TBM selection method based on threshold evaluation of adverse geological conditions

To address the difficulties in TBM selection and configuration for deep-buried, super-long, and oversized water conveyance tunnels, we proposed a TBM selection method based on threshold evaluation of adverse geological conditions, in which four types of adverse geological factors were graded, including ultra-hard rock, rock burst, fault fracture zones, and large-deformation surrounding rock.Reasonable threshold values were determined according to proportion of different adverse geological conditions, and based on this the adaptability of TBM and type selection could be realized.Focusing on a section of the Yangtze River to Hanjiang River water diversion project, the geological conditions along the tunnel were preliminarily classified for TBM suitability according to relative codes.We gave scores to different varieties of TBMs by the proposed method, and through giving considerations of construction safety and construction period guarantee, a single-shield TBM was identified as the optimal solution for this section.Furthermore, specific configurations were proposed to address critical geological hazards such as water/mud inrush, ultra-hard rock, and large-deformation soft rock, including the installation of an advanced geological forecast system, using forged thick plate strengthen the cutterhead with radial expansion function, as well as enhancing thrust-torque capacity of the selected TBM.These findings provide practical references for TBM selection and configuration in analogous geological conditions.