Particle Breakage Characteristics Of Soil-rock Mixture In Waste Slag Dam Under Triaxial Test

In the construction of pumped storage power station,the slag generated by excavation accumulates to form a waste slag dam,which is easy to break particles under load and change its gradation structure.In case of rainstorm and flood,it is easy to induce dam instability and cause dam failure.To improve the understanding of the effects of particle breakage and dilatancy characteristics on the mechanical behavior of soil-rock mixture,a series of triaxial tests with different confining pressure,dry density and moisture content were carried out by using large triaxial test equipment.By analyzing the shear strength parameters obtained from the test and the gradation changes before and after shearing,the mechanism of soil-rock mixture in waste slag dam is studied.There is obvious particle breakage in triaxial test.The effects of dry density and water content on particle breakage are studied.The existing particle breakage indexes are compared and analyzed,and based on the change of particle size distribution before and after shearing,the gradation change and particle breakage are quantitatively described.Analyze that mechanical characteristics of particle breakage,the research shows that-particle breakage is one of the reasons that affect the strength non-linearity;and the friction angle decreases with the increase of particle breakage.The relationship between input plastic work and particle breakage was explore.The relationship among initial void ratio,particle breakage index and failure dilatancy rate was studied.A triaxial numerical model of soil-rock mixture is established by discrete element method,and the micro-failure characteristics of soil-rock mixture under different confining pressures and porosity are studied to reveal its internal deformation mechanism.The main research contents of this paper are as follows:(1)Through large-scale triaxial tests,the soil-rock mixture of waste slag dam with differentdry density and water content is studied.The stress-axial strain curve of the sample shows strain hardening.Different confining pressures,dry densities and water contents have different mechanical responses to soil-rock mixture,and have significant effects on peak principal stress difference and strength parameters.and different confining pressure,dry density and water content have different mechanical responses to the soil-rock mixture,which has significant effects on the peak principal stress difference and strength parameters.(2)Based on the grading curve before and after shearing,the analysis shows that the particle breakage of soil-rock mixture is greatly influenced by dry density and confining pressure.Summarize and compare the existing particle breakage indexes,derive the expression of gradation equation,and establish the conversion relationship between breakage index Bc and fractal dimension D.The crushing index Bc and fractal dimension D are used to quantitatively analyze the crushing situation of the soil-rock mixture of the waste slag dam after shearing.The results show that the particle breakage index Bc and fractal dimension D increase with the increase of confining pressure,and the particle breakage index Bc and fractal dimension D have a hyperbolic relationship with the confining pressure σ3/Pa.There is a sequence of effects of initial void ratio and particle breakage on the shear behavior of samples.(3)The influence of particle breakage on the mechanical properties of soil-rock mixture of waste slag dam is studied.The internal friction angle decreases with the increase of particle breakage index.There is a hyperbolic relationship between breakage index Bc and plastic work Wp,and particle breakage increases with the increase of plastic work.The dilatancy deformation of the sample is described by the failure dilatancy ratio,and there is a good linear relationship between the failure dilatancy ratio and the initial void ratio of the sample,and a good power function relationship between the failure dilatancy ratio and the breakage index Bc.The failure dilatancy rate increases with the increase of initial void ratio and breakage index.(4)Based on the clump templates and flexible membrane model servo method,the triaxial discrete element numerical simulation of soil-rock mixture is carried out.The micro-deformation and failure characteristics of soil-rock mixture under triaxial stress state are studied.The final shape of the sample bulges laterally,forming an "X"-shaped shear band,and the development of the shear band decreases with the increase of porosity.Through the particle movement and the change of spatial particle displacement vector and particle velocity vector,the development and change law of the internal structure of soil-rock mixture is expounded from the micro level.Through the evolution and development of force chain,the micro mechanism is revealed.With the increase of axial strain,the bond chain at the upper and lower ends of the specimen is relatively complete,and the bond chain at the middle part is broken,resulting in shear failure.