Stability Assessment of Block–Flexural Toppling Using Numerical and Deterministic Approaches

Summary

Abstract

Block–flexural toppling is a complex failure mechanism commonly observed in jointed rock slopes, resulting from the combined effects of block rotation and flexural deformation. This instability is primarily controlled by geological structures, particularly the orientation, persistence, and mechanical properties of discontinuities. This study presents a stability assessment of block–flexural toppling at Cliff 05, Citatah, West Bandung Regency, West Java, Indonesia, where recurrent rock block detachments have been documented. The slope is dominated by a primary joint set that is nearly perpendicular to the slope face and intersected by a secondary joint set, creating conditions favourable for toppling failure. To investigate the failure mechanism, stability analyses were conducted using both numerical modelling and the Limit Equilibrium Method (LEM). Numerical simulations were performed using the finite element method within an elastic–plastic framework, while LEM was applied to evaluate the factor of safety under varying geometric and mechanical conditions. Rock mass and discontinuity parameters were derived from field observations and rock mass classification systems, including the Rock Mass Rating (RMR) and Geological Strength Index (GSI). Joint shear strength parameters were estimated using the Barton–Bandis criterion for both joint sets. The joint network was represented using deterministic and statistical approaches. Results from numerical modelling indicate total displacements ranging from approximately 9.5 to 19 mm, with plastic zones developing around surface joints and joint intersections. LEM analysis shows a reduction in factor of safety consistent with increasing slope inclination and unfavorable joint orientations. Sensitivity analysis identifies internal friction angle, slope inclination, and slope face angle as the most influential parameters governing block–flexural toppling stability. The comparative results highlight the advantages and limitations of each method in assessing toppling-prone rock slopes.