Weathering-induced damage factor for deterministic stability assessment of andesitic rock slopes

Weathering significantly degrades the mechanical properties of rock materials and discontinuities, thereby affecting slope stability. Nevertheless, its influence has not been quantitatively integrated into deterministic stability analyses of discontinuity-controlled failures. This study addresses this gap by introducing a weathering-induced damage factor defined using continuum damage mechanics based on the elastic modulus. Field investigations and laboratory tests were conducted on five slopes within four abandoned quarries in İzmir, Türkiye. Kinematic and limit equilibrium analyses were performed to identify failure modes and factor of safety (FoS) values. In-situ tilt tests were also carried out to assess shear strength variations under different weathering conditions. The results show that shear strength decreases with increasing weathering, and cooling joints generally exhibit lower friction angles than flow bands. While undulation angles vary with discontinuity type, they are not influenced by weathering. Discontinuity spacing also shows no significant variation. Regression analyses indicate that the damage factor can be reliably estimated from the friction angle of discontinuities and uniaxial compressive strength. Sensitivity analyses reveal that slope geometry is the most influential parameter across different quarries, whereas the damage factor becomes more significant within a single quarry. The proposed framework is validated using thirteen documented case studies, which demonstrate consistent relationships between the damage factor and FoS for varying weathering degrees. Rather than homogenizing mechanical parameters across a slope with heterogeneous weathering, this study offers a practical and scalable method to incorporate weathering-induced damage into the stability assessment of andesitic rock slopes, specifically for toppling and planar failures.