Study On The Stability Of Tunnel Surrounding Rock With Weak Interlayer And Support Effect Analysis

The weak interlayer is the weak part of the surrounding rock of the tunnel,which restricts the deformation of the surrounding rock,the development and the yield failure of the surrounding rock,and has great influence on the stability of the surrounding rock.The physical and mechanical properties,distribution,thickness and combination of weak interlayer control the deformation,development and destruction of tunnel surrounding rock to a great extent.After excavation,the large deformation,failure and even collapse of the tunnel often appears in the weak interlayer and the surrounding area,which must be protected in the process of tunnel design and construction.So it is necessary to carry out a systematic and comprehensive study on the tunnel surrounding rock with weak interlayer.On the basis of previous research results,this paper studies and discusses several aspects,such as stability determination and evaluation of surrounding rock,simplified calculating model of tunnel surrounding rock with weak interlayer,the influence degree of weak interlayer on the surrounding rock of the tunnel,and the supporting effect.The main work and conclusions are as follows:(1)Selecting Mohr-Coulomb yield criterion as criterion to determine the instability of surrounding rock,adding the tensile strength to expand the criterion according to the Mohr-Coulomb model in FLAC3 D,dividing shear failure and tensile failure zone,defining the yield adjacent coefficient ? to evaluate the dangerous levels of surrounding rock,compared the area which ? is greater than 0.98 and the plastic zone of surrounding rock to verify the reliability of the index ?.The index can better evaluate the risk of unyielding rock mass,and to a certain extent,it also reflects the stability degree of the surrounding rock.(2)The structure composed of soft interlayer and surrounding rock is simplified as a composite beam structure model.Based on the relevant theory,the equations for calculating the boundary stress of soft interlayer are derived,and verified by FLAC3 D numerical calculation in a example.The results show that for the calculation of normal stress at the boundary of weak interlayer,it is feasible to simulate the interaction between soft interlayer and surrounding rock with composite beam structure model.After leaving the tunnel chamber boundary 1.5m,the error is small.(3)Through the numerical simulation calculation,it control the change of parameters such as weak interlayer dig angle,position,thickNess to study the influence law of displacement,Mises stress,the third principal stress,yield coefficient ? and the plastic zone of the surrounding tunnel rock.The results show that the dig angle of soft interlayer has great influence on the stability of surrounding rock when the dig angle is close to middle degree(30 degrees ~60 degrees).The influence of weak interlayer on the top of tunnel center is greater than the lower one.The closer it is to the excavation boundary line and the greater the thickNess of soft interlayer is,the greater the influence is.(4)Combined with the Ma Jia he tunnel project,simulating the construction and excavation process,considering the interaction between surrounding rock and supporting structure,it analyzed the supporting effect and compared the displacement data of caculation with the measured data of construction.The results showed that the spatial effect of the excavation of tunnel surrounding rock have influence on the distribution of displacement,stress,yield coefficient ? and the internal force of the supporting structure.The spatial effect is more obvious when closer to the working face and staying away from it has less impact.The weak interlayer increases the internal force of the supporting structure of the surrounding rock and itself,and make that internal force of the supporting structure of the left side is greater than that of the right side.