Study on Mechanical Property of Coal-Rock Combination Under Different Unloading Confining Pressure Rate

• Published in: Geotechnical and geological engineering Vol. 41; no. 4; pp. 2629 - 2644
• Main Authors: Hu, Shanchao, Zhou, Xuedong, Ru, Wenkai, Han, Jinming, Guo, Shihao, Zhang, Chenxi, Yang, Lei
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.06.2023; Springer Nature B.V
• Subjects: Civil Engineering; Coal; Deformation; Deformation analysis; Earth and Environmental Science; Earth Sciences; Failure analysis; Geotechnical Engineering & Applied Earth Sciences; Hydrogeology; Original Paper; Rocks; Stress-strain curves; Terrestrial Pollution; Unloading; Waste Management/Waste Technology; Unloading confining pressure rate; Deformation characteristic; Failure characteristic; Coal-rock combination; Strength characteristic; Unloading test
• ISSN: 0960-3182; 1573-1529
• DOI: 10.1007/s10706-023-02417-5

In order to study the failure characteristics of coal-rock assemblage under the condition of unloading confining pressure. This study carries out the unloading confining pressure tests of coal-rock combination under three different pressure rates. The stress–strain curves of coal-rock combination in tests were observed, and the failure, deformation, and strength characteristics were analyzed. The result shows the combination has an obvious volume expansion phenomenon dominated by the simple shear failure of the coal part in the process of unloading the confining pressure. The rock part starts to damage with the increment of the confining pressure value and the unloading rate. The fracture angle of the sample is proportional to the initial confining pressure and inversely proportional to the unloading confining pressure rate; the fragmentation and intensity degree of coal-rock combination are significantly different under different test conditions. The fragmentation degree under the unloading confining pressure rate of 0.03 MPa/s, 0.06 MPa/s, 0.09 MPa/s is increased progressively, and the opposite trend appears on intensity degree. Axial deformation is dominant in the axial compression loading stage. The axial and circumferential deformations increase slowly at the stage of constant axial pressure, and the axial deformation is relatively larger. The circumferential deformation increases sharply at the stage of decreasing axial pressure. The internal friction angle is in direct proportion to the unloading rate, the cohesion and residual strength are in inverse proportion to the unloading rate, and the residual strength is in direct proportion to the initial confining pressure.