Experimental Study on Mechanical Properties, Failure Behavior and Energy Evolution of Different Coal-Rock Combined Specimens

Abstract

To investigate the effect of the pure coal/rock strength on the mechanical behavior, failure behavior, and energy evolution of coal-rock combined (CRC) specimens, an AG-X250 Shimadzu Precision Universal Test was used to conduct uniaxial compressive loading, uniaxial cyclic loading, and unloading compression experiments on pure coal, pure rock, and different CRC specimens. The results show that the uniaxial compressive strength, Young’s modulus, and peak strain of the CRC specimen mainly depend on the coal specimen instead of the rock strength. The major failure modes of CRC were the shearing fracture and axial splitting failure, and for the CRC specimen with the same hard rock, the CRC specimen severely failed due to axial splitting cracks. In addition, the released elastic energy Ue, dissipated energy Ud, and kinetic energy Ur increase with increasing rock mass/coal strength, and for CRC specimen with the same coal, the greater the difference in strength between the rock and coal is, the greater the kinetic energy is.

Water-bearing effect on mechanical properties and interface failure mode of coal–rock combination samples

“…When the axial load reached the peak strength of the coal body, it was not enough to cause the macroscopic failure of the rock mass, so the failure of C-RC only occurred in the coal body, indicating that the weakening degree of the coal-rock interface effect on the C-RC was less than the coal-rock strength ratio effect. At this time, the strength ratio of coal and rock mass was about 0.25 (critical value of rock mass failure), which was consistent with the research results of Yang et al (2019) on the failure law of C-RC under different strength ratios. At a water content of 4% (D-33-8), the C-RC was mainly damaged in the coal part; small fracture occurred when the crack extended to the rock part, and some rock fragments peeled off.…”

“…Yang et al (2020a) prepared "rock-coal-rock" composite samples with three height ratios in laboratory, carried out uniaxial compression test and PFC2D numerical simulation test of C-RC, and obtained the asymptotic instability characteristics and evolution law of AE energy under the influence of C-RC interface effect based on the analysis of "rock-coal-rock" combination AE signal and macro-failure characteristics. Yang et al (2019) conducted uniaxial compression and cyclic loading-unloading tests on coal, rock and three groups of C-RC, analyzed the mechanical parameters and energy evolution law of C-RC, obtained the energy storage characteristics of different samples, established and discussed the energy driving mechanism of C-RC failure based on the mechanical response, energy evolution, and deformation failure characteristics of C-RC.…”

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

“…Substitute Equation (4) into Equation ( 3) to obtain the expression of elastic energy, In the case of three-dimensional stress, according to the method suggested by Yang [35] and Cheng [36], the energy in the principal stress space can be expressed as follows:…”

Numerical Test Study on the Failure Mechanism of Coal-Rock Combined Body under the Coupling Action of Hydraulic and Mechanical

“…The coal body does not exist alone in the stratum but exists in the form of coal and rock coexistence. The disaster accident of roadway surrounding rock is the result of the interaction between the rock body and the coal body [1][2][3]. If only studying the physical and mechanical properties of coal body cannot effectively guarantee the safety of coal mine production, it is necessary to focus on the physical and mechanical properties of the "roof-coal" combination coal and rock mass [4][5][6][7][8][9][10].…”