Experimental Study On Deformation Characteristics Failure Of Rock Under The Complicated Loading

As a non-homogeneous brittle material, rock in many engineering fields is related to the cyclic loading and shear loading conditions about deformation and failure problems. In this paper, based on experimental and theoretical analysis, it is studied on the effects of different levels of maximum stress, the length of the different samples on rock deformation and failure characteristics and acoustic emission characteristics under different experimental conditions such as cyclic loading conditions, uniaxial compression by Shimadzu Precision AG-I 250kN Universal Testing Machine, American Physical Acoustics PCI-2 type of acoustic emission testing system, and Self-developed rock shear test system. It is also researched on the damage evolution law under cyclic loading conditions by using of acoustic emission as the macro performance of rock failure. Also it is studied on the development of micro-cracks in the temporal and spatial evolution law of the micro-observation in the shear loading conditions. The main results obtained are as follows:(1) The material testing machine itself will be deformed while used to do uniaxial compression tests. Material testing machine and the rock specimen can be seen as series system. As material testing machine stiffness is not big enough relatively to rock samples, so when analysis of deformation of rock samples the displacement of testing machine can not be ignored. The load - displacement relationship of material testing machine in load during was determined by this experiment, and it is also given the empirical formula which is prepared for deeper analysis of the experimental data.(2) In cyclic loading conditions, the maximum stress plays a dominant role on the rock specimen deformation and determines the development trend of rock failure, which can be seen in acoustic emission characteristics of the rock failure. When maximum stress is large, it is acoustic emission signals in the cycle of each process; the ceiling low, especially near the threshold value, it is less acoustic emission signal, excepted when the only apparent close to destruction.(3) Different sizes of rock specimen have a significant effect on emission characteristics during its deformation. The failure modes of rock and acoustic emission model will also different because of the length of rock specimen.(4) In the shear process, the normal stress greater, the higher the shear strength of rock. Lateral friction experiment will make the measure of the shear strength of rock larger than the actual values, which can be added friction to low friction of agents. In the shear process, the generation and development of rock crack in the shear process is instantaneous, because the rock is brittle material. Crack is extended upward from the bottom of the specimen until throughout the rock specimen.