Analysis of the risk of TBM jamming through a challenging geological section at the Brenner Base Tunnel

The mechanized excavation of deep tunnels in low-quality rock-masses often leads to high pressures on the shield, potentially causing TBM jamming. This study analyses the excavation behaviour of a double-shield TBM in a challenging geological section of the Brenner Base Tunnel at significant depth. To investigate the interaction between the rock-mass and the shield, finite element axisymmetric analyses were performed. These analyses were calibrated against monitoring data collected during tunnelling, specifically, shield gap measurements taken by fontimeters and records of gripper extensions. Additionally, a sensitivity analysis was conducted to evaluate the effect of variations in shield length and rock-mass conditions. The results show that the thrust force exerted by the hydraulic jacks in the encountered conditions would have been sufficient to overcome the frictional resistance imposed by the rock-mass pressure on the shield. However, even slight reductions in rock-mass quality or increases in shield length would be linked to a significant rise in thrust demand and a greater likelihood of TBM jamming.