Study On Numerical-Simulation Support Opportunity Of Tunnel Based On The NATM Construction

The stress redistribution of tunnel surrounding rock comes up with the excavation, then the new mass balance is achieved. It’s supposed that surrounding rock plays a synergistic supporting role with tunnel support structure. Furthermore the certain defor-mation is permitted for expressing the self-support capacity of surrounding rock to greatest extent and reducing the load on the support structure. For this reason, the NATM is applied to construct tunnels at home and abroad.The success of NATM is that the support method and time is reasonable. The method includes shotcrete, anchor, etc. It can make characteristic curve of supporting and surrounding rock to intersect at the Pmin point. And the balance of surrounding rock can give full play to the bearing capacity from it. As compared with the NATM, the early traditional supporting structure can’t provide the continuous support resistance or is unable to choose the reasonable support opportunity. Consequently, it will be hard to provide appropriate support resistance towards the Pmin point.In the perspective of the optimization, the best support timing is that the (PD+PR) is maximum to construct the supporting. Under the premise that the strength loss of surrounding rock in protection is enough small, the deformed-released load fully achieves maximum, the bearing capacity of the tunnel arch can achieve the maximum. However, the best support period [TS1,TS2] is proposed owing to the difficult support timing.According to the feature of the NATM construction and the tunnel supporting, the finite element software ABAQUS is used to simulate the construction processes of typical section of tunnel. While the released-load ratio of surrounding rock is different, the mechanical and displacement distribution of surrounding rock and support system are obtained as well as plastic deformation of surrounding rock. The reasonable support opportunity is that self-support capacity of surrounding rock expresses furthest, support system is made full use of, and the resistance of secondary lining is decreased to lowest, meanwhile, guaranteeing that using of support material is reasonable. The thesis analyzes generally and compares surrounding rock, tunnel supporting and anchor in the reasonable support opportunity. Finally, the best support opportunity is determined on the tunnel.