Microstructural and mechanical behavior of conglomerate in interbedded rock slopes: Insights into microscopic complexity and fracture mechanism

Abstract

The microstructural and mechanical behavior of conglomerate rock in interbedded sedimentary slopes is critically influenced by intrinsic heterogeneity, including varied clast sizes, weak cementation, and discontinuous matrix fabrics that form mechanically weak zones. This study integrates mineralogical, microstructural, and mechanical analyses to investigate degradation behavior and its implications for slope stability. Petrographic and SEM-EDS analyses reveal that mineralogical variation, particularly the kaolinite/muscovite ratio, concentrates stress at clast-matrix interfaces, promoting fracture initiation. X-ray micro-CT imaging and pore network modeling expose internal fabric irregularities, grain clustering, and potential fracture pathways. Cyclic wetting and drying induce microstructural deterioration, with the wet–dry deviation of unit weight increasing from 1.15 % to 1.87 %, accompanied by stiffness loss and increased brittleness. Shear and elastic moduli increase on average by 69.6 % and 22.5 %, respectively, indicating evolving mechanical behavior. Finite element analysis confirms that reduced stiffness lowers the critical Strength Reduction Factor (SRF) by 8.5 %, compromising slope stability. A 5 % decline in the shear-to-elastic modulus ratio (G/E) and a reduced Poisson's ratio further reflect microcrack propagation and mineral alteration. Connected porosity increases by 15.9 %, indicating the development of fracture connectivity. The estimated Joint Roughness Coefficient (JRC), ranging from 12 to 14 via X-ray micro-CT, aligns with naturally generated fractures, validating surface roughness characteristics. These multi-scale results offer mechanistic insights into the weakening behavior of conglomerates, improving durability assessments and enhancing the reliability of geomechanical models for slope stability prediction in interbedded sedimentary environments.