Stability Analysis And Risk Assessment Of Surrounding Rock In Qingdao Metro Double Shield TBM Crossing Fault Fracture Zone

With the rapid development of domestic subway construction,the application of double-shield TBM in urban subways is becoming more and more extensive.During the construction process,due to the long interval mileage and complex geological conditions,sometimes it is unavoidable to cross bad geological sections.It is the main section where geological disasters and surrounding rock instability occur.When the double-shield TBM tunneling process encounters the fault fracture zone,construction safety problems such as the instability of the surrounding rock of the tunnel,the inrush of water and mud in the tunnel,and the excessive ground settlement are prone to occur.Therefore,it is of great significance to study the stability of the double shield TBM in the construction process of crossing the broken zone.Relying on the interval between Jiadingshan Road Station and Anshan Road Station of Qingdao Metro Line 8,this paper comprehensively uses theoretical analysis,numerical simulation and AHP-Fuzzy to analyze and evaluate the stability of double-shield TBM crossing the fault fracture zone.The specific research results as follows:（1）According to previous research and engineering experience,it is concluded that the risks of double-shield TBM crossing the fault fracture zone mainly include the risk of surrounding rock instability,tunnel water inrush and mud gushing risk,construction control risk and land subsidence risk.The risks that affect double-shield TBM The main factors of the excavation stability of the crushed zone are geological structural factors,hydrogeological factors,construction factors and time factors.（2）In this paper,FLAC3D software is used to establish the numerical models of faults with different degrees of deterioration and faults with different dip angles to analyze the influence of the double shield TBM on the stability of the fault breaking zone.The variation law of stress and plastic failure zone of surrounding rock.With the change of fault deterioration degree and dip angle,the maximum displacement of tunnel surrounding rock and its position change accordingly.Among them,the influence of fault width and fragmentation degree on the stability of double-shield TBM crossing the fractured zone has a certain synergy.The fracture degree of the fault mainly affects the size of the maximum shear stress and the damage degree of the surrounding rock,while the width of the fault affects the size of the damage area of the surrounding rock.When the dip angle of the fault changes,the maximum shear stress of the surrounding rock is always concentrated in the arch bottom area of the fault hanging wall,and the maximum shear stress reaches the maximum value at 60°and 120°respectively.The plastic damage area of the surrounding rock in the fault section is mainly concentrated in the tunnel.At the vault,vault bottom and vault waist,the maximum value of shear strain increment is obtained at the vault bottom of the hanging wall,and the larger the fault dip angle deviates from 90°,the greater the damage degree of the surrounding rock.（3）Based on the fuzzy comprehensive analytic hierarchy process（AHP-Fuzzy）,a stability evaluation model of the double-shield TBM crossing fault fractured zone is established.The membership matrix is finally obtained,and the stability evaluation matrix of the double-shield TBM crossing the fault fracture zone is obtained,and the stability level of the evaluation object can be determined according to the principle of maximum membership degree.（4）According to the engineering geological and hydrogeological conditions of the Jia-An interval,the fractured zone in the interval is analyzed,and the stability evaluation model established in this paper is used to evaluate the F_JA3 fault in the supporting interval,and the stability grade is obtained as grade III.The surface subsidence data,TBM slag output and TBM attitude demonstrate that the evaluation model is relatively close to the actual engineering situation;and from the four aspects of geological forecast,surrounding rock stability,driving attitude and driving parameters,it is proposed that the double-shield TBM crossing breakage is with construction control measures.