Study On The Way To Ensure Coarse Grained Soil Microcosmic Index By PFC

PFC3D is a kind of particle discrete element method based on the method of discrete element to simulate the movement and interaction of rigid sphere,which is widely used in geotechnical engineering at present.In the process of fitting,the rationality and accuracy of the micro parameter value are directly related to the simulation effect and the current test and testing technology can not get its micro parameters.To take limestone gravelly soil as the research object,to borrow PFC3 D as the research tool,and to take the test method as the means,starting from the definition of micro parameters in PFC,I design a direct shear test which can obtain micro parameters directly.The shear of single particle group and double particle group is designed from the test particle group,and it is designed from the surface morphology(the particle size is 40～60mm,20～40mm,10～20mm,5～10mm).Using the response surface method as a mathematical tool,and taking macro parameters and micro parameters as the research data object,the inversion of micro parameters is carried out,and the characteristics of the inverse calculation method and the forward calculation method are compared.The main conclusions of this paper are as follows:(1)The shear test is a method to obtain the micro parameters directly.It abandons the chance and uncertainty of the traditional way "trial and error method",and it can explain the meaning of the micro parameters more from the micro point of view than some methods that use mathematical tools to get the micro parameters;(2)In the linear contact model,the normal stiffness indicates the ability to resist normal deformation between two particles in contact;the tangential stiffness indicates the ability to resist tangential deformation between two particles in contact;the friction coefficient μ indicates the ability to resist relative movement between two particles in contact;The shear test imitate the stress state of particles in the whole sample.From the shear test,the material,size,shape and contact mode of the two particles in contact with each other determine the micro parameters of particles,which are shown as follows: the larger the average value of the stiffness of the two particles in contact with each other,the greater the contact stiffness of particles;the friction between particles depends on the two particles whose contact surface of the particle itself is more smoth,and the size and shape of the contact surface of the particle itself affect the friction properties of the particle itself.(3)The basic element of the study is to evaluate the microscopic parameters of the macro sample,which reflects that the microscopic parameters reflect the whole macro sample.Through the property command,we would get a parameter that can reflect the whole sample,and the macro data,such as sample size,grading,etc.,determine the final parameter value.The specific reflection is as follows: the proportion of contact formed by any particle group in the grade proportioning affects the micro parameter value of the whole macro sample according to the proportion(4)Different from response surface method,which takes the data as the research object,the inversion method of finding the relationship between macro response and micro parameters is different;shear test method is based on the shear test to obtain the micro parameters between particles,and the specific sample grading,according to the weighted average method to obtain the micro parameters of the overall sample;this method starts from the definition of micro parameters of particles,and from the overall macro parameters The method of fitting is not used to get the final micro parameters.