Assessment And Control Measures Of Security Risk During Construction Of Large Section Subsea Tunnel

Because of the infinite seawater above, the complicated surrounding rock and the difficulty in geological exploration, it is hardly to obtain the geological and hydrogeology situation of submarine tunnel engineering before the construction, in which there are many uncertainties, once the risk accident occurred, it would bring serious losses, which are from a construction period delay and investment increase to a great disasters. It is important to establish the risk assessment and control scientific system of submarine tunnel in two aspects of theory and technology by further research and systematic summarization. This paper relies on the Dalian Bay cross-sea channel engineering, researches on the security risk assessment and control countermeasure of the large section submarine tunnel construction, the research achievements are summarized as follows.(1) This paper summarizes the basic concept and features of engineering risk systematically and puts forward the definition of the submarine tunnel construction risk. And many conceptions such as the risk surroundings, the risk factors, the risk accidents and the risk bodies are defined explicitly, at the same time, the features of the submarine tunnel security risk during the whole construction period, the basic trait, the influencing factors and the control principles of core risk in submarine tunnel constructions and the specific processes and methods of risk analysis assessment have also been proposed in this paper, based on these achievements, the risk analysis assessment model and the risk acceptance criteria are established.(2) The consequences of water inrush risk in submarine tunnel construction are divided into life loss, society loss, surrounding influence loss and economic loss(which include the direct and the indirect economic loss), the extension engineering method is used in analyzing the water inrush consequence severity in the F1weathered trough construction of the left line of the Xiamen subsea tunnel in this paper, and the problem that the water inrush consequence severity loss cannot be considered unifiedly has been solved effectively.(3)Based on the usual risk identification methods at home and abroad, according to the relevant data and the similar engineering data of the Dalian Bay submarine tunnel, and combining the trait and difficulties of this project, this paper identifies the security risk of drilling and blasting method, pipe sinking method and shield driving method, analyzes and evaluates the risks of drilling and blasting method, pipe sinking method and shield driving method by using expert investigation, numerical calculation and relevant engineering data research, at last, the paper presents the preliminary risk grades assessment, spread out the likely fatal risks and puts forward the corresponding control measures.(4) Relying on the Dalian Bay Subsea Tunnel, a comprehensive assessment of security risks of the two construction methods, respectively corresponding to two project feasible programmes, was carried out, the corresponding control measures were also put forward. At the same time, the concepts and features of core risk security have been elaborated, the core risks of three different engineering methods undersea tunnels have been analysed. The various impact factors of risks are classified on the basis of extensive investigation and research on the relevant engineering data, the rank evaluation matrix of each factor is obtained according to membership function.The likelihood level and the severity level of the consequences of risks are predicted by using the theory of the fuzzy mathematics and the Extension engineering.Then, it can be proved that the core risks of the program are unacceptable risks,but in the feasible minimum risk limits.Core risk control measures corresponding to three engineering methods have been proposed.(5) Through the analysis of each risk coefficient and comprehensive risk factor of the alternatives,shield, pipe sinking method, drilling,it has been pointed out:Large cross-section subsea shield has such characteristics as uneven hardness, poor formation adaptability, high difficulty of the production of machinery and equipment less experience, and technical risk, safety risk, economic risk are relatively large;Large cross-section immersed tube tunnel has such characteristics as large usage of construction site, large destruction of underwater blasting on the the marine environment, great impact on the maritime shipping of floating, sinking, and environmental risk are relatively large;Large cross-section drilling and blasting method tunnel has such characteristics anlonger continuous driving distance, poor operating environment, big construction risk of bad geological section, and technical risk, security risk are relatively large.The Dalian Bay Subsea Tunnel two positions corresponding to the for comprehensive comparison and selection, recommended the use of immersed tube construction.After comprehensive comparison and selection of the two kinds of construction schemes corresponding to the two line position program of Dalian Bay undersea tunnel, the immersed tube construction method is recommended.