Research on Collapse Mechanism of Tunnel Portal Shallow Burying Segment of Center Diaphragm Construction Method and its Treatment

The surrounding rock of Bijia mountain tunnel portal shallow burying segment mostly fractured, the level of these rock are V and VI. Serious collapse accident was happened during the tunnel excavating. Besides, the reason and mechanism of collapse is discussed by analyzing site monitoring displacementtime curves, surrounding rocks, construction method and inclement weather. After the collapse body stability, combined with the actual situation to choose reasonable management plan, after the governance, through analysis the field monitoring curves to inspect the feasibility of the scheme. From the result of operation, the treatment plan had been done well, the construction of tunnel was safety and stability.