Study Of Macro-micro Influence Of The Cross-sectional Shapes On The Mechanics Of Rock-like Materials

Rock mechanics and parameters obtained from laboratory experiments play an important role in rock engineering.Geometry of rock specimens may affect the results of experiments.As one of the geometry shape,the influence of cross-sectional shape on the rock mechanics and parameters has not been carefully examined.In order to investigate the influence of cross-sectional shapes on the mechanics of rock specimens under uniaxial compression state,a series of uniaxial compression test were carried out by coupling laboratory and simulated experiments.After obtaining the relative macroscopic parameters from lab,a comparison of macroscopic parameters and behaviors from simulated models and experimental specimens was carries out.Then the simulated models was verified and used to investigate the evolution of contact force chain and failure process of the rock specimens.The results show that:(1)Under the uniaxial compressive stress state,the influence of cross-sectional shapes on the constitute model and macroscopic parameters can be negligible.The results of the lab and simulation both show that the cross-sectional shapes have little influence on the stress-strain curves and macroscopic parameters.(2)There are different influences of cross-sectional shapes on the microscopic structures on the different stages of the uniaxial compression test.Before the peak stress,the influence of different cross-sectional shapes on the microscopic structures of specimens is very small.After the peak stress,the cross-sectional shapes do have an influence on them.Before reaching the peak stress,all specimens did not show many obvious differences in the distributions and evolutions of strong contact force chain network,strong contact density and contact force.Particle rotation,displacement and contact damage of all specimens are similar.After that,in radial direction,specimens with circle cross-sectional shape have the least range of change of strong contact density while the pentagon ones have the largest.The curves of contact force after peak strength are different.(3)Under the uniaxial compression stress state,the evolutions of the specimens with different cross-sectional shapes are different.Before peak stress,the boundary work mainly converted into parallel bond strain energy and strain energy.Only less energy is dissipated.At the same time,the energy curves of all specimens is nearly identical,indicating that cross-sectional shapes have a very small influence on energy before the peak stress.After that,due to the increasing broken bond and relative moment between the particles,parallel bond strain energy and strain energy were decreasing and slip energy and local damp energy were increasing.Energy curves of specimens with different cross-sectional shape began to divert and show appreciable differences,indicating that cross-sectional shapes did have an influence on energy evolution of specimens.(4)DEM models can simulate macroscopic behaviors of specimens with different cross-sectional shapes under uniaxial compressive stress state.In the simulation,the calibrated microscopic parameters of cylinder specimens were passed into other specimens and then they were all under uniaxial compression tests.The simulated macroscopic parameters showed a good agreement with the experimental ones.(5)DEM model can investigate the failure mechanics of specimens with different cross-sectional shapes in particle scales,which provide a new method to investigate failure behaviors.In this research,particle rotation,displacement and contact damage are used to analyze the whole failure process and mode of the specimens.Particle rotation can clearly show the fracture zone.Particle displacement can help analyze the reason for specimens failure and contact damage can reveal the spatial damage distribution of specimens during the whole loading process,and better clarify the relationship between particle rotation and displacement.