Approximate Gradation Condition Study On The Differences Of Mechanical Properties Of Sand And A PFC Analysis Method

In general,the rock mass material is composed of a large number of granular materials,the sand in the formation process due to the decomposition of organic matter and mineral composition,resulting in high porosity of sand,particle evacuation and anisotropic structure characteristics.So far,in order to better understand the characteristics of this geotechnical material,many scholars have devoted to the study of the mechanical properties of sand.Although some achievements have been made on the macroscopic characteristics of sand,the research of sand is still scarce.In this paper,the mechanical properties of sand are analyzed considering the micro-macro characteristics of sand,in order to explain the purpose of macroscopic phenomena from the Meso.In order to achieve this goal,this paper proposed the method of PFC grain flow simulation and laboratory test,first the indoor test of different particle gradation sand?CC,Cu,particle size distribution?,and then the PFC simulation experiment,the results are compared to explain some macro phenomena from the Meso.And through the PFC simulation instead of the reliability of indoor direct shear test,the relationship between the gradation and shear strength is obtained.And the existing particle size division depends on the screening experiment,and is limited by the sieve pore size,through the PFC particle flow fitting experiment can be experimental particle size distribution of random.In this way,the d₅₀ classification can be classified according to the sand classification criteria,and further through the grain grading parameters of the uneven coefficient to define the internal friction angle of sand can provide a valid reference value for the internal friction angle.The main achievements of this paper are as follows:1.It is found that when d₅₀ and d₁₀ are constant,the internal friction angle increases with the increase of the non-uniformity coefficient Cu,and when the Cu is larger than When the d₅₀ and Cu are constant,the internal friction angle increases with the increase of d₁₀.When the value of d₅₀ is changed,the internal friction angle is found.When the value of d₅₀ is constant,The effect is far less than the impact of Cu on the internal friction angle.2.The results show that the size of the shear strength is the same as that of the graded shear,and the shear strength is bigger.In addition,according to the direct sand of uniform sand experiments show that the sand contains more coarse particles,the higher the shear strength of sand.3.Neural network training through Matlab,and enter the macro parameters to complete the selection of PFC2 D mesoscopic parameters.4.Using PFC2 D to simulate the indoor direct shear test of sand,the porosity,coordination number and contact force between sand particles and particles are more intuitively seen by the output of the figure.And demonstrate the consistency of the particle flow simulation method and the laboratory test,and can simulate the indoor test by the particle flow.5.The porosity and coordination number of the porosity and coordination number of the circle measured at the middle and four corners of the shear box are analyzed.As the shear continues,the porosity and the coordination number are a process of continuous change.And the change of porosity and coordination number at different positions is different.The porosity of the upper left corner and the lower right corner of the initial stage is the smallest,and the average number of coordination is the highest,which is consistent with the actual distribution of force in the shear process.In the later period of shear,the particles in the shear zone move,rotate and roll more obviously due to the shear action,so the average coordination number of the two corners drops rapidly and increases with the porosity.6.Using PFC2 D,to achieve the classification of the arbitrary,can be obtained under different refinement under the shear strength and internal friction angle,as an effective reference value for the project.