Study On Water Inrush Risk And Early Warning Mechanism Of Karst Tunnel

Accompanying the enforcement of strategy to develop western regions, transport, energy and other infrastructures of western China expand substantially and the long tunnel construction in karst zone increases dramatically. In the process of long tunnel construction, geological hazards such as water inrush and mud outburst, rock burst, gas, and etc. often occur. Water inrush and mud outburst are particularly serious which often lead to destroyed equipments and delayed construction, even cause casualties and economic losses. Water inrush risk evaluation and early warning have been the issues that require to be solved urgently.There are several underground rivers in the area of Wuchiba Tunnel and the groundwater level is about 150m. It is about 2-4km near to Maluqing Tunnel in the same hydrology geology unit. Qiyueshan Tunnel crosses Qiyueshan anticline, two faults and two underground rivers. The groundwater level is about 100m. It is at the same hydrology geology unit with the Qiyueshan Railway Tunnel which had occurred water inrush many times. The karst is very developed in the area. Longtan Tunnel crosses three faults and Qinchunhe Underground River. The groundwater level is about 100m. All the tunnels mentioned above have seriously water inrush risk. To ensure the safety of tunneling and operation, according to the high risk karst tunnels of Hubei Hurongxi highway, the water inrush risk and early warning mechanism were studied and some meaningful results were obtained by applying the method of karstology, geology, geophysical exploration technique.The basic karst development rule was analyzed based on studying the literatures and doing research. The main controlling factors of karst development, which are affected by stratum lithology, underground water hydrodynamic zoning, geological structure, landform and etc., were mentioned. Through implementing water inrush geological disasters controlling research on the high water inrush risk tunnels of Hurongxi highway and researching karst water inrush into tunnel disasters of Yichang-Wanzhou Railway, the basic law of karst development of the highway was studied and the main types of water storage structures along the highway were proposed.Water inrush into karst tunnel is comprehensively influenced by various factors and karst tunnel water inrush risk evaluation is still at the starting stage. The main basis of water inrush is proposed and the evaluation index system is established based on the research on main influence factors of water inrush into karst tunnel. The weight of index is obtained by AHP (The Analysis Hierarchy Process) and the membership degree is gained by statistical methods. The water inrush risk is evaluated by fuzzy comprehensive evaluation method. The risk is quantized by the fuzzy comprehensive evaluation method.The high risk water inrush scope given by the risk evaluation means is large. To reduce the scope, it is necessary to establish the identification of risk sources system which is comprehensive advanced geological forecast. At different risk grading part along the tunnel, different programs on identifying the water inrush risk sources are made. The key locality of water inrush can be found for the early warning indexes monitoring.Early warning mechanism of water inrush into karst tunnels is one of the most important means for disaster prevention and reduction. The early warning grading was devided into four classes, which was represented by red, orange, yellow and blue according to the damage, emergency degree and development situation. The early warning mechanism flow and early warning publishing procedure is made according to the characteristics of tunneling. The early warning indexes system is established. The standard of each index is put forward and the warning degree and warning limit of water inrush are proposed. Different pre-control measures are mentioned for different warning grade.The emergency plan is formulated to reduce the damage of water inrush. The law of water flow in tunnel when water inrush into tunnel was analyzed and the escape route was optimized. According to the actual construction situations, the emergency training scheme was made and emergency training was implemented with basis of disaster prevention and reduction.In the construction of Wuchiba Tunnel, Qiyueshan Tunnel, Longtan Tunnel and etc., water inrush risk evaluating, identification of waterinrush risk sources and four color early warning were implemented. Losses caused by water inrush and mud burst were avoided and decreased many times by implementing the results.The construction safety and construction period were guaranteed.