Rail Transit Tunnel Construction Risk Assessment Research Considering Complex Geological Conditions

The rail transit tunnel construction in mountainous city faces many risks, includingtunnel landslide, water inflow, rock burst, collapse of nearby buildings, etc., caused byits complicated and volatile geological environment. Once the accident occurs, it willdamage the construction machinery and will cause the enormous economic losses to beeven great casualties.The thesis researches various adverse geological phenomenon which encounteredin the mountain city rail transit tunnel construction process and caused inclination andeven collapse of nearby building by tunneling process, and analyzes mainly themechanism of accident caused by geological disasters under unfavorable geologicalcondition and their impact factors. Establish a rail transit tunnel construction riskassessment model, considering complex geological conditions, using the theory ofFuzzy-Analytical Hierarchy Process. Main research contents are as follows:①Compared different methods of risk assessment, this thesis elects the method ofFuzzy-Analytical Hierarchy Process comprehensive assessment, and concludes thebasic steps of the evaluation method.②Selected common disaster collapses, gushing water, gas, rock burst, surfacebuildings settlement deformation as five-level indexes of risk, and the corresponding23secondary indexes. Build a system table of mining method rail transit tunnelconstruction risk factor index. The index system table can be adjusted according to thevariety of tunnel types and construction environments.③A comprehensive evaluation model of rail transit tunnel construction risk undercomplicated geological conditions is established, by introducing the principles of fuzzymathematics and analytic hierarchy process and by using fuzzy hierarchycomprehensive evaluation method. The loss probability and consequences of tunnelconstruction was evaluated through the fuzzy comprehensive evaluation model. Theevaluation model can be adjusted according to different geological conditions or thedifferent risk factor index, with some versatility.④Using the fuzzy-hierarchy integrate evaluation model, the construction riskassessment of Zhongliangshan tunnel located at Chonqing rail transit Line No.1(ShaPingBa~University twon) is performed. The overall construction risk grade ofzhongliangshan tunnel is evaluated as category IV (high risk); In special risk assessment, the level of collapse risk is evaluated as low, that of the gushing water risk as high andthe gas risk as low, rock burst risk as moderate and surface subsidence risk as moderate.As a result, in Specific risk assessment, the comprehensive evaluation risk grade is high.Nine tunnel faces have appeared water burst, the maximum inflow of single holeexceeds5,000cubic meters a day, pressure around2.2MPa during construction. Itdescribes the proposed fuzzy evaluation model is accurate in a certain degree and playsan important role in the application of practical risk assessment of rail transit tunnel.