Filled Joint Defects Shape Rock Deformation Around Underground Circular Openings

Biaxial compression tests under low lateral confinement reveal that the geometric configuration of through-going filled fissures strongly dictates load-bearing capacity, deformation localization, and failure evolution around circular underground openings. Investigating how surrounding sandstone behaves when an opening coexists with a filled weak discontinuity, researchers tested two single-factor experimental series alongside intact and single-hole reference groups. The first test series evaluated fissure inclinations of 10°, 15°, and 20° at a constant filling thickness of 2 mm, while the second examined filling thicknesses of 2, 5, and 10 mm at a constant inclination of 15°.

The core methodological contribution of the investigation centered on simultaneously characterizing the global mechanical response, local deformation at the roof and floor of the circular hole, acoustic emission (AE) activity, and the evolution of tensile–shear AE sources. By combining these measurement streams, the experimental setup established direct empirical links between defect geometry, overall load-bearing performance, and localized structural instability in the surrounding rock mass.

Mechanical testing demonstrated that fissure geometry heavily influenced peak compressive strength and the timing of localized failure. For specimens tested at a 15° fissure inclination, measured peak strengths reached 43.16 MPa for a 2 mm filling thickness, 48.96 MPa for a 5 mm thickness, and 47.90 MPa for a 10 mm thickness. In comparison, tests conducted at a constant 2 mm filling thickness produced peak strengths of 53.47 MPa at a 10° inclination, 43.16 MPa at 15°, and 55.61 MPa at 20°. The specimen combining a 15° inclination with a 2 mm filling thickness, designated s-15-2, developed the largest local deformation concentration and the earliest local instability around the circular hole. In contrast, the specimen with a 15° inclination and a 5 mm filling thickness (s-15-5) achieved a relatively high peak strength, delayed roof instability, and restricted floor deformation.

Monitoring acoustic emissions demonstrated that joint thickness shifts the underlying damage process toward interfacial sliding. Increasing the filling thickness markedly elevated middle-to-late-stage AE activity, with shear-type AE event proportions reaching 67.5% under the 5 mm condition and 63.9% under the 10 mm condition. These shifts indicate that thicker filled discontinuities increasingly govern rock degradation through shear-related sliding along interfaces. Overall, the findings differentiate the separate influences of hole-induced stress concentration and filled-fissure geometry on load-bearing limits, deformation localization, and AE-source transitions, offering an experimental foundation for identifying unstable zones around openings adjacent to filled weak discontinuities.

Subject of Research: Rock mechanics and deformation around underground openings with filled joints

Article Title: Effects of persistent joints on the strain failure of the roof and floor around a circular opening

Article References: Deng, H., Shen, J., Xu, J., & Liu, Y. (2026). Effects of persistent joints on the strain failure of the roof and floor around a circular opening. Discover Applied Sciences. https://doi.org/10.1007/s42452-026-09854-w

Image Credits: AI Generated

DOI: 10.1007/s42452-026-09854-w

Keywords: rock mechanics, underground openings, persistent joints, sandstone deformation, acoustic emission, biaxial compression, shear failure, structural stability, Effects, persistent, joints, strain