial force on the liner and the net increase due to seismic loading referred to as seismic axial force, increase as the rock mass quality decreases. The diameter of the circular tunnel at a depth of 100 m is increased from 6 to 24 m at an interval of 6 m to check the influence of the tunnel diameter under the seismic loading. It was observed that the seismic axial force decreases with the tunnel diameter for the rock mass Q = 1 (very low rock class) and strong rock, it is comparatively small.