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

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.