Engineering application of integrated geophysical exploration methods for disaster identification and treatment in thick fault zones of tunnels: a case study of the right tunnel of the West Tianshan ultra-long tunnel

Abstract

Ultra-long tunnels crossing active fault zones in plateau regions are prone to mud inrush, sand gushing, and rockburst, while single-method advance detection may lead to discontinuous identification and missed anomaly boundaries. This study proposes a multi-scale integrated geophysical prospecting framework for continuous hazard identification in thick fault zones. The framework combines methods with different detection depths and physical sensitivities and introduces an overlap-based criterion to improve continuity between adjacent survey windows. In the field application, an overlap length of approximately 20–30 m was arranged between adjacent survey sections to support cross-validation of anomaly boundaries. The framework was applied to the F1 fault zone in the right tunnel of the West Tianshan ultra-long tunnel using seismic acoustic prospecting and ground-penetrating radar. The integrated interpretation identified weak interlayers and mud inrush zones, water-bearing fault zones, and fractured hard rock with potential rockburst. The detected anomalous zones showed good spatial consistency with excavation observations, including the collapse near YK130 + 135.0, the mud inrush near YK130 + 220.0, and a fractured zone with minor seepage near YK130 + 355.0. The results indicate that the proposed framework improves boundary continuity and recognition reliability, providing practical support for hazard identification and treatment zoning in complex faulted ground.