Towards a Rock-type Specific Brittle Hoek-Brown failure constant “s” Matrix Based on Standard Uniaxial Compression Tests

Abstract

Accurate prediction of excavation stability in rockmasses is a critical requirement in underground mining and civil engineering excavation design. The Hoek-Brown failure criterion is one of the most widely used empirical methods in rock mechanics for predicting the performance of excavations in rocks. The Hoek-Brown failure criterion has undergone significant improvements based on experience gained in its use since its introduction. The most significant development of the generalized Hoek-Failure criterion was the introduction of the Brittle Hoek Brown failure criterion commonly known as the m-zero damage initiation criterion by Martin (1993) who concluded that for rockmasses with Geological Strength Index of about 65 and greater the frictional constant “m” plays little role in the failure process and that the cohesion constant “s” is about 0.11 independent of the rock type. Suorineni and Kaiser (2002) and Suorineni et al. (2009) argued that “s” should not be constant for all rock types but based on their genesis, composition and texture. Following this, Suorineni et al. (2009) provided a comprehensive methodology for determining “s” for specific rock types. This study contributes to the development of matrix of rock types and their corresponding cohesion constants “s” similar to the rock type-𝑚𝑖 matrix by Hoek (1997). To date several rock types have been tested from Canada, Australia and Kazakhstan. The results confirm that indeed it is more appropriate to determine rock-type specific “s” for use in the brittle Hoek-Brown damage initiation criterion for a more reliable assessment of underground structures in rocks. This is significant in the evaluation of the performance of excavations and pillars in rocks and in the estimations of tendon ground support lengths based on depth of failure chart for which the “s” value is a critical parameter. Based on these findings, it is recommended that future research maximize core sample volumes per lithology to mitigate statistical skew caused by intrinsic rock heterogeneity and potential data loss from technical equipment limitations. Furthermore, researchers should prioritize freshly drilled core samples to avoid mechanical artifacts associated with long-term storage and utilize non-destructive P-wave velocity screening to ensure specimen integrity. Finally, integrating advanced analytical techniques such as SEM and XRD is essential to establish rigorous mathematical correlations between micromechanical mineralogical fabrics and the macro-scale cohesive constant “s”