Simplified methods for evaluating road prism stability

Mass failure is one of the most common failures of low-volume roads in mountainous terrain. Current methods for evaluating stability of these roads require a geotechnical specialist. A stability analysis program, XSTABL, was used to estimate the stability of 3,696 combinations of road geometry, soil, and groundwater conditions. A sensitivity analysis was carried out to find the most important site-specific variables in estimating slope stability, and two regression equations were developed to predict the factor of safety (FS) for a given road, one with the groundwater below the road fill and one with the groundwater in the road fill. The resulting equations predicted failures on road segments where failures were observed to have occurred. A comparison of the predicted FSs from the regression equations with the FS values predicted by the infinite slope equation showed that both methods predicted similar FSs.