Two Stage Risk Assessment And Countermeasutes Of Long Span Highway Tunnel

As an important part of highway engineering,tunnel engineering has many incomparable advantages,such as improving and adjusting highway linearity,saving construction time,shortening mileage,high adaptability to topography,reducing the damage of ecological environment and so on.Compared with bridge engineering,subgrade engineering and housing construction engineering,many uncertain and complex factors coexist in tunnel construction period,which makes tunnel engineering accidents occur frequently,causing huge economic losses to the country and bringing serious adverse social effects.At the same time,with the development of tunnel construction to super long,long-span and deep buried direction,especially the emergence of large-span municipal engineering tunnel and highway tunnel and other special tunnel projects,further aggravate the risk of tunnel engineering project construction.Due to the differences of environmental,geological and hydrological conditions of tunnel engineering,and the various processes and methods involved in the design and construction of tunnel engineering,the difficulty of safety risk assessment and control of tunnel engineering is further aggravated.Based on this situation,data collection,expert investigation,analytic hierarchy process,finite element method and other methods were carried out to investigate the common risk accidents of long-span tunnel.The main research contents and conclusions are as follows:(1)Through the collection and collation of the previous data,the common risk accidents and the main inducing factors of the tunnel were sumaried systmaticly.At present,the main risk accidents of long-span tunnel are portal instability,tunnel collapse,water and mud inrush.The main risk sources of these three kinds of risk accidents can be divided into five categories: natural factors,engineering geological factors,engineering hydrological factors,survey and design factors and construction factors.At the same time,the risk source database of the five inducing factors was established.Based on the investigation and design data of the project,the risk fault tree of the project is established.(2)Using expert investigation method and analytic hierarchy process,the risk assessment of the two stages of design and construction was analyzed.The main risk grade,risk index and the order of each risk index were put forward.At the same time,the advantages,disadvantages and application of the two methods were discussed.(3)Based on the research results of risk assessment and relevant conclusions,the three-dimensional finite element method was used to calculate and analyze the safety and stability of tunnel structure and its surrounding environment under different lining structure forms,different surrounding rock softening degree,different side heading spacing under different lining structure forms and tunnel intersection construction conditions.The results showed that the displacement of surrounding rock and supporting structure can meet the requirements of the specification when the surrounding rock reinforced lining structure or surrounding rock composite lining structure is adopted in the construction stage.When the pillar rock of the tunnel is excavated,the vault settlement is the largest,which is the most dangerous construction step.The distance between left and right heading should not be less than 5m during the construction of reinforced lining structure section of surrounding rock.The distance between left and right heading should not be less than 3m during the construction of reinforced lining structure section of surrounding rock.Based on the above analysis results,the proposed measures for supporting project construction are put forward,and the tunnel safety risk is reassessed after the implementation of the proposed construction measures.