Abstract
To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.
Highlights
The deep underground engineering rock mass is in a three-way stress state [1,2,3,4]
Excavation of slopes, tunnels, or mines causes strong expansion of rock mass in the area adjacent to excavation surface, accompanied by complex mechanical failures such as tension and shear. erefore, to study the mechanical properties of deep underground engineering rock mass, it is not enough to rely on uniaxial compression, tensile tests, or conventional triaxial compression tests only
There are relatively few true triaxial test studies on the influence of intermediate principal stress on coal mechanical properties. erefore, in this study, coal was taken as the research object; through true triaxial loading and unloading tests, the transient unloading failure of coal under the original rock stress state is simulated [26, 27], and acoustic emission detection technology was used to evaluate the effect of intermediate principal stress on coal strength and failure. e true triaxial test is used to study the influence of the intermediate principal stress on the mechanical properties of coal, which is of great significance to the safe mining of coal mines
Summary
The deep underground engineering rock mass is in a three-way stress state [1,2,3,4]. Wang et al [16] used a true triaxial testing machine to perform a series of loading and unloading tests on rock samples under compression and shear and obtained the variation trends of elastic shear modulus at different unloading stages. Xue and Liu [21] used a true triaxial testing machine to simulate the underground stress conditions of a mine and combined with acoustic emission equipment made an early warning of coal mass destruction. Erefore, in this study, coal was taken as the research object; through true triaxial loading and unloading tests, the transient unloading failure of coal under the original rock stress state is simulated [26, 27], and acoustic emission detection technology was used to evaluate the effect of intermediate principal stress on coal strength and failure. There are relatively few true triaxial test studies on the influence of intermediate principal stress on coal mechanical properties. erefore, in this study, coal was taken as the research object; through true triaxial loading and unloading tests, the transient unloading failure of coal under the original rock stress state is simulated [26, 27], and acoustic emission detection technology was used to evaluate the effect of intermediate principal stress on coal strength and failure. e true triaxial test is used to study the influence of the intermediate principal stress on the mechanical properties of coal, which is of great significance to the safe mining of coal mines
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