Mechanical Response Analysis Of Tunnel Excavation In Fractured Area

With the continuous construction of high-grade railway and highway projects in western mountainous areas,more and more deep-buried tunnels are crossing complex fault zones or even active faults.In these complex conditions,large deformation and destruction of structural arch,floor uplift,initial support failure and secondary lining cracking often occur after excavation,which seriously affects the safety and stability of tunnels.Therefore,the engineering mechanics characteristics of tunnel fault fractured zone and its mechanical response characteristics in the process of tunnel excavation are one of the important engineering problems that need to be solved urgently in the construction of high-grade traffic in western mountainous areas.In view of the actual needs of the project,this paper mainly studies the mechanical response analysis of tunnel excavation in fault-fractured area,and combines the macro-regional fault stability with the mechanical response of local tunnel surrounding rock.Firstly,according to the formation,classification and theory of faults,the macro-judgment method for judging the stability of faults is selected.Based on the measured in-situ stress data of several fault zones and combined with the classical Coulomb sliding friction criterion,the active background and macro-stability of regional shallow structures are analyzed.The results show that when judging the stability of faults,the slope method is applied to the limited data of multiple regions.The identification of points is not intuitive,and it has its superiority in macro-discrimination of a large number of groups of in-situ stress data;"parallel boundary method" is more applicable to the discrimination of limited groups of in-situ stress data in many areas,and the location and scope of the fault risk zone can be quickly detected by serial number.Then,combined with a deep-buried tunnel project crossing the gentle dip stratum of the fault zone,mechanical parameters of rock are obtained through laboratory mechanical tests,and a tunnel excavation design model without fault is established and calculated.The rationality of the calculation model is verified by comparing the calculation results with the actual test results of the project.By adding fault contact element to the above calculation model,the stress characteristics,deformation displacement and plastic yield characteristics of tunnel surrounding rock under the condition of tunnel section with or without fracture zone are calculated and compared,and the influence of fault on the mechanical state and safety of tunnel excavation is analyzed.Furthermore,from the point of view of plastic yield,displacement field and stress field distribution,the influence of fault location,fault dip,fault thickness and fault modulus on tunnel excavation process is studied by model calculation.The results show that when the fault intersects with the tunnel,the depth of the plastic yield zone at the intersection increases greatly,but the depth of the plastic zone in the fault zone decreases.The location of faults has the greatest influence on the displacement of the tunnel wall which intersects or is nearest to them,but far away and has little influence.The location of horizontal faults or whether there are faults has little influence on the principal stress value at the bottom of the tunnel wall,but has some influence on other tunnel positions.Faults with vertical dip angle have the greatest influence on tunnel wall,which is manifested by elongating the distribution of plastic zone and increasing displacement of surrounding rock in intersecting zone.The thicker the fault,the greater the total displacement at the same depth,the deeper the depth,and the smaller the difference.When the elastic modulus of the fault is small,the yield zone in the fault zone is obviously smaller than that around the fault zone,and the difference between them is large.With the increase of the elastic modulus,the difference between the two gradually decreases until it disappears.When the modulus of the fault is very small,the displacement at the intersection of the fault and the tunnel wall is very large.With the increase of the modulus,the displacement decreases rapidly,showing a power function change trend.The research methods and conclusions of this paper can be used for reference for the follow-up research in this field,and can also provide some basis for the site selection and design of the above-mentioned tunnel crossing the fault fractured area.Figure 39 table 6 references 69...