Real-Time Estimation Method for Tunnel-Excavated Rock Strength Based on TBM Parameters

The tunnel boring machine (TBM) is widely recognized for its advantages of speed, efficiency, and environmental friendliness; however, the observation and evaluation of the excavated rock surface are rendered difficult because of the TBM design defects. To improve construction efficiency and safety, it is crucial to study the real-time estimation of tunnel-excavated rock strength. In this study, the TBM data from Chongqing Metro Line 9 of the Zhongcong Tunnel showed that the thrust force (force normal to the rock surface) F-N is proportional to the cutting depth per revolution P, and the torque of the cutting rock T-R/thrust force F-N is proportional to P-0.5. According to the engineering practice of the Zhongcong Tunnel and previous studies, we developed a real-time estimation method for tunnel-excavated rock strength based on three TBM operating parameters: F-N, T-R, and P. A statistical analysis of the construction data of 17 TBM rock tunnels showed that the two dimension parameters & gamma;(1) and & gamma;(2) of the estimation formula are correlated with the cutter diameter d/tunnel diameter D and number of cutters n. The results of the fitting analysis were used to obtain the calculation methods for & gamma;(1) and & gamma;(2). Subsequently, the proposed formula for rock strength estimation was applied to both the Zhongcong Tunnel (soft rock) and the Maiko Tunnel (hard rock), and the generalizability and reliability of the estimation formula were verified. The results provide a more practical and feasible approach to estimating excavated rock strength in real time. Meanwhile, the proposed method has an important application value as it can improve the efficiency and safety of TBM tunnel construction.