DU Shaohua, MA Jinyin, MA Liyao, ZHAO Yaqian. 2024: Unconfined compressive strength and failure behaviour of completely weathered granite from a fault zone. Journal of Mountain Science, 21(6): 2140-2158. DOI: 10.1007/s11629-024-8698-5
Citation: DU Shaohua, MA Jinyin, MA Liyao, ZHAO Yaqian. 2024: Unconfined compressive strength and failure behaviour of completely weathered granite from a fault zone. Journal of Mountain Science, 21(6): 2140-2158. DOI: 10.1007/s11629-024-8698-5

Unconfined compressive strength and failure behaviour of completely weathered granite from a fault zone

  • Understanding the strength characteristics and deformation behaviour of the tunnel surrounding rock in a fault zone is significant for tunnel stability evaluation. In this study, a series of unconfined compression tests were conducted to investigate the mechanical characteristics and failure behaviour of completely weathered granite (CWG) from a fault zone, considering with height-diameter (h/d) ratio, dry densities (ρd) and moisture contents (ω). Based on the experimental results, a regression mathematical model of unconfined compressive strength (UCS) for CWG was developed using the Multiple Nonlinear Regression method (MNLR). The research results indicated that the UCS of the specimen with a h/d ratio of 0.6 decreased with the increase of ω. When the h/d ratio increased to 1.0, the UCS increased ω with up to 10.5% and then decreased. Increasing ρd is conducive to the improvement of the UCS at any ω. The deformation and rupture process as well as final failure modes of the specimen are controlled by h/d ratio, ρd and ω, and the h/d ratio is the dominant factor affecting the final failure mode, followed by ω and ρd. The specimens with different h/d ratio exhibited completely different fracture mode, i.e., typical splitting failure (h/d=0.6) and shear failure (h/d=1.0). By comparing the experimental results, this regression model for predicting UCS is accurate and reliable, and the h/d ratio is the dominant factor affecting the UCS of CWG, followed by ρd and then ω. These findings provide important references for maintenance of the tunnel crossing other fault fractured zones, especially at low confining pressure or unconfined condition.
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