Numerical Study On Macro And Micro Characteristics Of Construction Waste Based On Discrete Element Method

With the advancement of China’s urbanization process,a large number of buildings,structures,traffic lines are being updated.With the upgrading of various facilities,a large amount of construction waste will be generated.If a large amount of construction waste can be reasonably recycled and applied,it is of great significance to the ecological construction and land resource protection in China.Since construction waste still has large particle size after crushing,and the laboratory test of large particle size requires relatively high instrument size,this paper attempts to use discrete element method to conduct a series of studies on the macro and micro mechanical properties of construction waste,so as to provide reference for large-scale recycling of construction waste.The research contents are as follows:(1)Establishment of particle flow model of construction waste with real shape:this study proposes a convenient method to establish three-dimensional model of real shape.First,the 3D contour map of real particles was obtained by 3D modeling software.The contour was filled with PFC3 D to obtain particle clusters(clump).The experimental simulation was established by PFC3 D and the particle clusters were evenly distributed according to the statistical grading.According to the above method,a uniform granular flow model of construction waste can be obtained.(2)Large-scale direct shear test and numerical simulation study on construction waste: First,heavy compaction test and determination of moisture content by alcohol combustion method were carried out on the screened construction waste to ensure the stability of samples of each group in the process of construction waste test.Then the shear strength parameters of construction waste mixtures with different contents were measured through large direct shear tests.Then PFC3 D is used to simulate the direct shear test of construction waste mixture under the same test conditions.Finally,by adjusting the material parameters of the simulation test,the simulation results are close to those of the laboratory direct shear test.The final results show that the simulation analysis can well simulate the laboratory test.In the shear process of construction waste,the shear hardening first reaches the peak and then the softening phenomenon appears,and in the high confining pressure shear test process,the construction waste particle breakage phenomenon appears.(3)Study on microscopic shear characteristics of construction waste: the changes of microscopic mechanical parameters such as shear band,contact network,probability density and anisotropy in the direct shear test of construction waste mixture were analyzed,and the relationship between microscopic and macroscopic phenomena was studied.The results show that the contact network of construction waste mixtures with different contents changes,which is reflected in the change of contact force,direction and anisotropy parameters in the force chain.These microscopic parameter changes explain the shear strength change of construction waste mixtures.(4)Construction waste triaxial compression test simulation study: the triaxial compression test model used the real particle model,and the model data referred to the calibration parameters of construction waste direct shear test.In terms of data monitoring,in addition to monitoring a series of data in the direct shear test,data monitoring of sliding contact,strong and weak contact and different types of contact are added to further analyze the construction waste.In general,the discrete element method can well simulate the micro-mechanical activities of construction waste under the action of force,and the macro-mechanical phenomena can be well explained by studying the micro-mechanical changes of construction waste.Construction waste mixture is similar to earth and stone mixture or coarse granular soil,which can be widely used as filler in a variety of engineering activities.It should be noted that the strength of construction waste material is a problem,and it is not suitable to be used as filler in high strength parts or key parts.