Research On Construction Risk Assessment Of Large-scale Shaft Engineering Of Mountain Tunnel

With the continuous increase of national infrastructure investment,transportation has become faster and more convenient.As an important auxiliary construction process of tunnels,tunnel shafts appear more in tunnel projects.Due to the complexity and diversity of the tunnel shaft construction environment,the safety risks faced by engineering construction are getting higher and higher.Once a safety accident occurs,it will have a huge impact on the safety of people’s lives and properties.Therefore,scientific and reasonable risk control and management of safety risk factors in tunnel shaft engineering have important theoretical and practical significance.This article relies on a tunnel laboratory tunnel project in a cave in Wuhan.The strata conditions pass through strong and moderately weathered rock formations and require non-blasting excavation,resulting in high construction period pressure.The cave tunnel is equipped with two exhaust shafts,both of which are deep and large shafts.Construction risk High,the construction safety risk control research of the tunnel shaft project mainly includes the following aspects:(1)Based on theoretical knowledge and field data,this paper decomposes the tunnel and shaft engineering in this article according to actual construction procedures,identifies the risk factors and risk events in each process of tunnel and shaft construction,and establishes a risk evaluation system for tunnel and large shaft construction.(2)Based on the safety risk assessment system of a certain cave tunnel and shaft in Wuhan,a risk assessment model based on Bayesian network and analytic hierarchy process was established.First,use the judgment matrix to determine the weight values of the risk factors at all levels in the analytic hierarchy process model.Second,calculate the probability values of the parent node risk factors in the Bayesian network model and the lower-level indicator risk probability in the analytic hierarchy process based on the expert survey weight method.value.Finally,according to the Bayesian network chain transfer principle and the comprehensive integration method,the risk probability value of the risk accident and the risk probability value of the top event risk accident are calculated respectively.The risk assessment model based on Bayesian network and analytic hierarchy process shows that the risk level of the tunnel and shaft construction process is 4,which belongs to a higher level.Comprehensive and dynamic management of the tunnel and shaft construction process should be carried out,and timely and effective measures should be taken.Measures to prevent accidents.This method can effectively assess the construction safety risk level of tunnels and shafts,and avoid the limitation of using only one risk assessment model.(3)Based on the results of the risk assessment model for tunnels and shafts,failure to cover in time,asymmetric excavation,improper pouring methods,and failure to install waterproof panels are key risk factors for tunnel construction;failure to clear holes in time,backfill material strength not up to standard,and non-reinforced rock formations.Improper arrangement of small pipes and improper concrete mix ratio are key risk factors for tunnel construction.In the actual construction process,the above-mentioned key risk factors should be strictly controlled in accordance with the design specifications and standards,and the probability of their occurrence should be avoided and prevented as much as possible,and the safety risk level of tunnel and shaft construction should be reduced,so as to provide guarantee for subsequent construction operations.To sum up,by improving the risk assessment system of the large-scale shaft engineering of the cave laboratory tunnel,effective risk management measures are proposed to provide a reference for the construction safety risk assessment of other tunnel shaft engineering.