Fractal Characteristics And Shear Characteristics Of Soil-rock Mixture

With the construction of various large-scale domestic projects in recent years,more and more geotechnical projects are inevitably involved in soil-rock mixtures.Due to its unique structural characteristics,the soil-rock mixture can easily cause geological disasters such as collapse,landslide,and debris flow under the disturbance of earthquake,rainfall,reservoir water level fluctuation and engineering excavation.Therefore,studying the strength characteristics and shear characteristics of soil-rock mixture is of great significance to avoiding and preventing disasters of soil-rock mixture.This paper relies on the outstanding young talent fund project of the Science and Technology Department of Jilin Province "Study on the Influence of the Meso-structure of Soil-Rock Mixture on Macro-mechanical Properties"(20180520073JH),taking the soil-rock mixture in Jingyuetan area of Changchun City as the research object,and analyzing based on fractal theory The fractal characteristics of the soil-rock mixture and the soil-rock mixture with different rock content and the relationship between the particle size fractal dimension and the rock content in the Jingyuetan area.Through the large-scale direct shear test of coarse-grained soil,the shear strength characteristics of soil-rock mixture under different normal pressure and rock content are studied,and the influence of fractal dimension on the shear strength parameters of soil-rock mixture is analyzed.The PFC2 D numerical simulation software is used to carry out large-scale direct shear numerical experiments,and the numerical simulation results are compared with the indoor test results to verify the reliability of the numerical model.Based on this numerical model,the particle movement,fragmentation law and crack evolution law during the shearing process are studied,and the shearing mechanism of the soil-rock mixture is revealed.Through the research in this article,the aim is to provide a reference for the analysis of the slope stability of the soil-rock mixture,and the following conclusions are mainly obtained:(1)The particle size distribution of the soil-rock mixture in Jingyuetan area of Changchun City has fractal characteristics,and the particle size fractal dimension is between 2.0 and 2.6.The soil-rock mixture generally has two-dimensional fractal characteristics.When the content of block stone reaches 50% to 60%,the particle size distribution curve is approximately a straight line.At this time,the soil-rock mixture has one-dimensional fractal characteristics,and its uniformity is the best.(2)Through the large-scale direct shear test of coarse-grained soil,it can be seen that with the increase of block stone content,the shear strength,cohesion and internal friction angle all increase first and then decrease.The soil-rock mixture has an optimal soil-rock ratio,that is,when the rock content is about 50%,the shear strength parameters all achieve the maximum value.With the increase of the fractal dimension of the coarse-grained rock,the shear strength parameters of the soil-rock mixture show a parabolic relationship as a whole,which all increase first and then decrease.The particle size and particle size distribution of the block stone also have an impact on the shear strength of the soil-rock mixture.(3)The soil-rock mixture has obvious dilatancy characteristics.When the rock content is the same,with the increase of the normal pressure,the dilatancy characteristics of the sample weaken,and the greater the normal pressure,the more obvious the shear shrinkage characteristics.Under the same normal pressure,with the increase of block stone content,the dilatancy characteristics of the soil-rock mixture gradually increase,and the increase of block stone content strengthens the dilatancy characteristics of the soil-rock mixture.During the shearing process,the block stone particles will be broken.According to the crushing characteristics of particles,it can be divided into four types: disintegration crushing,fracturing crushing,local fracture and surface friction.(4)During the shearing process,the block stone particles inside the soil-rock mixture sample squeeze,roll,overrun and rotate with each other,and the block stone particles have different degrees of fragmentation under the occlusal effect.According to the crushing characteristics of particles,they can be divided into three types: slight crushing,partial crushing and complete crushing.During the shearing process of the soil-rock mixture sample,as the shear displacement increases,the crack propagation depth increases;as the normal pressure increases,the crack propagation depth increases;with the increase of the rock content,The propagation depth of the crack is reduced.And in the shearing process,the interaction between the particles is accompanied by a variety of energy changes.