Slope Stability Analysis of Steep-Reinforced Soil Slopes Using Finite Element Method

Recently, use of geosynthetics has gained widespread popularity and has been increasingly used as reinforcing element in several engineering practices of earth retention structures like reinforced earth walls, reinforced slopes, etc. Often the required soil type of requisite characteristic soil properties considered for design are not available locally, hence the available soil type has to be used. With that under consideration, this study deals with the analysis of a steep soil slope embankment reinforced with geogrids under different soil backfill properties. The steep slope is basically designed to widen and elevate the existing natural ground in order to provide road pavement over it. Initial design consideration included conventional limit equilibrium method along with classical earth pressure theories. The design is further modeled and analyzed meticulously according to the staged construction sequence undertaken at site, in a geotechnical finite element analysis software, i.e., PLAXIS. This study mainly investigates the effects of use of different types of soil backfill on stability of slope. Effect of variation of soil parameters, i.e., cohesion and angle of internal friction on steep slope embankments of different heights (6, 12, 18, 24, and 30 m) are studied through this analysis. Since very steep and very high slope embankments were considered for the study, tiered structure, i.e., provision of berm was considered. The effect of width of berm was also considered as a parameter and corresponding effect on the stability of slope was studied. The observed trends of results were further compared with available literatures and previous studies. The results suggested that with increase in soil parameters like cohesion (c′) and angle of internal friction (Φ) the factor of safety for the global stability further increased. From the study it was observed that the most optimum soil type was found to be the soil with low cohesion and high angle of internal friction, because upon increasing the cohesion of soil, although increase in global stability was observed, it also led to increase in horizontal displacements and axial forces acting over the geogrids. From the results it was also observed that use of tiered structure or provision of berm increased the factor of safety for global stability marginally and reduced the forces and horizontal displacements significantly on the lower tier. It was concluded that in case of non-availability of recommended granular soil, the available soil fill be utilized only for low height embankments. For high embankments, only recommended granular soils should to be used.