Study On Stress Characteristics And Surrounding Rock Deformation Law Of Supporting Strucyure Of Tunnels With Different Forms Of Weak Interlayer

As a geological body under natural stress,the biggest difference between rock mass and general artificial materials is that it has structural plane and discontinuity.Under the influence of long-term geological movement and external environment,weak layers(including weak structural planes,dikes,faults,etc.)whose strength and stiffness parameters are lower than those of the surrounding rock mass will be formed.Most of these weak layers are layered or banded in space,and have a certain thickness.From the point of view of engineering mechanics,the existence of weak layer will inevitably lead to the change of stress and strain state of engineering rock and soil.With the rapid development of traffic infrastructure construction and the rapid development of mountain expressways,mountain tunnels will inevitably pass through weak layers of different forms(occurrence and thickness)in the process of design and construction.Due to the poor mechanical properties of the weak layer,the convergence deformation after tunnel excavation in this kind of stratum is often difficult to control,which increases the difficulty of tunnel construction and structural design.On the other hand,there is still a lack of systematic research on the influence of the inclination,tendency and thickness of the weak layer on the deformation of surrounding rock and the force of support after tunnel excavation.In view of the above problems,this paper first uses the similarity theory to configure the test materials that match the mechanical parameters of the actual engineering rock mass.combined with the physical model test,the deformation law of tunnel vault and arch waist and the stress characteristics of initial support under the condition of weak layer inclination are studied,and the results are compared with the results of numerical analysis.Secondly,the numerical analysis method is used to further study the influence of inclination and thickness on surrounding rock deformation and support force.finally,sensitivity analysis is made for three kinds of morphological parameters.The main conclusions of this paper are as follows:⑴ The model test of the weak layer tunnel with different inclination angle is carried out,and the results show that changing the inclination angle of the weak layer has a significant influence on the surrounding rock stress and the supporting structure of the tunnel.With the increase of the dip angle of the weak layer(45°,60°,90°,120°,135°respectively),the surrounding rock displacement,the contact pressure between the surrounding rock and the initial support and the internal force of the initial support first decrease and then increase.The maximum values of dip angle of weak layer,contact pressure of surrounding rock and bending moment of initial support all appear at the arch foot,and the maximum axial force is at the arch waist.⑵ Corresponding to the working conditions of the model test,a threedimensional numerical model with different inclination angles of the weak layer is established,and the results of numerical simulation and model test are compared comprehensively.For the displacement of vault and arch waist,it is found that the results of numerical simulation and model test are consistent in law,but there is a difference in numerical value.Through normalization treatment,it is found that the final displacement values of vault and waist with different inclination angles are similar between numerical simulation and model test.With the increase of the inclination angle of the weak layer,the contact pressure between the surrounding rock and the initial support and the internal force of the initial support decrease at first and then increase with the increase of the inclination angle of the weak layer.Under the different working conditions of the inclination angle of the weak layer,the surrounding rock pressure and the bending moment of the initial support are the highest at the arch foot,and the axial force of the initial support is the largest at the arch waist.⑶ A three-dimensional numerical model with different weak layer tendency is established to explore the influence of the change of weak layer tendency on the deformation of surrounding rock and the stress of initial support.The results show that the change of the tendency of weak layer has little influence on the deformation and contact pressure of surrounding rock.For the initial supporting structure,the bending moment of the arch foot varies greatly with the tendency of the weak layer,the axial force decreases when the tendency of the weak layer changes from 30°to 60°,and increases when the tendency of the weak layer changes from 120°to 150°.⑷ Furthermore,three-dimensional numerical models with different thickness of weak layer are established,and it is found that when the dip angle of weak layer is constant,with the increase of thickness of weak layer,the contact pressure of surrounding rock increases and the deformation of surrounding rock increases accordingly.For the weak layer with different thickness,the maximum bending moment of the initial support appears at the arch foot,and the maximum axial force appears at the arch waist.With the increase of the thickness of the weak layer,the bending moment and axial force of the initial support increase accordingly.⑸ The sensitivity of three kinds of morphological parameters of weak layer was analyzed.Based on the sensitivity analysis method,the relationship between the sensitivity of three kinds of weak layer morphological parameters to surrounding rock deformation,surrounding rock pressure and initial supporting structure is obtained.it is found that the change of the thickness of weak layer has the highest influence on surrounding rock deformation,surrounding rock pressure and initial supporting structure.The results of sensitivity analysis have certain guiding significance for the safe construction of tunnel across weak layer.