Abstract: In TBM excavation, the composite rock strata are often encountered, in such a case, it is not easy to estimate surrounding rock strength during tunneling where the tunnel face and wall tend to collapse. For improvement of tunneling efficiency and disaster prevention, it is necessary to estimate surrounding rock strength in real time. Based on laboratory tests and field data in the construction of Chongqing Railway Line 9, it was found that the thrust F_N is proportional to rock strength, it was also found that the ratio of the torque force to thrust, T/F_N were proportional to p^0.5 (penetration p). In this study, for composite rock strata(including sandy mudstone, sandstone and limestone) surrounding tunnel, a method that can quickly estimate surrounding rock strength from thrust and torque measured in-site, was developed. The method can estimate rock strength in real time with two constants α₁, α₂ which can be obtained by linear fitting of the field data for TBM. The method had been already applied to more than ten tunnels. It was found that two constants were only related to the number of disc cutters n and cutter-head diameter d for this geological environment of composite rock strata. The results provide a more practical and feasible idea to estimate surrounding rock strength in real time, and also can improve the reliability and safety of tunnel TBM construction.

Key words: composite strata, TBM, surrounding rock, real-time estimation, reliability