Experimental investigation on the fracture propagation characteristics of sealed sections in gas drainage boreholes

The stability of sealed sections in gas drainage boreholes is one of the key factors affecting the efficiency of gas drainage. In this study, uniaxial compression tests are conducted in combination with Digital Image Correlation （DIC） technology to investigate the failure characteristics of specimens with different borehole sealing materials. The tests are performed using a DNS200 electronic universal testing machine on four types of specimens: intact specimens, specimens with holes, specimens filled with polyurethane material, and specimens filled with CF-2 expanding material. The stress-strain behavior, fracture propagation processes, and displacement changes around the hole are monitored in real time. The results show that the failure process of intact specimens and specimens filled with CF-2 expanding material is consistent, characterized by compaction, elastic, elastoplastic, and post-peak stages. In contrast, specimens with holes but without filling and those filled with polyurethane material exhibit a longer compaction stage and greater initial strain due to their lower material strength. The fracture propagation patterns indicate that fractures in specimens with holes mainly extend along the hole periphery, accompanied by axial through-fractures. The failure mode gradually shifts from axial compression to tensile and shear failure. The strength of the sealing material significantly affects the displacement around the hole. The radial deformation at the upper and lower ends of the borehole filled with CF-2 expanding material and polyurethane sealing material is 1.66 mm and 2.26 mm, respectively. The circumferential displacement at the top of the borehole filled with polyurethane material is 5.5 times that of the borehole filled with CF-2 expanding material. High-strength sealing materials （such as CF-2 expanding material） can effectively reduce the deformation of the upper and lower ends of the borehole, thereby enhancing the stability of the borehole. By comparing the failure characteristics and fracture propagation patterns of different specimens, the study reveals the failure mechanism of the gas drainage borehole sealing section and clarifies the critical role of sealing material strength in borehole stability. High-strength sealed materials can significantly enhance the stability of the borehole sealed section, reduce fracture propagation, and lower the risk of gas leakage. This research provides a theoretical basis for optimizing gas drainage borehole design and selecting appropriate sealing materials, and offers important guidance for improving gas drainage efficiency and ensuring mine safety.