Numerical investigation on crack development and energy evolution of stressed coal-rock combination

2020 ◽  
Vol 133 ◽  
pp. 104417
Author(s):  
Heng Zhang ◽  
Cai-Ping Lu ◽  
Bin Liu ◽  
Yang Liu ◽  
Nong Zhang ◽  
...  
Keyword(s):  
Numerical Investigation ◽  
Crack Development ◽  
Energy Evolution ◽  
Coal Rock

scholarly journals Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2108
Author(s):  
Guanlin Liu ◽  
Youliang Chen ◽  
Xi Du ◽  
Peng Xiao ◽  
Shaoming Liao ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Damage Evolution ◽  
Rock Sample ◽  
Rock Fracture ◽  
Damage Threshold ◽  
Crack Development ◽  
Energy Evolution ◽  
Shear Cracks ◽  
Compression Tests ◽  
Microcrack Propagation

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

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

2019 ◽  
Vol 9 (20) ◽  
pp. 4427 ◽  
Author(s):  
Shang Yang ◽  
Jun Wang ◽  
Jianguo Ning ◽  
Pengqi Qiu
Keyword(s):  
Kinetic Energy ◽  
Failure Modes ◽  
Rock Strength ◽  
Compressive Loading ◽  
Dissipated Energy ◽  
Failure Behavior ◽  
Peak Strain ◽  
Energy Evolution ◽  
Coal Rock ◽  
Axial Splitting

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.

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

2020 ◽  
Vol 2020 ◽  
pp. 1-16 ◽  
Author(s):  
Shilin Song ◽  
Xuesheng Liu ◽  
Yunliang Tan ◽  
Deyuan Fan ◽  
Qing Ma ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Loading Condition ◽  
Failure Modes ◽  
Failure Process ◽  
Strong Support ◽  
Dissipated Energy ◽  
Energy Evolution ◽  
Cycle Index ◽  
Cyclic Loading Condition ◽  
Coal Rock

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.

scholarly journals Study on Rock Burst Event Disaster and Prevention Mechanisms of Hard Roof

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Nan Zhou ◽  
Hengfeng Liu ◽  
Jixiong Zhang ◽  
Hao Yan
Keyword(s):  
Rock Mass ◽  
Energy Release ◽  
Rock Burst ◽  
Strain Energy ◽  
Roof Rock ◽  
Coal Mass ◽  
Energy Evolution ◽  
Hard Roof ◽  
Working Face ◽  
Coal Rock

Coal mining under hard roofs is jeopardized by rock burst-induced hazards. In this paper, mechanisms of hard roof rock burst events and key techniques for their prevention are analyzed from the standpoint of energy evolution within geological conditions typical of the hard roofs found in Chinese coal mines. Equations used to calculate the total strain energy densities of the coal-rock mass and hard roof working face are derived. Moreover, several failure-causing energy evolution rules are analyzed under various conditions. Various rock roof and coal mass thicknesses and strengths are considered, and a method of preventing hard roof rock burst events is proposed. The results obtained show that rock burst events can be facilitated by high stress concentrations, significant accumulation of strain energy in the coal-rock mass, and rapid energy release during roof breakage. The above conditions are subdivided into two classes: energy accumulation and energy release. The total strain energies of the coal mass and working faces in the roof are positively correlated with the roof thickness, roof strength, and coal mass strength. The coal mass strength primarily influences the overall accumulation of energy in the working face, and it also has the largest effect on the total energy release (i.e., the earthquake magnitude).

scholarly journals Research on the Rockburst Tendency and AE Characteristics of Inhomogeneous Coal-Rock Combination Bodies

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Yun-liang Tan ◽  
Wei-yao Guo ◽  
Qing-heng Gu ◽  
Tong-bin Zhao ◽  
Feng-hai Yu ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Bonding Strength ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Energy Evolution ◽  
Evolution Law ◽  
Coal Rock ◽  
Exponential Relation ◽  
Compressive Tests

In order to research the influence of homogeneity on the rockburst tendency and on AE characteristics of coal-rock combination body, uniaxial compressive tests of inhomogeneous coal-rock combination bodies obeyed by the Weibull distribution were simulated using particle flow code (PFC2D). Macromechanical properties, energy evolution law, and AE characteristics were analyzed. The results show that (1) the elastic modulus homogeneitymEhas an exponential relation with macroscopic modulusE, and the bonding strength homogeneitymσhas an exponential relation with uniaxial compressive strengthσc; (2) the rockburst tendency of the coal-rock combination body will increase with the increase ofmEormσ, andmσis the leading factor influencing this tendency; and (3) both the change law of AE hits and lasting time in different periods of AE characteristics are influenced bymσ, butmEjust influences the lasting time. The more inhomogeneous the coal-rock combination body is, the shorter the lasting time in booming period of AE characteristics will be. This phenomenon can be used to predict the rockburst tendency of the coal-rock combination body.

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