| The stability of the tunnel is one of the most important problems in the tunnel engineering.At present,the design of the tunnel is still dominated by the engineering analogy method because of the theory behind the practice and the engineering geological conditions of uncertainty,which is a serious threat to the safety of construction personnel and equipment resulting from the vault surrounding rock collapse accidents.Therefore,it is a great significance in preventing tunnel collapse and improving the safety of tunnel construction to estimate the potential collapse surface and collapse range of the surrounding rock at the top of the tunnel according to the theoretical calculation,to clarify the fail ure mechanism of the bolt and to optimize the supporting structure.In the study of tunnel stability,the traditional theory is mainly Mohr-Coulomb strength theory and Hoek-Brown strength criterion,ignoring the influence of intermediate principal shear stress and belonging to single room strength theory.Besides,which is not suitable for rock failure in three direction stress state.In this paper,the shear failure of rock mass under triaxial stress is studied with the generalized nonlinear unified strength theory under plane strain,and then the stability of the tunnel and the failure mechanism of the bolt are studied based on the generalized nonlinear unified strength shear failure theory.The main contents and results are as follows:Firstly,in the limit equilibrium state,intermediate principal stress force between the maximum principal stress and minimum principal stress.On this condition,the paper introduced principal stress coefficient equation of plane strain,brought forward the shear failure of generalized nonlinear unified strength theory,analyzed the influence coefficient of intermediate principal shear stress and principal stress the middle and the influence on rock mass shear failure.The shear failure equation of generalized nonlinear unified strength theory includes not only the influence coefficient of intermediate principal shear stress and intermediate principal stress,but also the parameters reflecting material strength,brittleness and dilatancy,which has wider applicability.Secondly,on plane strain state,based on the shear failure theory of generalized nonlinear unified strength and the upper limit theorem of limit analysis,according to the failure characteristics and plastic theory of surrounding rock at the top of the tunnel,the two-dimensional curved collapse mechanism of tunnel top surrounding rock with arbitrary cross section in rock foundation is established,and the objective function including velocity discontinuous line equation is introduced,and then the equation is established by the equalization of the power of the external force and the dispersion rate of the internal energy consumption in the collapse mechanism.Using the variational method to calculate the extreme value of the objective function and obtaining the analytical solution of the collapse surface of the top wall rock of the tunnel with arbitrary section.Finally,taking the circular tunnel as an example,the influence of different parameters on the shape of the collapse surface of the top of the tunnel in the rock foundation is analyzed.Thirdly,based on the shear failure theory of generalized nonlinear unified strength of rock mass and the upper limit theorem of limit analysis,the slippage failure of anchor rod is studied under plane strain condition.Considering the shear ex pansion effect of Anchorage body and surrounding rock,it is deemed that the rock mass around the Anchorage section will inevitably produce lateral expansion deformation,and at the same time,without considering the weight of Anchorage body,The failure p attern satisfies the compatibility condition of deformation.The internal energy dissipation rate consists of two parts: the dissipation caused by the expansion and deformation of the rock mass around the Anchorage section and the dissipation on the thin deformation layer at the Anchorage interface.The external force work power is the ultimate pullout force work power.Based on the equal relation between them,the equation is established,and the variation law of the ultimate pull-out bearing capacity with grouting pressure of the anchor rod of different lengths is analyzed.Fourthly,based on the shear failure theory of generalized nonlinear unified strength of rock mass and the upper limit theorem of limit analysis,the whole failure of rock mass is studied under plane strain condition.Firstly,the failure mechanism of rock mass around the anchor rod under vertical load is established,and the objective function including the equation of discontinuous line of velocity is introduced.Then the function relationship is established according to the equal internal energy dissipation rate and external force work power in the failure mechanism.The extreme value of the objective function is obtained by using the variational method,and the analytical solution of the discontinuous velocity line equation and the width of the fracture surface are obtained during the whole failure of the anchor rod.Finally,taking the circular tunnel as an example,the influence of different rock mechanics parameters on the ultimate pull-out strength of the anchor is analyzed under the condition that the hole diameter of the anchor body is known. |
