Abstract: The construction of mountain tunnel can not completely avoid the large deformation disaster. After tunnel invasion, the improper timing of the deformed first liner replacement will not only delay the construction period, but also possibly cause the secondary damage, such as tunnel collapse. Taking the collapse event of Anqicun No. 1 tunnel in Yunnan Province as the background, after the large deformation of the tunnel and the application of the temporary steel support, the stress curve and the stress-deformation relationship of the rock and support are analyzed based on the convergence-confinement principle. The influence of different treatment timing on the stress of rock and the failure of rock block and joint in large deformation tunnel is analyzed using the discrete element software 3DEC. In this model, the deformed first liner is replaced when the settlement of the tunnel reaches 70%, 75%, 80%, 85%, 90%, 95% and 100% of the final displacement(the displacement when the deformation rate less than or equal to 0.2 mm/d). Then, the stress distribution, the amount of rock destruction and the area of joint failure are statistically analyzed. The results show that when the displacement of the vault settlement reaches 90% of the final displacement, the rock stress is almost as same as it reaches 100%. After the deformed first liner replacement completed and the tunnel become stable, the joint destruction area when replace in 90% is less than replace at 100%, and the rock failure amount are almost the same as replace at 100%. Therefore, the treatment can be carried out before the displacement reaches the final displacement. This research can not only improve the safety of large deformation treatment process, but also greatly reduce the treatment time, which has important reference value for research and construction.

Key words: tunnel large deformation, convergence-constraint, discrete element, treatment timing