International Journal of Mining and Geo-Engineering

International Journal of Mining and Geo-Engineering

Coupled effects of joint surface roughness, infill thickness, and orientation on the triaxial strength of jointed rock: experimental insights for refining Jaeger’s failure criterion

Document Type : Research Paper

Authors
1 Department of Mining Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran
2 Department of Mining Engineering, Urmia University, Urmia, Iran
10.22059/ijmge.2026.416174.595391
Abstract
The mechanical response of infilled rock joints under triaxial compression is governed by joint roughness, infill material thickness (IMT), and joint orientation. Although the influence of these parameters has been studied individually, their interactive effects on strength anisotropy and failure evolution remain underexplored. In this study, 270 triaxial compression tests were conducted on limestone specimens containing tooth-shaped asperity (TSA) and rough undulating (RU) joints with IMTs of 3, 5, and 8 mm and joint orientations (α) of 0°, 30°, 45°, 60°, and 90°. Artificial joints were fabricated using high-pressure water jet cutting to ensure accurate, repeatable joint geometries. The results indicate that joint orientation exerts the strongest influence on axial strength (σ1), with the lowest strength consistently occurring at α = 60°. In contrast, the highest strengths were obtained at α = 0° and 90°, where failure was governed primarily by the intact rock matrix. Under identical testing conditions, TSA specimens exhibited greater strength than RU specimens, demonstrating that asperity interlocking contributes to load-bearing capacity. An increase in IMT from 3 mm to 8 mm resulted in a progressive reduction in σ1. This was accompanied by a transition in failure behavior from interface-controlled shearing to deformation and sliding within the infill layer. Experimental observations were further evaluated against predictions of the Jaeger failure criterion. The comparison showed that the criterion tends to overpredict σ1 at intermediate joint orientations and low confining pressures, whereas it achieves considerably better agreement at α = 60° and under higher confinement levels. The results demonstrate the limitations of conventional analytical approaches for representing rough infilled joints and provide experimental evidence to improve failure criteria for jointed rock masses. The outcomes of this study contribute to a better understanding of rock mass stability and support more reliable numerical and engineering assessments of surface and underground excavations.
Keywords
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