The influence of joints and bedding planes on the slope stability: case studies from highly fractured basement terrains and sandstone sedimentary rocks

The stability of slopes strongly influences discontinuities in structurally complex terrains, particularly joints and bedding planes. This study investigates the role of structural anisotropy in slope instability through two case studies: (1) sandstone-dominated sedimentary sequences in northern Sudan, where the bedding planes present potential failure surfaces in both field and laboratory measurements, and (2) highly fractured basement rocks in the Red Sea Hills northeast of Sudan, where dense joint networks and foliations control slope failures. In basement complex rocks, four types of rock failure were identified: plane, toppling, wedge, and circular failures. In contrast, in sedimentary sequences, bedding plane orientation significantly affects the likelihood of plane, and toppling failures. Field observations and geomechanical analyses are used to measure rock mass properties. Results indicate higher compressive strength when the load direction is perpendicular (beta = 90) or parallel (beta = 0) to bedding planes, and lower values when inclined (beta = 45). The findings underline the importance of discontinuities in slope stability assessments, particularly in fields where anisotropy plays a primary role on failure mechanisms.