Experimental study on deformation and failure characteristics of heterostructure in borehole sealing section

Gas drainage borehole sealing section is a heterostructure composed of coal-cement-extraction pipes. In order to study the deformation and failure characteristics of the coal-cement heterostructure in borehole sealing section, the combination of Vallen AMSY-6 acoustic emission signal acquisition system and TAW-2000 high temperature rock triaxial servo testing machine were used to conduct acoustic emission tests of deformation and failure of coal monomer, cement monomer and coal-cement composite specimen under uniaxial load. The test results show that the peak stress of the coal-cement composite specimen is between the coal monomer specimen and the cement monomer specimen, and the strength of the coal monomer specimen is 2.1 times that of the cement monomer specimens. The coal-cement strain composite specimen and the body strain drop point of the coal monomer specimens are accompanied by a sharp increase in the ringing count of acoustic emission, while the acoustic emission index of the cement monomer specimen increases more gently, and the different specimens are at the peak stress. The acoustic emission index reaches the maximum value, and the peak ringing count of the coal-cement composite specimen is about 112 times of the cement monomer test piece; the stress-strain curves of the coal-cement combination test piece and the coal monomer test piece show brittle deformation characteristics after the peak, while the stress-strain curve of the cement monomer specimens show plastic deformation characteristics after the peak. The failure mode of the coal-cement heterostructure specimen is shear failure, and the failure mode of the coal monomer specimen is "X"-shaped conjugate shear failure and tensile failure. The failure mode of the cement monomer specimen is tensile failure. At present, most of the hole sealing materials for coal mine gas drainage in China are cement-based sealing materials. The strength of the coal-cement heterogeneous structure in the borehole sealing section is affected by both the properties of coal body and cement materials. In the selection of underground cement-based sealing materials, the cement-based sealing materials with a small difference in strength from coal and rock after solidification can be selected preferentially.