## 4 Conclusions  
(1) Confining pressure is a critical factor in the failure of red sandstone. At low pressures, tensile failure is the predominant mode. Throughout the loading process, numerous damaged areas emerge within the specimen. As the load increases, insufficient confining pressure leads to the development of complex, irregularly shaped macro-cracks in most damaged areas. Eventually, these macro-cracks and micro-cracks interconnect to form a complex network. As confining pressure increases, shear failure supersedes tensile failure. This strong inhibition restricts the expansion of damaged areas, enhances rock flexibility, reduces the number of prominent cracks, decreases the overall degree of fragmentation, and reflects an increased bearing capacity.  
(2) Rock failure is influenced by the effective intermediate stress, \(\sigma_{2}\), on the failure surface. Rock deformation exhibits axial compression and dilation along the direction of minimum principal stress. At peak strength, the deformation of the specimen aligns parallel to the \(\sigma_{2}\) direction, forming a shear failure surface at an angle, typically greater than \(45^{\circ}\), relative to the \(\sigma_{3}\) direction. This angle increases with \(\sigma_{2}\), enhancing the ductility of rock  
Figure 12: Failure pattern of red sandstone sample: (a) 600 m buried depth; (b) 1000 m buried depth; (c) 1400 m buried depth.  
failure. This behavior results from stress concentration at the tip of large cracks and a stress differential across the specimen, akin to shear loading. At low confining pressures, the rock's strength and its resistance to direct shear deformation are compromised, resulting in a combination of direct and oblique shear failures. With increased confining pressure, the specimen's strength and resistance improve, primarily exhibiting oblique shear failure.  
(3) The peak of acoustic emission ring counts in sandstone under varying confining pressures occurs slightly after the macroscopic failure of rock samples. This suggests that confining pressure mitigates the failure of rock particles and the sliding of cracks, enhancing not only the shear failure strength but also the post-peak bearing capacity of rock samples. Additionally, intense acoustic emissions related to these conditions promote the fracturing of rock samples, resulting in an overall delay in the failure process.  
(4) In sandstone samples, the crack morphology shifts from tensile to shear with increasing depth. Shear cracks, characterized by easy initiation, long propagation distances, and rapid spread, are the primary factors in the formation of water inrush channels and are critical in the occurrence of water inrush accidents.  
Conceptualization, S.S. and S.Z.; software, X.H.; validation, S.S.; formal analysis, S.Z.; investigation, S.Z.; resources, X.H.; data curation, S.S.; writing--original draft preparation, S.Z.; writing--review and editing, X.H.; visualization, X.H.; supervision, S.Z.; project administration, S.Z.; funding acquisition, S.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Open Fund of State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, grant number GJNY-20-113-19, the National Natural Science Foundation of China, grant numbers 51974173 and 52004147, and the Natural Science Foundation of Shandong Province, grant number ZR2020 QE129.  
Not applicable.  
The data used to support the findings of this study are available from the corresponding author upon request.  
Thank you to [PERSON] from State Power Investment Corporation Limited for conceptualizing, preparing the initial draft, and managing the data for this paper.  
The authors declare no conflict of interest.