Research application of overcasting and three-dimensional analysis of feature data in deeply buried tunnels

Abstract

As a critical component in the construction of diversion-type power stations, water diversion tunnels require comprehensive advanced geological prediction to ensure safe water diversion tunnels require comprehensive advanced geological prediction to ensure safe excavation and timely completion. This study focuses on a deep-buried water diversion tunnel in western Sichuan, where complex geological conditions such as high in-situ stress, fault fracture zones, and abundant groundwater were encountered during excavation. By integrating geological analysis, TRT(Tunnel Reflection Tomography) method, Transient Electromagnetic Method(TEM), and Ground Penetrating Radar(GPR), we propose a three-dimensional geological prediction approach based on an advanced geological forecasting platform. The implementation procedure consists of three phases: First, 3D seismic wave method is employed to identify tunnel sections with anomalous geophysical responses indicating unfavorable geological features. Second, multi-angle TEM verification and three-dimensional integration of geological and geophysical data are conducted for these anomalous sections. Finally, precise prediction of adverse geological conditions ahead of the tunnel face is achieved through GPR detailed detection and supplementation of prior geological data. Application of this method in the western Sichuan tunnel project revealed: In the section Stake(Tunnel) 6+950—6+867, surrounding rocks exhibited poor integrity with developed joint fissures, localized minor faults, moderately fractured to fragmented rock masses, and significant groundwater presence, classified as Class IV surrounding rock. The section Stake(Tunnel) 6+867—6+830 showed relatively poorer rock integrity with moderately developed joints, less groundwater, and localized fracturing, classified as Class III₂—IV surrounding rock. The result demonstrate that this 3D comprehensive geological prediction method effectively combines geological and geophysical approaches, integrating point-line-plane geophysical techniques. It successfully delineates the spatial distribution and development range of unfavorable geological features including fault fracture zones, joint fissures, and water-rich zones ahead of the tunnel face, providing reliable technical guidance for safe and efficient tunnel excavation.

Keywords

3D advanced geological prediction / geophysics / geological informatization / deep-buried tunnel / unfavorable geological features