Wedge Slope Failure of Natural Sedimentary Rock Formation Based on Weathering Potential

Weathering and durability play important roles in the instability condition of sedimentary rock formation. Weathering and durability are not only quite dependent on the other characteristics of unweathered sedimentary but also the interbedded sequence of shear strength with the other rock types. This study aims to evaluate the potential failure of sedimentary rock slopes in Batu City, Indonesia, by analyzing weathering and durability characteristics. Slope stability analysis uses a kinematical approach because this approach considers the equilibrium of forces acting on all rigid blocks as in the traditional slice methods. The stereography graphical model in the kinematic analysis showed probable slope sliding potential due to the wedge failure during the rainy season. Laboratory physical properties classified the sedimentary rock layers as lapilli tuff breccia, breccia claystone, tuff claystone, and breccia. Mechanical strength properties produced compression stress between 2.5 to 13.2 MPa. The result shows that the factor of safety (FS) obtained at 1.25 can be classified as a level of susceptibility and an infeasible condition. Generally, a large safety factor value of 1.50 can be assumed for permanent rock slopes. Shear strength behaviour indicated many influences of weathering and durability factors and could be included in low to high strength levels.