Theoretical And Experimental Study On The Evolution Of Mechanical Properties Of Non-viscous Granular Materials Under Dynamic Loading

With the development of construction and transportation industry,the scale of urban construction in our country is getting bigger and bigger.Due to the widespread distribution of sand in our country,more and more buildings and rail transit are built on sandy foundations.In recent years,large-scale liquefaction of sandy soil caused by seismic activity has caused huge economic losses.Therefore,the dynamic characteristics of granular materials,represented by sandy soil,have become a hot topic in geotechnical engineering.As a typical granular material,the mechanical characteristics of sand are very complex.The mechanical properties of sand under different stress conditions are very different,which can be divided into small strain,plastic deformation and liquefaction large deformation in different deformation scales.At present,the research on the mechanical properties of granular materials generally adopts the indoor tests to explore the mechanical properties of granular materials based on experimental phenomena,but the experimental phenomena can’t reflect the micro mechanism of the mechanical behavior of granular materials,and the experimental research based on this with great uncertainty.Firstly,this paper summarizes and analyzes the research progress of dynamic characteristics and experimental analysis of granular materials at home and abroad,and points out the shortcomings of existing research.Based on this,from the micro point of view,the micro mechanism of mechanical characteristics of granular materials is studied by combining experimental and numerical simulation analysis:(1)From the microscopic point of view of particle contact,the energy unit produced by particle-particle contact is regarded as an energy state.Through theoretical analysis,it is determined that the distribution of energy states in the granular material conforms to the Maxwell distribution model.On this basis,the failure conditions of particle contact are defined,and the softening model of the granular material under external dynamic load is obtained.Based on this,the creep model is introduced to obtain the fluidized deformation constitutive of the material under cyclic dynamic load.(2)With the introduction of state parameters,based on the thermodynamic theory that the system always tends to be stable under natural conditions,ignoring the influence of objective factors,the evolution state of the system’s modulus under ideal conditions is qualitatively analyzed,and the time evolution model of the particle material’s modulus in the decay and recovery process is obtained.(3)Based on the theoretical model proposed in(1)and(2),a large number of laboratory tests were carried out using resonant column and GDS hollow torsional shear apparatus(SSHCA),during this,important laboratory test results were obtained,including the softening of the modulus under dynamic response,the evolution of the modulus under different stress states,and the fluidized deformation under dynamic load.Fitting obtains important parameters α,β,,η,a,r,D,deeply discusses the change law and the relationship between the parameters,finally compares,analyzes,discusses and summarizes the theoretical model predictions and test results.(4)Combined with the PFC3 D discrete element software,the stress of the particle material in the test was simulated,and the distribution of the microscopic contact and the fluidized deformation of the particle material under the action of dynamic load were derived.The contact state of the particle and the contact change of the particle under the action of external load were simulated and verified with the laboratory test results.