Jamming of the double-shield tunnel boring machine in a deep tunnel in Nyingchi, Tibet Autonomous Region, China

[Display omitted] •Numerical simulation was conducted to study the shield jamming of Double shield TBM.•The contact relationship between shields and surrounding rocks was studied.•A new criterion for quickly judging shield jamming is proposed.•The rock mass strength, deformation, in-situ stress, and reserved gap were considered. The Duoxiongla tunnel in Nyingchi, Tibet Autonomous Region, China passes through a gneissic formation, with a maximum 830 m thick overburden. The tunnel was excavated by a double-shield tunnel boring machine (TBM) and three shield jamming accidents occurred during the construction, which adversely affected the construction progress. In order to prevent the shield machine from jamming again, numerical simulations were conducted to investigate the shield jamming accidents. In addition, the contact relationship between double-shield and surrounding rocks when the TBM entered squeezing ground and the changes in frictional resistance to be overcome during the excavation process were studied. The effects of injection of lubricants and over-cut on reducing the shield jamming risk were explored. Finally, the jamming criterion was proposed by comprehensively considering the surrounding rock strength, in-situ stress, surrounding rock deformation, and reserved gap. The results show that the sequence of surrounding rocks that come into contact with and squeeze the TBM can be influenced by the gap between shields and surrounding rocks, and the locations where the three shield jamming accidents happened are consistent with the actual advancing lengths of the TBM in the formation with extrusion deformation. The method of injecting lubricants at the contact position between surrounding rocks and shields fails to release the jammed TBM. Over-cut can widen the gap between surrounding rocks and shields, which reduces the risk of shield jamming. The assessment of jamming in the Duoxiongla tunnel based on the established jamming criterion is consistent with the actual engineering excavation conditions and can provide reference for judging shield jamming during TBM excavation in other types of squeezing ground.