Collapse Mechanism of Lining Removal and Treatment Measures in Diseased Tunnel with Complex Geology

To study the collapse mechanism and treatment measures of lining removal in diseased tunnel, a tunnel collapse in Chongqing was taken as an example to record the collapse process. By analysing to the geological conditions, tunnel disease conditions and process of collapse, the mechanism of collapse and its treatment measures were explored. The results show that corrosion, cracking, leakage and other diseases of tunnel lining concrete, loose and broken surrounding rock in the tunnel collapse section and the "structurally weakened" surrounding rock by corrosive groundwater are the main internal cause of tunnel collapse. Under the construction disturbance, the accumulation gravity of crushed stone exceeds the ultimate bearing capacity of the primary support, leading to the cracking of the primary support, and the heavy rain makes the weight of the overlying strata increase, which is the direct cause of the collapse. The way of step excavation is adopted in the process of collapse treatment, the cavity is backfilled by pumping concrete, and the supporting measures such as advanced small pipe, feet-lock bolt and steel arch are used to remove the collapse accumulation and re-cast the lining structure. That can provide reference for similar collapse treatment.