Stability Analysis Of Tunnels In Layered Phyllite Stratum

Among the three categories of rocks which are widely distributed in nature,most of the sedimentary rocks and metamorphic rocks are characterized by feature of anisotropy.The physical features,structural properties and stress-strain relations of anisotropic rocks are related to the weak planes.With the development of tunnels in China,the anisotropy of rocks has a great influence on the stability of surrounding rock and the safety of lining structure.Therefore,it is necessary to carry out an in-depth study on this issue.In this paper,taking the partridge tunnel of Wenma Expressway as an engineering background,the macro-anisotropic and meso-anisotropic characteristics of phyllite is studied by means of laboratory experiment,numerical simulation and theoretical analysis.Furthermore,the safety analysis model of lining structure considering structural deterioration and rheological effect of surrounding rock is established.The main achievements are displayed as follows:(1)The macroscopic failure characteristics of specimen is obtained by triaxial compression test,Brazil split test and uniaxial compression rheological test.During the experiment,the failure evolution process of specimen is explored from a mesoscopic perspective by means of acoustic emission,high-speed photography and other test methods.Meanwhile,the mesoscopic failure mechanism of specimen is revealed through scanning electron microscopy and 3D laser scanning.(2)Based on the discrete element method,a numerical approach is established to reflect the tensile and compressive anisotropy of rocks.Furthermore,a burgers damage model is put forward to obtain a rheological model which can characterize anisotropic and accelerated rheological features of rocks.(3)Based on theoretical deduction,an elasto-plastic solution of transversely isotropic buried tunnel under point-anchor action is obtained,and the effect of anisotropy parameters on deformation of surrounding rock is analyzed.In view of the limitation of this theoretical derivation,the mechanical response of surrounding rock after tunnel excavation under different inclination and dip angle is studied using numerical simulation.(4)Based on finite difference theory,a nonlinear rheological element and an anisotropic constitutive model are introduced into an element-combination model.Thus,a nonlinear viscoelastoplastic rheological constitutive model describing rock anisotropy is proposed.(5)Based on corrosion theory,a corrosion mechanical model of anchor bar and rigid frame are deduced and embedded into the existing calculation model through secondary development.Meanwhile,structural safety of secondary lining with pre-existing cracks is analyzed based on shell-joint calculation model,and the effectiveness of this model is verified by field test.On this basis,a safety analysis model for lining structure considering structural deterioration and rheological effect of surrounding rock is established.The relationship between safety factor at different positions of tunnel and dip angle is studied,and the influence of cracked degree of secondary lining on structural safety is also explored.