Geologic forward prospecting using improved tunnel-seismic-while-drilling method: A case study of the water supply project at Songhua River, Jilin, China

Unexpected geologic heterogeneities in tunnel lines often cause safety issues and economic losses during excavation using tunnel boring machines (TBMs). Therefore, collecting geologic information ahead of the excavation front is important to prevent geologic disasters and ensure excavation safety. To predict the geologic conditions ahead of the TBM-excavated tunnel in the water supply project at the Songhua River in China, the tunnel-seismic-while-drilling (TSWD) method was adjusted and then applied. First, common-source gather data were acquired to record TBM drilling noise (pilot signal and seismic waves); a processing approach (including normalization. crosscorrelation, wavefield separation, and migration) was used to image the major relevant geologic heterogeneities ahead of the excavation front. A synthetic study from a numerical model with a fault verified the feasibility of the modified TSWD method to identify and image geologic interfaces. Then, this method was applied to field data resulting from a TBM tunnel excavation project. The field test of the modified TSWD in the TBM tunnel revealed fractured zones, fault boundaries, and a preexcavated tunnel ahead, providing the required geologic information for TBM tunneling and preventing geologically-caused safety issues.