Obstacle forecasting for tunnel construction using reflected seismic waves

Tunnel Boring Machines (TBMs) are efficient tools for mining tunnels through different types of soil and rock layers, particularly in complicated city areas. TBM tunneling can be risky due to underground obstacles such as building foundations, sudden geological changes, and water-bearing regions. In order to ensure maximum safety during tunneling, it's crucial to utilize a geophysical method to predict the potential hazard ahead of the tunnel. The seismic method would be a perfect selection for this application. However, as the air-solid free surface exists, the seismic look ahead method relying on body waves has to plug the receivers deep into the tunnel wall to mitigate the influences from surface waves, which increases the risks of damaging the concrete tunnel wall and surrounding rocks. This study discusses the potential of using surface waves to detect the obstacles ahead of the tunnel by simulating the wave propagation mode in and ahead of the tunnel. Our simulation results indicate that both active source and passive surface seismic look-ahead methods effectively detect geological changes ahead of the TBM and demonstrate that the surface wave look ahead method has a good directionality in the detection.