A Simplified Approach for Evaluating 3D Slot-Cut Slope Stability

Abstract

Slot-cut excavations have been widely used to maintain stable slopes during excavation adjacent to structures or at the toe of steep slopes. It is well known that the increased stability in slot-cut excavation is due to the contribution of out-of-plane resistance or the three-dimensional (3D) effect on slope stability. The evaluation of slot-cut stability in practice, however, is often based on a highly simplified single-block wedge analysis valid only for simple slope geometry and homogeneous soil conditions. This paper presents a more rigorous approach for slot-cut stability analysis that is applicable for slopes even with complicated geometry, stratigraphy, and surcharge loading conditions. The approach considers the 3D effect by incorporating side-panel shear resistance in the force limit-equilibrium equations. A formulation is derived for a multiple-slice failure wedge, which can be conveniently implemented using a spreadsheet, combined with a two-dimensional (2D) limit-equilibrium slope stability analysis. The input for the critical 3D multiple-slice failure wedge is obtained from the output of the 2D stability analysis. In this approach, the slot-cut excavation sequence can be simply simulated and different combinations of cut depth and width can be compared. This approach is demonstrated by successful application of slot-cut construction for removal and repair of a landslide below an existing residence. This can be readily applied to other applications in which the contribution of 3D effects is considered critical in demonstrating adequate stability in temporary excavations.