Engineering Safety Risk Analysis And Control Of Subsea Tunnel Constructed By Drill And Blast Method

ABSTRACT:With the development of economy and the demand of traffic, as an important means of transportation, the subsea tunnel has attracted more and more attention around the world. Because of the infinitude of the ocean above, subsea tunnel construction brings us new challenges and risks, which are different from usual mountain tunnels. On the basis of massive researches on safety risk in underground structure construction, it shows that the safety risk in construction phase contains both its own risks with phased characteristics and the cumulative risks from planning phase and designing phase. If the safety risks of former phase are not evaded effectively, they are surely to add to the following phase and form cumulative risks. The evasion of phase risks is easier, while the evasion of cumulative risks is much more complex and difficult, and even can not be evaded. Therefore, safety-risk researches in subsea tunnels, which are constructed by drilling and blasting method, should be started from the whole constructing process, and engineers should fully consider both the own safety risk during every construction phase and its cumulative effect to the following phase, and evade all the risks promptly to reduce the safety risk of a tunnel project.This paper takes planning, designing and constructing phases of drilling-blasting subsea tunnels as construction scope of the research, and safety-risk analysis of water-inrush as the scope of risk research. Based on the projects of Xiamen XiangAn subsea tunnel and Qingdao JiaoZhouWan subsea tunnel, the following five aspects are carried out by using theoretical analysis, numerical simulation and field measurement methods..(1) Establishment of safety-risk management system for the whole construction process of subsea tunnel. According to the risk characteristics of subsea tunnels, this paper puts forward the idea of safety risk management in the whole construction process of subsea tunnels; introduces the concept of "core safety risk" and "cumulative risk"; refers relevant knowledge of risk management at home and abroad, and establishes safety-risk management system for the whole construction process of subsea tunnel;(2) Analysis of subsea tunnel water inrush based on rock deformation control. By analyzing the pattern and mechanism of water-inrush in subsea tunnel, it is considered that water-inrush in subsea tunnel mainly originates from big deformation due to tunnel excavation, and then the paper makes a major discussion on the relationship between safety risk of water-inrush and the tunnel crown settlement. Setting the left line F1 weathered trough section in Xiamen XiangAn subsea tunnel as project background, this paper establishes the crown settlement for safe construction of subsea tunnels, and makes out the safety control target of settlement in every construction phase;(3) Analysis of safety risk environment and risk factors of full-process for subsea tunnel. Beginning with the analysis of safety risk environment in the whole construction process of subsea tunnels, this paper makes detailed analysis and differentiation for safety risk factors of the risk environment in the planning, designing and construction phase of the subsea tunnels, and determines core safety-risk factors;(4) Analysis and prediction of water inrush safety risk for subsea tunnel. Based on the result of comprehensive evaluation for safety risk factors, taking the left line F1 weathered trough section in Xiamen XiangAn subsea tunnel for example, the paper makes a comprehensive evaluation on the occurrence probability of water-inrush safety risk in weathered trough section by using the fuzzy comprehensive evaluation; applies Expandingable Engineering Method to assess the consequence loss of water-inrush safety risk; makes grade division of the water-inrush safety risk in the weathered trough section, and confirms the safety risk scale of water-inrush in the weathered trough section.(5) Study of control technology of water inrush safety risk for subsea tunnel. According to the characteristics of safety risk in every phase during the whole construction process, the relevant control technology of safety risk is put forward in this paper from technical view.