Impact of Overcut on Interaction Between Shield and Ground in the Tunneling with a Double-shield TBM

Excerpt

Double-shield TBMs (DS-TBM) are among the most technically sophisticated excavation machines in use by tunneling industry. The use of shields around the TBM allows the machine to pass through weak grounds and adverse geological conditions. However, there are limitations in applicability for DS-TBM in some ground conditions where large deformations are anticipated. The presence of the shield limits access to the tunnel walls for observation of ground conditions. This means limited possibilities of observing and analyzing ground conditions to avoid certain problems. Similarly, the presence of the shield does not allow the intrusion of the ground into the tunnel envelope, which is the main objective of using a shielded machine in the first place, yet it also creates the possibility of ground pressing against the shield. In such conditions, TBM may get stuck (including shield jamming and cutterhead blocking) in complicated geological structures, especially under high ground cover or in weak rocks, where large convergences are expected. This could cause major delays and impose a heavy and expensive burden on the tunneling operation. Some of the issues related to application of DS-TBMs in squeezing ground have been discussed in Hasanpour (2014) and Hasanpour et al. (2014a, b) and some possible scenarios and concepts for mitigating the related problems are offered. …