Failure characteristics of three-body model composed of rock and coal with different strength and stiffness

Wan

Advances in Materials Science and Engineering

et al. 2018

In underground coal mining systems, the occurrences of coal burst hazards and pillar failures relate not only to the condition of stress distribution but also the geometry of roof-coal-floor structures. To study the failure response of these structures, the rock-coal-rock (RCR) sample, in which a coal component is sandwiched between rocks, is always employed as the experimental subject. In this study, the effect of height ratio (a ratio represents the height percentage of coal component in an RCR sample) on the mechanical properties and deformation behavior of RCR samples was numerically investigated by using the distinct element model (DEM). The results reveal the following. (1) The uniaxial compression strength (UCS) of the RCR sample decreases with increasing height ratio as an inverse proportional function. (2) With increasing height ratio, the elastic modulus of the RCR sample decreases exponentially, while the postpeak modulus is strengthened in an inverse proportional manner. (3) Microcracking activity of the RCR sample is different from that of the pure sample during loading. Specifically, a reactive period always occurs after the quiet and active periods in the RCR sample. (4) The RCR sample fails in a progressive manner, in which cracking bands develop preferentially in coal and then extend to rocks. Expectably, the mechanical properties and failure behavior of RCR samples are height ratio dependent, which may contribute to predicting the hazard of coal bursts and estimating the failure of rock-coal-floor structures.

Section: Resultsmentioning

confidence: 99%

“…Briefly, these foregoing investigations demonstrated that the UCS and failure behavior of composite samples are material properties dependent. However, these studies have been mainly concentrated on either the effect of material property or the damage of coal [19,20].…”

Section: Introductionmentioning

confidence: 99%

Mechanical Properties and Failure Behavior of Composite Samples

Wan

Advances in Materials Science and Engineering

et al. 2018

“…erefore, the loading test of coal-rock combinations is presented, which is more consistent with the deformation and failure of an in situ coal seam and its surrounding rocks [22][23][24]. Chen et al [25] studied the mechanical properties of coal-rock combinations with different height ratios and found that the uniaxial compressive strength and Young's modulus of the samples increased with increasing rock-coal height ratio.…”

Section: Introductionmentioning

confidence: 83%

Study on Failure Modes and Energy Evolution of Coal-Rock Combination under Cyclic Loading

Song

Liu

Tan

et al. 2020

Shock and Vibration

The loading modes and roof lithology have a significant influence on the mechanical properties of coal seams. To reveal the failure modes and energy evolution law of underground coal during the mining process, conventional uniaxial and uniaxial cyclic loading tests were carried out on three types of samples: coal, rock, and coal-rock combinations. The results show that the samples mainly behave with three failure modes (shear slip, tensile splitting, and fracture), and all the coal sections in the coal-rock combinations fail, whereas most rock sections remain intact. The compressive strength of the coal-rock combination is higher than coal and much smaller than rock. Compared with the conventional uniaxial loading condition, both the maximum deformation before failure and Young’s modulus under the cyclic loading condition are greater, and the latter increases quadratically with the cycle index. The energy densities are also calculated, and their variations are analysed in detail. The results show that with increasing cycle index, both the elastic energy stored in the sample and the dissipated energy increase in a quadratic function, and the failure process becomes more intense. This research reveals the failure modes, deformation characteristics, and energy evolution of the coal-rock combination under different loading conditions, which can provide strong support for controlling underground surrounding rocks of the coal face and roadway in coalmines.

Advances in Civil Engineering

“…A lot of investigations have been performed in the past on the mechanical behaviour of composite structures composed of coal seam and surrounding rock strata [1][2][3][4][5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21]. In previous laboratory tests and numerical simulations, the composite structure was generally simplified as a composite sample of rock and coal with a bonded or frictional interface in order to study its mechanical behaviour [1][2][3][4][5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21]. e effects of rock strength and rock to coal height ratio on the strength and failure characteristics of rock-coal composite samples were studied by Liu et al [2] and Chen et al [11], respectively.…”

Section: Introductionmentioning

confidence: 99%

An Experimental Study of the Uniaxial Failure Behaviour of Rock‐Coal Composite Samples with Pre‐existing Cracks in the Coal

Chen

Yao

Yin

et al. 2019

Many hazards encountered during coal mining can be caused by the instability and failure of the composite structure of the coal seam and the surrounding rock strata. The defects present in the coal affect the structural stability of the composite structure. In this study, uniaxial compression tests were conducted on sandstone-coal composite samples with pre-existing cracks in the coal, combined with tests performed with an acoustic emission (AE) device and a digital video camera. The strength, macrofailure initiation (MFI), and failure characteristics of composite samples, as influenced by the coal’s pre-existing cracks, were analysed. The coal’s pre-existing cracks were shown to reduce the strength, promote the occurrence of MFI, and affect the failure characteristics of the samples. Vertical penetration cracks had much more pronounced effects on strength and MFI occurrence, especially vertical penetration cracks that penetrated through the centre of the coal. Horizontal penetration cracks had a much reduced effect on strength and MFI occurrence. The MFI caused a step shape in the stress-strain curve accompanied with a peak energy index signal and occurred around the original coal cracks. The MFI models predominantly exhibited crack initiation from the pre-existing coal cracks and surface spalling caused by crack propagation. The intact composite sample failure presented as an instantaneous failure, whereas the composite samples containing the pre-existing cracks showed a progressive failure. The failures of composite samples occurred predominantly within the coal and displayed an X-typed shear failure accompanied by a small splitting failure. Both the coal and sandstone were destroyed in the composite sample with vertical penetration cracks through the centre of the coal. Failure of the coal occurred through a splitting failure accompanied by a small X-typed shear failure, while the sandstone showed a splitting failure induced by crack propagation in the coal.