Study On The Influence Mechanism Of Parallel Bond Model Meso Parameters On Macro Parameters And Destruction Mechanisation

In the process of PFC simulation of rock engineering,how to select micro parameters quickly and accurately is extremely critical.At present,most of the existing research achievements are directed at non-viscous materials.Therefore,in this thesis,based on the PB Model which is widely used in the discrete element,i.e.Parallel Bonded Contact Model,the control variable method is adopted to comprehensively analyze seven more important micro Parameters and confining pressure,to study their influence laws on macro mechanical parameters,and to obtain the relevant influence relations.The failure mode,particle displacement and force chain development law of the specimens are analyzed.The influence on the evolution of micro-fabric is analyzed.The main conclusions are as follows:(1)The main influencing factors of elastic modulus are:parallel bonding modulus,particle friction coefficient,tangential bonding strength,parallel bonding stiffness ratio and particle contact modulus.The main influencing factors of Poisson ratio are:parallel bond modulus,particle friction coefficient,particle stiffness ratio and parallel bond stiffness ratio.The main influencing factors of cohesion are particle friction coefficient,normal bonding strength,tangential bonding strength and parallel bonding stiffness ratio.The main influencing factors of friction angle are friction coefficient and tangential bonding strength.(2)Separation occurs when the tensile force between particles is greater than the bonding strength,resulting in relative displacement.Scratched zones will appear on the macro level and force chain will break at the area of the scratched zones.The normal bond strength between particles characterizes the tensile limit between particles and the tangential bond strength characterizes the shear limit between particles.When the normal bond strength is significantly greater than the tangential bond strength,the specimens show the form of single-split surface and vice versa.The particle contact modulus has a great influence on the failure mode of the specimens.With the increase of the particle contact modulus,the failure of the specimens changes from single-cracking surface to double-cracking surface.The peak strength increases with increasing normal and tangential bonding strength.As the ratio of parallel bond stiffness increases,the peak strength of the specimen decreases.(3)The transverse(-30°～ 30°,150°～ 210°)particle coordination number decreases and the vertical(-60°～ 120°,150°～ 210°)particle coordination number increases after the destruction of the biaxial test specimen.The larger the parallel bond modulus,the smaller the strain inflection point of the sample body,which indicates that the earlier the sample appears shear dilation,the properties of strain-softening materials like dense sand or super-consolidated clay,and the parallel bond stiffness ratio and particle contact modulus will have similar effects on the sample.The larger the normal bonding strength,the smaller the volume strain inflection point,which indicates that the later the sample is sheared,the properties of strain-hardening materials like loose sand or normally bonded clays.Finally,some conclusions of this thesis are qualitatively checked by the indoor triaxial test data of Liu Yichen.The micro parameters of the test were calibrated and it was found that the failure modes,such as the cracking surface form of the indoor triaxial test,were in good agreement with the numerical test results.