Slope Stability Evaluation of Highway Embankments in Large Transportation Projects

Construction of large highways often involves raising the elevation of existing ground to build the planned highway subgrade. As a result, borrow materials are typically placed to form embankments with different heights and slope inclinations. Often times factors such as different embankment heights, different slope inclinations, and variable subsurface conditions in long highway alignments can make the selection of the most critical cross sections in terms of slope stability analysis a tedious task. As an example, the cross section with the largest embankment height may not be the most critical case to analyze if it is proposed to be founded on a very dense subsurface soil. To identify the cross sections prone to potential global slope stability failures when designing embankments, a soil strength parametric study was performed for different embankment heights in drained and undrained conditions. The results of the analyses and parametric study were used to determine the critical condition and develop equations and tables correlating the minimum allowable shear strength of the soil to the height of the proposed embankment. The suggested equations and tables are useful tools to predict the sections with potential failure along highway alignments in the preliminary slope stability analysis process. The equations are compatible to both allowable strength design (ASD) and load resistance factor design (LRFD) slope stability analyses.