Mechanical Properties and Energy Evolution Law of Fractured Coal under Low Confining Pressure

Abstract

To study the mechanical properties and energy evolution characteristics of the shallow fractured coal in the Western China mining area, a series of triaxial compression tests was carried out on fractured coal specimens. The stress–strain curve, mechanical properties and failure characteristics were analyzed. Then, the fractal characteristics and energy evolution law were investigated. Results show that with the increase of prefabricated crack number, the post-peak stage of the stress–strain curve changed from a linear drop to a stepped drop, indicating that the damage degree tends to moderate. Both the elastic modulus and peak strength decreased as the prefabricated crack number increased, whereas the peak strain did not exhibit a clear trend. The failure mode changed from overall tensile failure to tensile-shear mixed failure as the prefabricated crack number increased. With the increase of prefabricated crack number, the failure shape dimension increased linearly. The total energy and elastic energy decreased gradually with the increase of prefabricated crack number, whereas the dissipation energy increased gradually. The results can provide a better understanding of the failure mechanism of fractured coal and its application for control design.

Study on the Co-Evolution Mechanism of Key Strata and Mining Fissure in Shallow Coal Seam Mining

“…From Formula ( 46), it can be seen that this formula is the relational formula between the stress intensity factor K II of the fissure tip of the unit body and the fracture angle β c of the rock formation. Similarly, the unit body stress and rock formation failure angle can be calculated using Formulas (19) and (22), respectively. Therefore, only the stress intensity at the tip of the fissure should be an unknown parameter.…”

“…For the distribution of fissures, after the mining of the working face, the overall fracture shape formed on the surface or its profile is defined, and related theories such as O rings, highlevel annular fissures, and elliptical belts are proposed [15][16][17]. On the basis of the above studies, many scholars have formed different research directions to study the evolution characteristics of fissures and formed the empirical formula prediction method and the key strata theoretical discrimination method mentioned in the three regulations to study the development height of fractures [18][19][20][21][22]. At the same time, in order to more comprehensively develop the influence of mining parameters on fissure evolution characteristics, the main influential factors of fissure evolution characteristics were obtained through corresponding research on mining height, mining depth, and working face length [23][24][25].…”

Burst Failure Characteristics and Energy Evolution Law of Coal with Prefabricated Cracks at Different Angles

“…Te fracture of coal can be regarded as a process of energy conversion and transmission, and its fnal failure is a state instability phenomenon driven by energy. Many scholars believe that the essential mechanism of coal dynamic failure and rock burst can be revealed from the perspective of energy [10][11][12][13][14]. Terefore, it is of great engineering signifcance to study the burst failure and energy evolution of cracked coal.…”

Different Stress Paths Lead to Different Failure Envelopes: Impact on Rock Characterisation and Design

“…This large variation often is linked to the heterogeneous nature of rock and the presence of micro-defects, pores, voids, flaws, layering, anisotropy, etc. (e.g., [1][2][3][4][5]). The strength of rock is a non-intrinsic property, which means that its value is influenced (1) by the geometric characteristics of the specimen (e.g., its volume, shape, and orientation), (2) by environmental aspects (e.g., humidity and temperature), (3) by the loading rate (e.g., conventional loading rates, dynamic loading, and creep), and (4) by the test set-up.…”