Analysis Of Construction Impact Of Bilateral Proximity Tunnel In Bias And Safety Evaluation Research

With the economic development of various cities,the existing railway line network cannot meet the needs of existing development,so new railways are constantly being planned and constructed.Due to the influence of multiple factors such as terrain,geology,ecological environment,urban layout,and economic effects,railway tunnel selection occurs frequently in complex working conditions,and biased terrain appears in Wudiao Village,Jianning Section of Pumei Railway The case where the existing two-line tunnel is adjacent to the left and right sides of the newly-built single-line tunnel.The biased terrain makes the in-situ stress on both sides of the tunnel asymmetrically distributed,and the surrounding rock stress has changed many times under the combined action of tunnel excavation and support.At present,it is not clear how the two new tunnels will affect the existing tunnel However,there are few studies on the two sides of the existing biased terrain,so it is necessary to study the safety impact of the new tunnel under the biased terrain on the existing tunnel.The thesis starts research from the following aspects:Firstly,from the perspective of topography and excavation methods,we will introduce the overview of Wudiao No.1 Tunnel and Wudiao Tunnel on the newly constructed sparse line of the Pumei Railway,and investigate the defects of the existing Wumei Double Line Tunnel of the Pumei Railway.Information on the stress of the side walls on both sides,the defects and problems of the existing tunnel,and so on,to explore the safety protection technology of the newly-built tunnel on both sides of the operating tunnel.Then,with the help of FLAC3 D large-scale finite element numerical simulation software,starting from three aspects of different bias burial depths,bias angles,and longitudinal spacing of new tunnels,14 working conditions were set for each category.Analyze the different excavation sequence conditions.After the left and right tunnels are excavated,the effects on the displacement increment,stress increment and difference of the existing tunnels will be affected.The stress increment ratio is newly defined to quantitatively judge the bias of existing tunnels under different working conditions.Summarize the more suitable burial depth,bias angle and longitudinal spacing,and put forward suggestions on a reasonable excavation sequence.Further through on-site investigation,literature reading,numerical simulation test,multilevel and multi-factor considerations affect the safety index of existing tunnels,build a safety evaluation system for high-speed railway tunnels with double-side proximity operation,based on AHP-cloud model for the existing tunnel K227 + 439～ K227 + 600 a total of 161 m in five intervals was used for safety risk assessment.Through research,the main conclusions are as follows:1.The investigation of three types of diseases,such as lining spalling,lining leakage,and lining cracks,found that the tunnel structure is relatively complete and there is a small-scale variation that does not develop.Some tunnels have extremely serious diseases.According to the existing tunnel safety assessment criteria,the soundness is judged to be B level.2.The effect of different buried depths,different bias angles,and different longitudinal spacings on existing tunnels on the two-sided adjacent tunnels with biased terrain is shown by the results.When the other engineering conditions are the same,the buried depth is 20 m ～25m,and the bias angle is At 25 ° ～ 30 °,the displacement and stress increment of the existing tunnel are relatively small,and the reasonable excavation sequence is: first excavate the right side of the deep hole and then excavate the left side;for the longitudinal spacing,the reasonable Longitudinal spacing is 30 m ～ 40 m,either excavate large tunnel on the right side first or excavate small tunnel on the left side first.3.Constructed a safety evaluation system for high-speed railway tunnels with doublesided proximity operation.The safety evaluation system includes 4 first-level indicators and17 second-level indicators,and determines the weight of each level of indicators.The importance of the first-level indicators is: proximity location U4> new tunnel status U3>topography and geological conditions U1> existing tunnel status U2.4.Based on the AHP-cloud model,the safety risk of the existing Wutiao tunnel of the Pumei Railway was evaluated.The risk level of the existing tunnels K227 + 439 ～ K227 +515 is level IV,which is a very high security risk.K227 + 515 ～ K227 + 555 comprehensive rating risk level is level III,which is a high risk,and K227 + 555 ～ K227 + 600 comprehensive rating risk level is level II,which is a moderate risk.