Rock mass excavability indicator: New way to selecting the optimum tunnel construction method

摘要

The concept of the rock mass excavability (RME) indicator, which the authors found very effective in predicting excavability of rock masses by TBMs using a quantification of TBM performance, is introduced to provide the optimum choice for a tunnel construction method. The RME index is based on five input parameters aimed at relating rock mass behaviour and TBM characteristics: (1) uniaxial compressive strength of the rock material; (2) abrasivity; (3) rock mass jointing at the tunnel front; (4) stand-up time dependent on the excavation method; and (5) groundwater inflow. Development of the RME index involved collecting of extensive data from more than 23 km of tunnels and 387 structural regions along the tunnel length. In the process, a number of statistical correlations have been established between RME and such output parameters as: degree of TBM utilization, advance and penetration rates, and the specific energy of excavation. In essence, the RME indicator features an interaction of rock mass conditions with TBM characteristics, which enables both tunnel designers and constructors to decide on the most effective tunnel construction method, in the early stages of the tunnel project.