Application of the comprehensive forecast system for water-bearing structures in a karst tunnel: a case study

While tunneling in karst terrains, engineers may encounter unpredictable well-developed karst conduits, which frequently lead to water inrush accidents. Geological processes significantly affect the varieties and characteristics of water-bearing structures. Therefore, a comprehensive system for water-bearing structure prediction is first put forward, and then the geological and hydrogeological engineering conditions of the Yuelongmen tunnel in Southwest China are analyzed. To accurately predict the geometric characteristics of water-bearing structures and their spatial relationship with the tunnel face, the transient electromagnetic method (TEM) and ground-penetrating radar (GPR) were comprehensively applied. Then, the induced polarization method (IP) was utilized separately to detect the three-dimensional position and spatial distribution pattern of the water-rich area. According to the comprehensive forecast conclusion, targeted boreholes were drilled, which were selected to verify the water-bearing structure in the survey area. The drilling and detection results matched. Furthermore, the curtain grouting method was adopted for the treatment of the water-rich area. By establishing a comprehensive prediction technology system with the principle of from qualitative analysis to quantitative identification, from structure locating to the water-bearing structure discrimination, as well as from far and near, this comprehensive prediction system was successfully put into practice in the karst tunnel in Sichuan; it can play a guiding role in similar projects.