Study On Macroscopic And Microscopic Mechanical Properties Of Granular Materials Based On Rate-state Friction Model

The study of granular materials has a wide range of applications in industry and rock and soil,and its scope of influence involves civil engineering,agriculture,chemical industry and other industries.Taking geotechnical engineering as an example,the shear failure of sandy soil foundation,pile bearing capacity,weak fault displacement and slope stability are all related to soil particles.Therefore,in order to avoid the huge economic and personnel losses caused by these engineering problems,it is necessary to focus on the study of particle force mechanism,and the development of accurate particle material strength theory is the basis and key to its safe application.Study the mechanical properties of granular material,many scholars mainly adopts the physical test,numerical simulation and the method of constitutive model,the constitutive model method is based on microscopic observation and experiment mechanics to establish the corresponding mechanical model,the macroscopic mechanical quantity and micro mechanics,and quantitatively analyze the mechanical behavior of particles body.In this paper,considering the influence of the contact behavior between particles on the overall mechanical behavior of the particle system,and combining with the rate-state friction model,a practical constitutive model is proposed and the internal mechanism of the mechanical behavior of granular materials is explained.The specific research work is as follows:(1)Based on the rate-state friction model(RSF),the relationship between the microscopic mechanical quantity and the macroscopic mechanical behavior of the granular system was established,and the theoretical model of the macroscopic strength evolution of the granular material was established based on the energy balance equation.Compared with the results of direct shear test,it is found that the model is in good agreement with the test,which indicates the applicability and accuracy of the shear strength model for granular materials.Then the model parameters were fitted to obtain the relationship between each RSF parameter and vertical load.(2)Based on the rate-state friction model,the stick-slip phenomenon of granular materials was studied theoretically,and the mechanism and influencing factors behind stick-slip instability of granular faults were explored.RSF parameters were obtained by strength step test and instability criterion was introduced to define and judge the conditions of stick-slip instability.The research results again verified the key factors leading to stick-slip:k_c must be small enough to not exceed the fault stiffness k,that is,to ensure that the stiffness ratioKis close to 1.Meanwhile,the stiffness ratio can be used to find the relationship between it and the size and period of particle slip.(3)Explores the granular materials under the stress path of a more simple and a larger range of shear rate under shear,and compare the results with the theoretical predictions,to verify the proposed model of shear strength under the condition of different shear applicability,GDS hollow cylindrical torsional shear test of granular materials under the action of pure shear strength evolution behavior was studied,The experimental results show that the strength evolution of granular materials under pure shear is close to that under direct shear,and the effects of shear rate and confining pressure on the strength and deformation of granular materials are analyzed.