Objective For the advance geological prediction of tunnels based on reflected seismic waves, the traditional 2D observation method tends to cause spatial positioning deviations of anomalies. To overcome this limitation, this study developed a 3D seismic wave-based advance geological prediction method according to the actual geometries of tunnels.

Methods Using the technical path consisting of theoretical analysis, numerical simulation, and engineering verification, this study solved key technical challenges including 3D wavefield reconstruction, spatial modeling, and migration imaging in the 3D detection system. Based on the principle of geometric seismology, this study demonstrated the enhancement effects of 3D observation on the detection range and positioning accuracy of anomalies. Then, using the rotated staggered-grid finite-difference (RSFD) method, this study achieved the 3D wavefield forward modeling for tilted transversely isotropic (TTI) media in the full tunnel space, with flux-corrected transport (FCT) technology introduced to suppress numerical dispersion. In combination with the calculation of wavefront traveltimes using the fast marching method (FMM), this study achieved 3D migration imaging using the improved Kirchhoff integral theorem.

Results Field tests in a railway tunnel in western Hubei Province indicate that the 3D advance geological prediction method detected a zone with dense fractures 20 m ahead of the tunnel face (at chainage 412). The anomaly body range detected using the 3D advance geological prediction method decreased by 20% compared to that determined using the 2D method. The result maps of the 3D advance geological prediction allowed for the presentation of the spatial morphology of the anomaly body from multiple perspectives.

Conclusion The 3D advance geological prediction technology based on reflected seismic waves can enhance the spatial positioning capability and interpretation intuitiveness of geological anomalies, providing effective technical support for preventing and controlling geological hazards during tunnel construction.