Key Technology Research On Undercutting Construction Of Large Section Passenger Tunnel Under Complicated Environmental Conditions

Based on the New Dali Temple tunnel of newly built Shangqiu-Hefei-Hangzhou Railway(Anhui section)Station project,the key construction technology under complex environment in mountain area tunnel,was analyzed by the finite element numerical simulation,field measurement and theoretical analysis.A reasonable tunnel construction method was determined as the mountain tunnel underneath highway,then the blasting excavation design is improved,finally the construction stability under Dali Temple reservoir was discussed,and the influence of reservoir to the later tunnel operation was studied as well.The main work and achievements are as follows:(1)Aiming at the construction method problem of shallow excavation tunnel underneath highway,the new Dali Temple tunnel under 208 highway was used as an engineering example,the finite element simulation analysis was carried out by MIDAS GTS / NX software,the stress distribution and deformation characteristics of tunnel surrounding rock and supporting structure induced by different construction methods were analyzed,which including two step method,three step method,six step CD method and double side wall guide pit method.Based on the above results,big pipe roof protection system plus six step CD method was recommended for large section passenger tunnel construction under the existing provincial highway,Then it was used to guide this segment construction,and was verified to be rational and feasible by tracking the whole process.(2)The numerical analysis of traffic load influence on the tunnel stability showed vehicle operation had no obvious effect on the surrounding rock,in the tunnel axis intersection,the stress in surrounding rock and supporting structure was varied very small.To ensure the tunnel stability,it is recommended to deal with the hole in the wall rock road width range for construction safety.(3)The tunnel vibration caused by the later highway operations is dicussed,to ensure both provincial and new tunnels do not interact with each other during the operation.This can provide a reference for future highway or railway projects in mountainous areas.(4)For the vibration influence on adjacent buildings caused by tunnel excavation,the tunnel underneath New Dali Temple is taken as an example,the vibration velocity and acceleration of the most dangerous point were analyzed during explosion period,the blasting design was optimized,after making a comparision of two optimization designs,finally the reasonable and feasible blasting design was determined,which can be used to guide tunnel blasting design.(5)To solve the problem of the seepage through reservoir water during the hallow-buried tunnel excavation and later operation,the numerical research on the tunnel stability was studied by considering different permeability coefficients,the failure mechanism of shallow tunnel under water infiltration was revealed.