Exploring the shear behavior and local roughness degradation of rock fractures with laterally composite dentate profiles

Abstract

The shear mechanical properties of natural rock fracture play a vital role in resolving complex geotechnical engineering issues. Existing two-dimensional (2D) fracture models fail to capture spatial asperity distribution, while natural three-dimensional (3D) fractures are too random for systematic analysis. To address this, five composite fracture surface models, derived from single-angle dentate profiles, were proposed to represent the spatial characteristics of roughness. Using 3D printed molds, rock-like mortar specimens were fabricated for direct shear testing. Shear behaviors and progressive roughness degradation were quantitatively examined via 3D scanning and the indicator θ*max/(C + 1). Results demonstrate that spatial roughness gradients govern the progressive failure of asperities and the transition from sliding to shearing. Quantitatively, the peak shear strength increases significantly from 1.82 MPa to 14.57 MPa under normal stresses ranging from 2 MPa to 8 MPa. Moreover, the overall roughness reduction exhibits a strong linear correlation with the shear strength, yielding high determination coefficients from 0.805 to 0.942. For practical engineering applications, it is highly recommended to evaluate fracture shear capacity based on the collaborative load transfer of spatially distributed asperities rather than isolated local peaks. These findings provide a vital experimental basis to optimize shear strength models for naturally rough rock fractures.