A simplified approach to determine the unique direction of sliding in 3D slopes

• A simplified approach based on Spencer's method to determine the direction of sliding in 3D slopes.
• A unique direction of sliding is involved to calculate the factor of safety.
• The direction of sliding has significant effects on stability of asymmetrical slopes.

Based on the Spencer's method, this paper presents a simplified approach to assess the stability of three-dimensional (3D) asymmetrical slopes. The approach allows for satisfaction of the force equilibrium in all three directions and the moment equilibrium about two co-ordinate axes. A unique direction of sliding is involved here to calculate the factor of safety. The direction of sliding (DOS) is always parallel to the plane of symmetry for symmetrical slopes. However, the DOS in asymmetrical slopes could deviate from the symmetrical plane and affect the stability assessments. Through two simple asymmetrical examples, the calculated results demonstrate that the deviation of the sliding from the symmetry could destabilize the slopes and cause failures. Neglecting the DOS in 3D asymmetrical slopes will overestimate their stability. Application of the presented approach into complex asymmetrical problems is straightforward.