Simulation Of Dynamic Rock Failure By Discontinuous Deformation Analysis

With sustainable exploitation of energy,engineering construction is becoming increasingly difficult.Development of rock mechanics is facing more and more new challenges.Because rock contains many discontinuous surfaces,like mineral interfaces,joints and faults.It has strong heterogeneity,which makes it complicated to study mechanical properties by theoretical or experimental methods solely.With the development of computer technology and numerical methods,numerical simulation has been widely used in rock mechanics and engineering.Discontinuous Deformation Analysis(DDA),as an implicit discrete element method,is widely used to solve discontinuous problems at an engineering scale.However,there are few systematic studies on DDA parameter sensitivity analysis for material failure at the laboratory scale.Thus,it is difficult to conduct quantitative analysis,and the simulation of dynamic rock failure is preliminary.To solve this problem,the pre-processing programs and the strategy of improvement for disk-based DDA and block-based DDA are developed.The calibration methods,which are suitable for quantitatively studying the static and dynamic mechanical properties of rock,are established and proposed.To this end,the dynamic compression test with split Hopkinson pressure bar(SHPB),dynamic Brazilian test with SHPB and the dynamic crack propagation tests are quantitatively studied by DDA.The main contents of this paper are as follows:(1)Two particle packing algorithms are proposed.The algorithms are based on a triangular mesh to fill the elements and vertices.The new disks are obtained by solving equations according to the contact relationship of adjacent disks.The algorithms have advantages of strong applicability and high efficiency,and are the basis of modeling of disk-based DDA.(2)A new BPM,consisted of a normal,a shear and a rolling spring,is proposed for disk-based DDA.The BPM can resist the relative rotation between disks.Several dynamic and static rock mechanical tests are simulated by disk-based DDA.As a result,The BPM can obtain a reasonable compression-tensile ratio and simulate rock failure well.(3)DDA using Voronoi discretization is established.The effects of different discrete forms(triangle,Voronoi polygon)and different degrees of discretization on the results are compared.The results show that regular discretization will lead to unreasonable failure,so a proper degree of randomness is necessary.The Voronoi model leads to great computational efficiency,a realistic compression-tensile ratio,and is suitable for simulation of rock failure.(4)Parameter sensitivity analyses are carried out for disk-based DDA and block-based DDA,respectively.On this basis,the calibration methods were proposed,and the advantages and disadvantages of disk-based DDA and block-based DDA in simulating rock failure are compared and analyzed.Since DDA using Voronoi discretization has advantages in mesostructure,calibration,mesh-dependence,and calculation results.This method is adopted in the subsequent simulation of dynamic rock failure.(5)Dynamic compression test,dynamic Brazilian test,and the dynamic crack propagation of brittle materials are simulated by DDA using Voronoi discretization,which is consistent with the experimental results.