Estimate of Safe Angle for Cut Slopes Under Different Geology and Rainfall Intensity in Central Nepal

Abstract

This research has been carried out on a cut slope of Kathmandu-Terai Fast Track Road near Koppugaon located at Dakshinkali Municipality, Kathmandu. The cutting of the slope without considering the possible effects of geological parameters of slope material may cause unexpected slope failures which may cause loss of lives and properties. This research deals with the effects of rainfall and groundwater conditions on the stability of the cut slope. The cut slope made up of fluvial-lacustrine gravelly soil deposits of Lesser Himalaya is modeled as a finite slope using Limit Equilibrium and Finite Element analysis. The global stability analysis of the slope has been carried out by using Slope/W software, whereas the effects of rainfall (i.e. the fluctuation of groundwater, moisture content, saturated water content, volumetric water content, changes in pore water pressure, and hydraulic conductivity) are analyzed by using Seep/W Software. The slope stability analysis of the cut slope has been carried out without and with the consideration of the effects of rainfall for different angles of inclination of the slope and the safe angle for an FOS >=1.5 for the slope is calculated. The result of the stability analysis of the slope shows that the safe cut slope angle for the slope under consideration is about 48 degrees in dry conditions and 42 degrees in wet conditions which will result in a factor of safety of more than 1.5.