Stability, Erosion, and Morphology Considerations for Sustainable Slope Design

The construction of more natural and sustainable earth slopes requires the consideration of erosion and runoff characteristics as an integral part of the design. These effects not only result in high costs for removal of sediment, but also a profound damage to the ecosystem. In this dissertation, innovative techniques are developed such that more natural appearing slopes can be designed to minimize sediment delivery, while meeting mechanical equilibrium requirements. This was accomplished by: a) examining the fundamental failure modes of slopes built with minimum compaction (FRA) to enhance quick establishment of forest, b) investigating the geomechanical and erosion stability of concave slopes, and c) developing design equations for a new type of inclined-face retaining structure, the Piling Framed Retaining Wall (PFRW), which in the limit is a confined slope. The analysis of several potential failures via Limit Equilibrium (LEM) and Finite Element (FEM) suggested that the governing failure of FRA slopes is shallow and well represented by infinite slope conditions, and laboratory and field data suggests that seasonal increase of stability due to matric suction is possible, while instability may occur under local seismicity. The investigation of the mechanical and erosion stability of concave slopes began with a mathematical definition of critical concave slopes at limiting equilibrium. Based on this, a mechanism to design concave slopes for a selected Factor of Safety (FS) was proposed. Results indicated that concave slopes can yield 15-40% less sediment than planar slopes of equal FS, and the stability is not compromised by errors in the construction. Concave slopes satisfying mechanical equilibrium are not necessarily in erosion equilibrium as observed in many natural landscapes. It was shown that when these two equilibrium conditions are met, the slopes become sustainable and a set of equations describing sustainable concave slopes was proposed. Finally, rational design equations for the innovative PFRW were developed based on numerous FEM analyses for different soil and geometry conditions. The equations provided a good prediction of the soil stresses measured on a PFRW built in Knoxville, TN.