Analysis And Application Of Mutation Problem Of Surrounding Rock Pressure In Highway Tunnel Under Different Burial Depth Conditions

With the construction of highway,railway and urban rail transit projects in China,the tunnels,as the important part of transportation engineering,more and more have been built,the construction environment becomes more and more complicated.Previous surrounding rock pressure calculation method of statistical data based on railway tunnel collapse and the design method of the tunnel engineering analogy have been unable to fully reflect the large span highway tunnel complex mechanical properties,and difficult to meet the demand of engineering construction,because the sample statistic analogic confined to basic span of 5m span railway tunnel.The most fundamental and most important surrounding rock pressure calculation method in design specification of highway tunnel,the calculation results in critical problems buried deep in the pressure value mutation,lead to engineering design of the tunnel buried deep in the critical depth is difficult to determine when the surrounding rock pressure value.Therefore,in view of different span and different grade of surrounding rock under the condition of highway tunnel,the pressure of surrounding rock under different buried depth is,the change rule of development more reasonable calculation method of the pressure of surrounding rock has become a problem to be solved.In this paper,on the basis of summarizing the variety of surrounding rock pressure calculation method,the state of discrete element software is adopted to different buried depth and span,different circumstances surrounding rock grade highway tunnel excavation is simulated,and calculated according to the height of the cave arch loose surrounding rock pressure,different embedded depth of tunnel surrounding rock pressure calculation method is discussed.The main research work and results are as follows:①Summarizes the factors influencing surrounding rock pressure and a variety of empirical formulas of surrounding rock pressure,the theory method,comparison and analysis of each method under different conditions the change rule of surrounding rock pressure value obtained,made clear the applicable condition and shortcomings of each method;Under different buried depth is analyzed highway tunnel surrounding rock pressure mutations,and to avoid critical deep buried tunnel buried depth pressure of surrounding rock mutations problems as the principle,put forward the shallow buried tunnel by bill bauman,deep buried tunnel surrounding rock pressure calculation method of platts method.②The UDEC tunnel model with different span,depth and surrounding rock level is established,and the mutation range and the correction method of surrounding rock pressure value are proposed.Element analysis in this paper,based on the state of the Ⅳ,V loose surrounding rock under the condition of tunnel pressure under the condition of different depth change rule,the numerical simulation results show that when the tunnel buried depth is large enough above can form cave arch,with buried depth continues to increase,the tunnel cave arch height decrease,eventually to maintain within a range.③Based on the wanning tunnel in Hezhou,Guangxi province,we consider to modify surrounding rock pressure of the left line of wanning tunnel,and use Midas GTS NX to numerical simulate the construction process of the left line of wanning tunnel,proved the practicability of the proposed method in this paper.