Size Effect And Acoustic Emission Characteristics Of Rock Under Uniaxial Compression

Rock is a complex geological body,which is a typical macroscopic continuous microscopic discontinuous non-uniform medium.The size effect of rock means that the mechanical properties of rock specimens will show obvious differences according to the size and shape of the specimens.This difference leads to the inability to directly apply the research results of rock mechanics in the laboratory to engineering practice.Moreover,there are many kinds of rocks and complicated environments.It is difficult to study the damage of rocks of various scales under experimental conditions.The rock size effect is still a problem that needs to be further studied.Therefore,it is necessary to carry out further systematic research on the size effect.Based on the question above,this paper uses the combination of physical experiments and numerical experiments to study the size effect.The main research contents and conclusions are as follows:（1）The effects of loading rate,homogeneity and gasket material on the mechanical properties（peak load,peak strain,failure mode）and acoustic emission parameters of rock uniaxial compression combined with acoustic emission experiments were studied by orthogonal experiment.The results show that the factors affecting the peak load strength of the rock are the homogeneity>loading rate>soft and hard material of the gasket.At the same time,it also shows that the cumulative coefficient of acoustic emission and the discrete energy of acoustic emission are used to evaluate the acoustic emission simulation results.The dispersion is better,and the homogeneity is 3,the loading rate is 0.002mm/step,and the gasket is selected as the hard gasket.The experimental result data is less discrete.（2）RFPA2D and RFPA3D were used to study the variation of mechanical parameters such as failure mode,acoustic emission parameters,peak intensity and peak strain with the aspect ratio of rock specimens with different widths at the same bottom.The results show that the mechanical parameters y of the rock with the aspect ratio x can be expressed by the mechanical parameters such as peak load and peak strain with an aspect ratio of 2,likey（28）ay₀exp（b*（2-x））（10）c.At the same time,it is also shown that with the increase of the aspect ratio,the failure mode of the specimen gradually changes from the X-conjugate shear failure to the single shear plane,and the peak strength and peak strain decrease with the increase of the aspect ratio.（3）RFPA2D is used to study the variation of mechanical parameters such as failure mode,acoustic emission parameters,peak intensity and peak strain of rock specimens with different aspect ratios with height-to-width ratio.The results show that the peak load and peak strain of rock increase with the increase of rock size are firstly reduced and gradually stabilized.There is a threshold between the width.Below this width,the peak load of rock increases with size.There is a negative correlation,and the peak load of the rock larger than this threshold tends to a certain stable value.（4）The deformation and failure process of rock is analyzed from the energy point of view.The results show that the elastic strain energy,the dissipative energy and the total energy of the system decrease with the increase of the aspect ratio,but the proportion of dissipated energy increases with the increase of the aspect ratio and stabilizes to a fixed value.The greater the proportion of dissipated energy,the more inclined the rock is to single shear plane damage.When the ratio of width to height of the specimen is kept constant,the mechanical properties of the rock will be slightly different due to the increase of the dissipative energy ratio.However,when the rock specification reaches a certain level,the dissipative energy ratio of the rock is higher.Will be fixed,resulting in the mechanical properties of the rock,the way of destruction is more consistent.