Experimental Study of the Dynamic Tensile Mechanical Properties of a Coal Sandstone Disc with a Central Hole

Jiehao Wu,Qi Zong,Ying Xu,Zhijie Wen

doi:10.1155/2020/8851575

Jiehao Wu, Qi Zong + Show 2 more

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https://doi.org/10.1155/2020/8851575

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Abstract

Deep mine rocks are often subjected to rock burst induced by dynamic load. The existence of initial holes will reduce the mechanical properties of rocks and affect the stability and safety of the tunnel excavating. In order to study the effect of the ratios of inner and outer diameter on disc specimen dynamic mechanical properties and failure modes, we use cylindrical sandstone specimens of Φ50 × 25 mm to process center holes of different diameters, and a series of dynamic splitting test were carried out with a system of split Hopkinson pressure bar (SHPB) with the diameter of Φ50 mm when the pressure is 0.15 MPa, 0.3 MPa, and 0.5 MPa. The results show that (1) the dynamic tensile stress-time-history curve exhibited double peak phenomena, and the second peak value is less than the first peak value, (2) the dynamic tensile stress peaks decrease nonlinearly with the increasing of the ratios of inner and outer diameter, and the dependence is more obvious when the pressure is higher, and (3) there is a tensile crack running along the loading direction in the failure modes of the five samples with the ratio of inner to outer diameter under three kinds of impact pressure. Under the same impact pressure, when the ratio of inner diameter to outer diameter is greater than the critical ratio of inner diameter to outer diameter, there is an obvious empty hole effect; that is, the sample develops secondary tensile cracks that develop from the upper and lower ends of the pore disc to the center of the inner hole. With the increase of the ratio of inner diameter to outer diameter, the width of the penetration crack increases. With the increase of impact pressure, the critical ratio of inner diameter to outer diameter decreases gradually. The research results have certain significance for understanding the mechanical properties of porous rocks.

Highlights

With increasingly deep coal mining, accidents due to typical dynamic hazards such as rock burst are prone to occur under dynamic loads such as engineering blasting. ese hazards have the characteristics of being sudden, rapid, and violent and have a serious impact on coal mine production safety [1]
Within the scope of this test, the test data for the specimens with different d/D values under the same gas gun pressure basically exhibited the same behavior, and the test data for the ring specimens with the same inner hole diameter under different gas gun pressures basically exhibited the same behavior. us, the test data for the specimens with five different d/D values, the solid disc specimens with a gas gun pressure of 0.3 MPa, and the test data for the ring specimens with d/D 0.16 at the three pressures were used for the analysis
As the gas gun pressure increased, the failure modes of the specimens were still type A or type B, and the critical d/D value decreased . at is, the circular central hole increasingly affected the free

Summary

Introduction

With increasingly deep coal mining, accidents due to typical dynamic hazards such as rock burst are prone to occur under dynamic loads such as engineering blasting. ese hazards have the characteristics of being sudden, rapid, and violent and have a serious impact on coal mine production safety [1]. Ese initial defects constitute weak points in the rocks and significantly reduce the strength and increase the ductility of the rocks These rocks are discontinuous, heterogeneous, anisotropic, and highly nonlinear. E evolution process is the precursor and prerequisite for the localization and instability of the rock mass, and it plays a decisive role in the ultimate failure mode of the rock mass [2,3,4]. These initial defects are considered to be especially important structures that control the strength of a rock. The small defects in the rock mass will be activated and will connect to form a large connected discontinuous surface [6]

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Results

Conclusion