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.