Metros are mass rapid-transit systems that have helped solve commuting problems for residents of metropolises throughout the world. However, adverse geological structures, leading to problem such as water inrush and mud gushing, pose a major threat to metro construction. Geophysical survey techniques provide quick and relatively inexpensive ways to detect adverse geological structures ahead of the tunnel face. Left line of the R3 metro tunnel in Qingdao, China will pass an aquifer sand layer under the Wolong River. To map the geological conditions below the river, we proposed a comprehensive prospecting method that would combine the merits of surface electrical resistivity imaging (S-ERT), seismic ahead prospecting, and tunnel-face and borehole electrical resistivity imaging (TBERI). The prospecting scheme was effectively revealed in a numerical model analysis, in which the stratum distribution was reconstructed using S-ERT. Field tests validated the synthetic results. The ahead prospecting scheme was able to reconstruct the distribution of an aquifer sand layer. Based on the results obtained, we believe that, the proposed scheme could play an important role in metro tunnel construction.

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