Hydration induced fracture growth and strength reduction in miocene shale with implications for slope stability

Shale constitutes a significant portion of exposed sedimentary rock, necessitating an understanding of its response to various geo-environmental conditions. In southeastern Bangladesh, the prevalence of Miocene shale, particularly in road cut sections, raises concerns regarding slope stability during the rainy season. This study investigates the influence of loosely packed silt layers within the silt-clay matrix of Miocene shale on its deformation behavior and mechanical properties when subjected to hydration. This study investigates the deformation behavior and mechanical properties of shale influenced by silt layer orientations and hydration levels. Laboratory experiments revealed that silt interlayers significantly affect fracture formation during water immersion, demonstrating shale’s sensitivity to aquatic environments. Notably, fractures initiated within minutes of immersion, with their development intricately linked to the orientation of silt layers. The analysis of deformational responses under stress highlighted that different silt layer configurations lead to varied fracture mechanisms, emphasizing the complex interplay between structural orientation and material behavior. Fractures in shale develop within 2 to 15 min of water immersion, highlighting the material’s sensitivity to aquatic conditions. The orientation of silt layers significantly influences the growth of these fractures in water, while hydration is shown to reduce shale strength by 86–87%, which has a considerable impact on stability. The hydration level and strength reduction were investigated and a 3.5% hydration level results in an 80% loss of strength in shale. Furthermore, elastoplastic analysis suggests that such a reduction in strength may lead to slope failure, underscoring the critical relationship between hydration, silt layer orientation, and the mechanical integrity of shale. These findings underscore the importance of considering both hydration and silt layer orientation in assessing shale behavior, particularly in geotechnical applications where water exposure is critical.