Experimental and Numerical Investigation of Segment Response to Seismic Wave Propagation for Advanced Geological Detection in Shield Tunnels

Shield tunneling is the predominant method used in underground construction, but it often encounters challenging geological conditions, such as fracture zones and groundwater. Currently, no universally applicable geological detection methods exist, leaving the shield machine to advance in a "blind" state. Notably, the absence of exposed surrounding rock hinders seismic-type detection methods, making it critical to elucidate the response mechanism of segment structures in seismic wave excitation and reception. Therefore, we analyzed seismic wave propagation characteristics of segment-excited/received waves via full-scale experiments and numerical simulations. Results indicate that segment-excited seismic waves achieve resolution comparable to surrounding rock-excited waves, but suffer inevitable energy loss attributed to stress fluctuations within the segment structure. The segment also exhibits an "energy absorption" effect during reception; grouting defects induce increased reflected wave energy, causing cross talk and waveform distortion-linked to stress distribution heterogeneity and discontinuity near the segment. Therefore, we suggest that the geophone could be placed under the tunnel arch in practical to reduce the probability of effects caused by grouting defects, shorten the propagation distance of excited waves in the segment structure along the excavation direction, and use the mechanical source to enhance the excitation energy, so as to improve the effectiveness of adverse geological detection. This study verifies the feasibility of segment-based seismic wave excitation/reception, providing theoretical and technical support for advanced geological detection in shield tunnels.