Fracture-induced variations in mechanical properties of silty mudstone under triaxial stress

This study aims to examine the impact of pre-existing fractures on the mechanical response of silty mudstone. A series of laboratory-scale triaxial compression tests were conducted on both intact and fractured rock specimens with varying fracture angles (theta) and connectivity ratios (k), corresponding mechanical properties, energy evolution, and failure mode were comprehensively analyzed under varying loading rates and confining pressure (sigma 3). Results demonstrated that increased loading rates enhanced peak strength and elastic modulus, transitioning from ductile to brittle behavior, accompanied by shear-to-composite failure. Higher sigma 3 extended the plastic deformation and effectively improved the structural strength and stiffness, although peak strength sensitivity decreases at higher sigma 3. Fractured specimens exhibited reduced strength and stiffness compared to intact specimens, primarily attributed to cohesion loss rather than changes in internal friction angle. However, increasing sigma 3 effectively mitigated fracture-induced mechanical degradation. The energy evolution of rock specimens indicates that total energy density (TED), elastic energy density (EED), and dissipated energy density (DED) exhibit distinct variations governed by sigma 3, theta, and k, and the presence of fractures have a certain influence on energy accumulation and dissipation behavior, as reflected by decreased EED and increased DED associated with crack propagation. Furthermore, larger theta promoted tensile-dominated failure, while increased k exacerbated localized stress concentrations and intensified microcrack interactions, transitioning failure from combined tension-shear to tensile mechanisms, both of which provoked more severe damage in rock specimens. The results found in this study offer a reference for the further examination of fractured rock and numerical model calibration.