| With the development of railways,highways and urban subway tunnels in China,how to correctly evaluate the interaction between surrounding rock mass and supporting structures has become one of the important topics that affect tunnel construction safety and cost.The rock mass resistant coefficient is an important parameter to measure the deformation capacity of surrounding rock mass which limits the supporting structure.It reflects the ability of surrounding rock mass to bear load and has important influence on the calculation of lining internal force and deformation.So far,the research results of rock mass resistant coefficient mainly focus on the elastoplastic analysis of the homogeneous rock mass,and do not consider the brittle properties of rock and the anisotropy caused by joints in the rock mass.The rock mass resistant coefficient will be significantly affected by the brittle failure of rock and the anisotropy caused by joints,the value of which is uncertain.In the reliability design of the tunnel,the statistical characteristic of rock mass resistant coefficient is a necessary basic parameter.Therefore,it is an important and urgent task in tunnel design to analyze the elastic brittle plasticity,the anisotropy analysis of jointed rock mass and the analysis of statistical characteristics taking a as the center.Relying on the project of the National Natural Science Foundation of China,the calculation method and statistical characteristics of the rock mass resistant coefficient are studied in this paper.The calculation of rock mass resistant coefficient in elastic brittle plastic homogeneous rock mass,orthotropic layered rock mass,anisotropic conjugate jointed rock mass and fractured rock mass is systematically analyzed.Based on the statistics of a large number of field measured data,the statistical characteristics of rock mass resistant coefficient are obtained by Kolmogorov-Smirnov test.Combining with BQ rock mass classification,the optimized calculation method of rock mass resistant coefficient is obtained,and the recommended values of rock mass resistant coefficient under different qualitative characteristics of rock mass are given.The main research conclusions are as follows:(1)Based on the nonlinear unified strength theory and with the help of the maximum shear stress modulus,the elastic-brittle-plastic analytical solution of rock mass resistant coefficient is derived.The effects of intermediate principal stress,dilatancy,brittle plasticity,plastic zone parameters,Poisson's ratio and GSI can be taken into account.According to the parameter analysis,the rock mass resistant coefficient is significantly influenced by the intermediate principal stress,dilatancy and brittle plasticity,which increases with the GSI,elastic strains and Young's modulus in the plastic zone.Different criteria significantly affects when the plastic zone appears.The Mohr-Coulomb and Hoek-Brown criteria,as well as a series of nonlinear unified strength criteria between the two,are more suitable for analysing the rock mass resistant coefficient and self-bearing capacity than other criteria.Finally,this model is used to analyze the stress of the lining of the deep buried water diversion tunnel in Jinping ?Hydropower Station.(2)According to the mechanics theory of orthotropic material and the principle of stress variation,the calculation of the rock mass resistant coefficient for layered rock under two direction unequal stress is derived.According to the engineering example calculation,The rock mass rasistant coefficient exhibits obvious anisotropy and symmetry under different lateral pressure coefficients.The maximum value appears in the direction of ?/4,which is greatly influenced by the shear modulus of materials.With the increase of elastic modulus along one direction,the rock mass resistant coefficient increases,and perpendicular to this direction is almost unchanged.(3)Ten influencing factors including the elastic modulus of rock,Poisson's ratio and the properties of two sets joints were analyzed for evaluating the anisotropic distribution of rock mass resistant coefficient,by using orthogonal array testing strategy(OATS)and distinct element method(DEM),with Xinggongjie Station tunnel on No.2 Line of Dalian Metro as an example.And eighty-one computing models are established Measure the rock mass resistant coefficient by simulating radial hydraulic pillow.Using the variance analysis of OATS,the significant influencing factors at the level of five percent are the normal stiffness of the joints,the elastic modulus of the rock,the spacing of the joints and the intersection angle of two sets of joints.The rock Poisson's ratio has a certain influence on the rock mass resistant coefficient,and other has no significant influence.(4)The anisotropic distribution curves of rock mass resistant coefficient in the conjugate jointed rock mass are oval-shaped.The maximum value is along the direction of the two joints angle bisector,which is the long axis of the ellipse.With the increase of the ratio of tunnel diameter to joint spacing,the anisotropy coefficient increases first and then starts to drop,which converged to one when the ratio was equal to zero or infinite.Based on the above research,a theoretical calculation model of rock mass resistant coefficient in conjugate jointed rock mass is built,and calculation expression is derived.(5)For the calculation of rock mass resistant coefficient in fractured rock mass,based on the combination of Monte-Carlo and Matlab programming,a structure network model which can be used directly for UDEC calculation is generated.Eighty-one calculation models,which can consider the effects of rock elastic modulus,Poisson's ratio,joint density,joint dip,and joint trace length,are established by orthogonal test.A formula for calculating the rock mass resistant coefficient considering the anisotropy of fractured rock mass is obtained,which can reflect the influence of various factors and the anisotropic distribution characteristics.(6)In order to obtain the statistical characteristics of the rock mass resistant coefficient in homogeneous rock mass,stratified rock mass,conjugate jointed rock mass and fractured rock mass,the distribution type and statistical characteristics(mean,variance,variation coefficient,deviation,kurtosis,etc.)are obtained by using the Monte-Carlo method for 105 sampling.The statistical parameters of rock mass resistant coefficient in the stratified rock mass,conjugate jointed rock mass and fractured rock mass show obvious anisotropy.A lot of field measured datas have been collected.Using the statistical software SPSS to carry out the Kolmogorov-Smirnov test,the rock mass resistant coefficient obeys the normal distribution.The distribution function,the density function,the mean and the variance of rock mass resistant coefficient are further obtained.(7)Considering of the influence of rock uniaxial compressive strength,rock integrity and anisotropy,the function expression of rock mass resistant coefficient is constructed on the basis of the classification of BQ and the formula of Gallerkin calculation.The accuracy of the formula is verified by comparison with the suggested values given in the railway tunnel design code.Finally,combined with two rock classification indexes of uniaxial compressive strength and rock integrity,the recommended values of rock mass resistant coefficient under different qualitative characteristics of rock mass are given. |
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