Abstract
In this research, a uniaxial acoustic emission experiment was conducted on rock samples with different positions and diameters of the hole, and an analysis was made on the impact of different hole positions and diameters on the mechanical properties, failure, energy conversion, and acoustic emission-caused damage characteristics and laws of the rock samples. The results reveal as follows: first, due to the existence of holes in rocks, the stress-strain curve changes at each stage, accompanied by multiple stress drops. And the peak strength gradually reduces with the increase in hole diameter. At different hole positions, the duration that the rock sample passes through at each stage of the stress-strain curve varies, and the peak strength of the rock with the vertical hole is greater than that of the rock with the horizontal hole. This indicates that the bearing capacity and stability of the rock sample with the vertical hole are greater than those of the rock sample with the horizontal hole of the same diameter. Second, by making a comparison on the failure characteristics of rock samples, it is found that the intact rock shows brittle failure. For the rock sample with the horizontal hole, symmetrical tensile cracks initially appear in the upper and lower parts of the hole and finally form shear failure. As for the rock sample with the vertical hole, Y-shape failure originally presents and eventually forms N-shape failure with the increase in hole diameter. Over a comparison with the failure pattern of an intact rock sample, it is demonstrated that the final failure pattern and crack expansion trend on the rock sample vary with the change in the hole position and diameter. Third, as obtained by comparing and analyzing the energy conversion of the rock with different diameters of the hole, the energy conversion in the rock is changed due to the existence of holes, and the increase in hole diameter causes a gradual decrease in the elastic energy stored in the rock and gradual increase in the dissipated energy. And by comparing the energy conversion of the rock with different positions of the hole, it is acquired that the elastic energy conversion ratio of the rock with the vertical hole is higher than that of the rock with the horizontal hole. Furthermore, an explanation was made on the difference in the failure processes of the two types of rocks from the perspective of energy conversion.
Highlights
Heilongjiang Ground Pressure & Gas Control in Deep Mining Key Lab, Heilongjiang University of Science & Technology, Harbin 150022, China
A uniaxial acoustic emission experiment was conducted on rock samples with different positions and diameters of the hole, and an analysis was made on the impact of different hole positions and diameters on the mechanical properties, failure, energy conversion, and acoustic emission-caused damage characteristics and laws of the rock samples. e results reveal as follows: first, due to the existence of holes in rocks, the stress-strain curve changes at each stage, accompanied by multiple stress drops
Over a comparison with the failure pattern of an intact rock sample, it is demonstrated that the final failure pattern and crack expansion trend on the rock sample vary with the change in the hole position and diameter
Summary
Considering the influence on mechanical properties of the rock sample with the hole, the processed rocks were bored in two steps. According to regulations relevant to the mechanical test on rocks and considering the test error caused by experimental loading equipment, data acquisition, and a series of manual misoperations, the quantity of rock samples prepared for the experiment was not less than 4 and that used in the experiment was not less than 3. En, the evolution rule of the entire rock failure was observed via the camera in combination with the acoustic emission system and electrohydraulic servo press (see Figure 2). In the experiment, the uniaxial compression device and acoustic emission device were started at the same time in order to ensure the preciseness of the experiment and the consistency in the experimental data. In the experiment, the uniaxial compression device and acoustic emission device were started at the same time in order to ensure the preciseness of the experiment and the consistency in the experimental data. e impact of the external environment on the correctness of the experimental result and personnel walking around were reduced as much as possible, and the door and windows were closed during the experiment
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