Research On Mechanical Properties And Collapse Mechanism Of Sand-gravel Mixture Based On Discrete Element Method

In recent years,stratum instability has often occurred on roads and nearby buildings and structures,ranging from uneven settlement to severe,sudden collapse,causing casualties.The suddenness and randomness of the collapse further exacerbated the hazard of the collapse.Frequent collapse accidents threaten the safety of the people's property and lives at all times.Improving the resilience of urban roads to disasters,analyzing the law of collapse,and ensuring normal production and living conditions is a top priority.Stratums can be divided into lightly disturbed strata,modified strata,and remodeled strata.The particle size,composition,and mechanical properties of the remodeled strata are very different.Therefore,the remodeled strata have more conditions for collapse.Sand-gravel mixture stratum is a typical remolded stratum,but there are few studies on the collapse of sand-gravel mixture stratum.At the same time,the mechanism of the disaster-pregnancy chain of ground collapse is very complicated,and the existing research cannot satisfy the prediction and prevention of the collapse.Therefore,the physical properties of sand-gravel mixtures and mechanism of ground collapse,with great scientific and practical significance.This paper mainly uses DEM simulation and model tests to conduct in-depth research on the mechanical properties and collapse mechanism of sand-gravel mixtures:(1)Consider the influence of gravel shape and particle size on the mechanical properties and deformation laws of sand-gravel mixtures.Use digital image processing technology to store the true shape of the gravel in the gravel shape database and reconstruct it in the discrete element software to complete the construction of the sand-gravel stochastic model;combine the fractal theory to construct the dual fractal structure model of the sand-gravel mixture,and use the sand particle size analysis The dimension value and the fractal dimension value of the gravel particle size determine the particle size distribution of the sand-gravel mixture,and the particle gradation can be quantitatively analyzed in the subsequent simulation.(2)Based on the PFC direct shear test,the change law of the shear strength parameters with the particle size fractal dimension and the axial coefficient is obtained,and the internal mechanism of this change is analyzed in terms of particle displacement,contact number and particle rotation.(3)The model test is used to analyze the collapse mechanism of the sand-gravel mixture,and the test variable is the depth of the buried depth.In view of the change law of the collapse shape,displacement,earth pressure,and loss amount during the collapse process,the influence of the depth of burial height is discussed.(4)The discrete element simulation method is used to construct a sand-gravel mixture collapse model to further summarize the change characteristics of the shape,loss,soil stress and displacement during the collapse.The effect of buried depth,opening size,and particle gradation on surface subsidence is described.