Study On Macro And Micro Mechanical Properties Of Soil-rock Mixture Based On Discrete Element Triaxial Test

Soil-rock mixture(SRM)is composed of relatively soft soil and relatively hard rock,which has obvious heterogeneity,non-uniformity and non-continuity,so its physical and mechanical properties are very complicated.Soil-rock mixture is widely distributed in nature,especially in the southwest region,where many excavation and filling projects involve it.Therefore,it is of great significance to study the macro and micro mechanical properties of soil-rock mixture and its failure mechanism in different engineering environments,so as to prevent the safety accidents of soil-rock mixture engineering and reduce the loss of people’s lives and property.Supported General funding from the Chinese Postdoctoral Science Foundation for "Fine Modeling of Macrogranular Soil Microstructures and Evaluation of High Fill Slope Stability(No.2020M673110)",this paper establishes a discrete element model based on the real block shape and flexible boundary conditions,and carries out discrete element triaxial numerical tests under flexible boundary conditions,and systematically explores the macro and micro mechanical properties and deformation failure mechanism of soil-rock mixture.The main research contents and conclusions are as follows:(1)The flexible boundary is realized by using a coupled wall method.Based on reverse reconstruction engineering,a discrete element triaxial test model of soil-rock mixture with a real block shape and flexible boundary is established,and the indoor triaxial test is successfully restored.(2)The effects of size effect,loading speed and length-diameter ratio of sample length to diameter ratio on the macro and micro mechanical properties of soil-rock mixture were analyzed.The results show that: the influence of size effect has an upper limit.When the sample exceeds a certain size,the influence on cohesion and internal friction Angle of soil-rock mixture gradually becomes stable.The limit value of the impact of loading speed on the strength index is 0.1m/s.When the loading speed is less than 0.1m/s,the impact on cohesion and internal friction angle is relatively small.When the loading speed is greater than 0.1m/s,the impact on the strength index is relatively large When the length-diameter ratio is less than 2.0,the peak value of deviator stress is larger and the shear shrinkage is more obvious.When the length-diameter ratio is more than 2.0,the curve has obvious plastic deformation and the plastic characteristics of the sample are more obvious.(3)The effects of rock content,block shape and maximum particle size of the block on the macro and micro mechanical properties of soil-rock mixture were analyzed.The results show that: with the increase of the stone content,the skeleton effect of the block stone becomes more obvious,and the shear strength of the sample gradually increases.When the rock content exceeds 60%,the indirect contact force distribution of the particles is extremely uneven,and the curve exhibits significant fluctuations.The more prominent the angularity of the block stone,the greater the mutual contact force between particles,and the greater the occlusive effect it exerts.Under different maximum particle sizes,the particle movement appears inclined and asymmetric phenomena.The maximum particle size of a block has a more significant impact on the cohesion,but has a smaller impact on the internal friction angle.(4)Through secondary development,axial and circumferential servo mechanisms are used to realize axial and circumferential loading and unloading control under different stress paths,and discrete element triaxial tests under different stress paths are carried out.The results show that under the equal k stress path,the sample mainly undergoes volumetric compression deformation,and the larger the q/p ratio,the greater the degree of compression.The sample exhibits obvious shear shrinkage characteristics,and there is no obvious shear band inside the sample.The mechanical properties of the soil-rock mixture under the equal p stress path are similar to those under the conventional stress path,but the shear dilatancy will be more obvious.The final failure surface of the sample is mainly a conjugate shear surface formed after the microcracks are interconnected and connected.Under the unloading path,the strength of the soil-rock mixture decreases significantly,indicating that the soil-rock mixture is more likely to be destroyed under unloading,and its physical and mechanical properties are obviously different under different unloading stress paths.