Comprehensive ahead prospecting for hard rock TBM tunneling in complex limestone geology: A case study in Jilin, China

Tunneling in karst strata using tunnel boring machines (TBMs) presents numerous challenges. The unpredictable occurrence of fractured zones and water bearing structures ahead of tunnel face might cause tunnel collapse or water inrush hazards. This paper describes the successful application of comprehensive ahead prospecting in TBM tunnel to identify adverse geological bodies in Jilin, China. In the study area, TBM excavations were performed in limestone strata significantly influenced by groundwater and faults. The comprehensive investigation mainly included in-tunnel seismic and resistivity methods. First, seismic ahead prospecting was performed to detect fractured zones. Then, to investigate the water bearing condition of the fractured zones thus identified, resistivity ahead prospecting was applied three times continuously with a dynamic design. To effectively use the prior information obtained, initial model and inequality constraints were applied in resistivity inversion. A joint interpretation idea was realized by the effective use of prior information in this case, supporting the improvement of inversion reliability and reduction of non-uniqueness. A fractured zone and two water-bearing structures were successfully predicted. Based on this case study and the lessons learned, we suggest a comprehensive prospecting method to ensure safe TBM tunneling through the study area.