Design of Geogrid Reinforced Earth Walls: Transition of Limits and Critical Surfaces

The majority of design approaches or methodologies for reinforced earth walls or slopes are based on separately investigating the internal and external stabilities of the system. The internal stability is examined by satisfying the local stability of reinforcements at each level based on the predetermined critical slip plane (line of maximums) and the tributary area of each reinforcing layer. Recent research aimed at incorporating the contributions of the various elements of reinforced earth walls, some of which are mostly based on statistical correlations. The German code of practice for design/analysis of reinforced earth walls and slopes offers slightly different methodology for analyzing the internal stability of the reinforcement. It is mainly based on investigating numerous circular and random slip surfaces, within and beyond the reinforcement zone (internal and external), while accommodating the axial (resistance) forces provided by all reinforcement layers intercepting these surfaces. This paper presents some of the technical and design considerations and possible improvements on design methodology for reinforced soil walls and slopes. Of particular interest is the use of the apparent cohesion concept in the design of geosynthetic reinforced soil systems and the transition of limit equilibrium states (mobilization of actual state of equilibrium critical surfaces instead of the presumed or predefined most critical surface) for reinforced earth walls. The equivalent cohesion concept was used to transform reinforced soil masses into equivalent cohesive soil masses with friction capacity. Cases of analyses with comparisons between reinforced soil walls and the equivalent cohesive masses were performed and the results revealed very similar results between the two systems in terms of the safety of the walls