Experimental study on mechanical damage properties and energy evolution characteristics of coal-rock combination under different interface conditions

This is the authors' abstract. We don't add key points for this paper.

Indirect fracturing technology is a crucial method for enhancing gas extraction efficiency in broken soft coal seams. The cracks initiate from the roof strata, traverse the coal-rock interface, and ultimately penetrate the coal seam. In this process, the propagation path is influenced by the interface cementation strength and structure characteristics. Then, investigating the mechanical properties and damage evolution of the coal-rock combination under varying interface conditions holds significant engineering importance. In this paper, industrial CT, three-dimensional reconstruction, and 3D printing technologies are employed to prepare combination samples that retain primary interface structure. Uniaxial compression experiments are conducted sequentially under various interface conditions, with real-time monitoring of the samples using an acoustic emission (AE). The results indicate that the peak strength ranking, from highest to lowest, is as follows: smooth-pouring (S-P) > primary-vaseline (P-V) > smooth-vaseline (S-V). The compressive strength of sample S-V is only 2.22 MPa, which is 1.47 MPa and 0.59 MPa lower than that of samples S-P and P-V, respectively, indicating a significant decrease. Conversely, the strain arrangement follows an opposite order. The strains for samples S-P and P-V are 0.11 and 0.19, respectively, while sample S-V exhibits the largest strain, reaching 0.21, which is twice that of sample S-P. There are no signs of relative sliding in sample S-P, which mainly exhibits shear cracks. In contrast, both samples S-V and P-V display evidence of relative sliding, with exhibiting tension and composite cracks, respectively. Moreover, the evolutionary characteristics of the AE signals exhibit a strong correlation with the failure types of the samples.