Construction permit mechanism of karst tunnels based on dynamic assessment and management of risk

Jigongling Tunnel of Fanba Expressway passes through strong karst aquifer of Cambrian Shilongdong Fm,and water table is about 150~200 m above the tunnel floor.Large-scale water inrush and mud irruption are easy to happen.In order to control construction hazards,the karst development characteristics of the tunnel site are studied.The risk surroundings,factors and dynamic management for water inrush and mud irruption of the karst tunnel are analyzed.Preliminary,secondary and dynamic risk assessment models based on the comprehensive weights and the expert scoring method are established.A new management mechanism of construction risk,which is a kind of construction permit mechanism based on risk assessment of water or mud inrush,is developed and successfully carried out for the first time.This mechanism not only can be used for the risk management of karst tunnels,but also for other kinds of engineering constructions.It is successfully applied in the karst risk management of Jigongling Tunnel on the line of Fanba Expressway,and it is being employed to manage the construction risk of karst,and the large deformation of soft rock and collapse in Yichang-Badong Expressway.