| The discontinuity is an intrinsic property of rock mass.The rock strength is usually much larger than the structural plane strength.Therefore,the mechanical properties of the structural plane mainly determine the mechanical properties of the fractured rock mass.Therefore,the fracture rock is studied using the hypothetical rock mass as the continuous medium.Studying the body will lead to excessive bias in the analysis results.The discontinuous deformation analysis(DDA)can reflect the discontinuity of rock mass deformation under the condition of satisfying the basic equation of elastic theory.It has the characteristics of large element displacement of discrete mass method and the rigor of finite element theory.It can well simulate and analyze the discontinuous deformation failure process of the block system.Based on the above unique advantages,discontinuous deformation analysis is widely used in the field of rock mass engineering.However,when the number of block contact pairs is large,the convergence and calculation stability of the opening and closing iterations are often not strong,and the corresponding contacts cannot be obtained quickly and accurately.State;secondly,when cohesion is considered,the cohesive force will be unreasonably removed under certain circumstances,which is conservative;in addition,there are still some problems in the numerical model selection in the multi-slip surface analysis of the block system.In this study,the discontinuous deformation analysis is taken as the basic structure,and the discontinuous deformation analysis method of the block system with the dynamic strength reduction of the structural plane is constructed.The research work of the following aspects is mainly carried out:(1)The DDA method is a numerical analysis method based on the principle of minimum potential energy.Solving the potential energy of the block system is the basis of the calculation of the DDA method.The displacement expression form of the potential energy function of the block system is derived.This form only contains the block displacement as the unknown.Based on the contact embedding judgment method,the normal and tangential embedding distances are derived,and the step function is used to simulate the corresponding block contact constraint state.Since the step function is inconvenient to directly perform numerical calculation,the hyperbolic tangent function is adopted.The form is smoothed out for calculation.On this basis,Lagrangian interpolation is introduced to obtain the expression of the general potential energy function under various contact states.On this basis,the potential energy function is solved by the variable scale method.By determining the basic iterative format,gradient,optimal step size and variable scale matrix,the displacement and contact state of the block system with corresponding time steps are obtained.Combined with the tunnel model,the calculation accuracy and calculation speed of the contact state explicit integration method are analyzed,and the robustness of the explicit integration method for the contact state of the block system is verified.(2)Through the classical example "single slider sliding model along the block",the accuracy of the parameter of the block structure surface cohesion in DDA is evaluated,and the reason for the inaccuracy of this parameter is explained.In DDA,a model in which the structural plane strength varies with the relative displacement between blocks(ie,the structural plane dynamic strength reduction model)is introduced.The strength reduction method proposed in this paper can automatically record the relative sliding displacement between the blocks(the relative sliding displacement between the blocks can be different,and the strength of each structural face can be reduced according to the increase of relative sliding displacement.The example shows that The improved structural surface dynamic strength reduction model can solve the problem of inaccurate simulation of cohesive force in the original DDA,and enables DDA to accurately analyze the critical stability of the system.(3)Study the stability of the slope of the Benxi line of Liaoning Province and the slope of the Fushun West open pit mine,obtain the structural surface appearance by means of unmanned aerial vehicle photogrammetry,and introduce the improved DDA program to realize the analysis model of the highway slope block system.Established and analyzed the discontinuous deformation of the block system to obtain the dangerous slip surface of the road slope and the recommended stripping surface.Through the analysis of the displacement monitoring data of the slope of Fushun West Open-pit Mine,the displacement zone of the slope block system is obtained,and the discontinuous deformation analysis of the block system is carried out.Based on the improved DDA method,the stability of the multi-slip surface of the northern slope of Fushun West Open-pit Mine is analyzed,and the most dangerous slip surface and secondary slip surface position are obtained. |
