Study On Nonlinear Constitutive Model Of Unfilled Structural Plane And Its Discrete Element Application

After a long period of geological structure,many discontinuous structural planes(faults,bedding and joints)will be formed in the rock mass,which will control the deformation and failure of the rock mass.With the increasing number of large rock mass projects such as mountain tunnels and slopes,the problem of engineering stability evaluation becomes more and more important.How to accurately evaluate rock mass deformation has also become an urgent problem to be solved in engineering.Combined with the research results of mechanical properties of structural planes,this paper selects an appropriate normal deformation model,establishes a new nonlinear shear model based on statistical damage mechanics and elastic-plastic mechanics,develops a nonlinear analysis method according to the characteristics of the constitutive model,compiles an embedded constitutive model in the secondary development environment of discrete element,and applies the constitutive model in practice,The research content is of great value for correctly evaluating rock mass deformation and promoting the development of nonlinear theory.The innovative achievements of the paper are as follows:1)Based on the operation mechanism of the constitutive model in UDEC,the applicability of Barton hyperbolic model in normal tension is analyzed in combination with the test results,and the nonlinear analysis and calculation method of the normal hyperbolic model of structural surface is established by using the method of iteration and increment.By changing the incremental step,the difference between the calculation results of the nonlinear method and the theoretical results is studied,the change characteristics of the relative error of the initial variables are analyzed,and the appropriate nonlinear calculation method is explored.2)The Barton type structural plane made of green sandstone was used for shear tests under different normal stresses.According to the test results,the characteristics of each stage of the shear curve of the structural plane are obtained,and the quantitative relationship between various mechanical parameters and the normal stress and roughness is established.At the same time,the different stages of the acoustic emission characteristics in the shear process are divided,and the relationship between the shear failure mode of the structural plane and the normal stress and roughness is obtained.3)Based on statistical damage mechanics and biological population growth retardation model,the evolution equation of structural plane shear damage is established,and then the constitutive model of structural plane shear damage is derived.The determination method of model parameters is given by control conditions and empirical formulas,and the physical meaning of model parameters is analyzed.The chaotic evolution characteristics of the constitutive model are studied by using the chaos theory,and the influence of different deformation increments on the constitutive model is obtained.The incremental analysis and calculation method of the damage constitutive model is established by using the Euler difference method.The empirical relationship between model parameters and structural plane characteristic parameters is established through a large number of statistical analysis.4)On the basis of elasto-plastic mechanics,an elasto-plastic incremental constitutive model under the condition of uncorrelated flow rule is established by using Barton shear strength criterion.Through optimization analysis,the functional relationship between post peak roughness JRC and shear plastic deformation is obtained,which is coupled with the shear elasto-plastic constitutive model,and an elasto-plastic incremental constitutive model that can reflect the nonlinear softening of post peak stress is established.The empirical relationship between model parameters and structural plane characteristic parameters is established by statistical analysis.5)Based on the implicit return mapping algorithm and the characteristics of structural plane constitutive model,an analysis and calculation method suitable for the elasticplastic incremental constitutive model of structural plane is developed.The accuracy and stability of the calculation are fully considered in the analysis and calculation method.The results obtained by the analysis and calculation method can reflect the non-linear change characteristics of shear stress at the structural plane and the non-linear change process of shear expansion.The numerical results are in good agreement with the experimental results.6)In the interface of the secondary development of discrete element software,the constitutive model is embedded into UDEC by using C++ language for secondary development.The embedded constitutive model can well reflect the nonlinear change characteristics of the structural plane under different stress states.In order to study the practicability of the embedded model,numerical simulations of multi group discontinuity compression,double discontinuity shear and different coupling discontinuity shear were carried out.In the compression results of multiple sets of discontinuities,the deformation of discontinuities will control the nonlinear deformation of rock mass;The combination and spacing of the roughness in the two discontinuities directly affect the shear strength and residual strength of the whole rock mass;The combination of roughness,the number of types and the combination order in the coupled discontinuity have a great impact on the overall mechanical properties of the discontinuity,and the stress distribution on the discontinuity will also be uneven.