Geosynthetic Reinforced Multitiered Walls

Current design of mechanically stabilized earth (MSE) walls shows that the tensile stress in the reinforcement increases rapidly with height. To take advantage of both the aesthetics and the economics of MSE walls while considering high heights, multitiered walls are often used. In such walls, an offset between adjacent tiers is used. If the offset is large enough, the tensile stress in the reinforcement in lower tiers is reduced. However, a rational design methodology for multitiered MSE walls that accurately predicts wall performance is lacking. AASHTO 98 design guidelines are limited to two-tiered walls with zero batter. In fact, this design is purely empirical using “calibrated” lateral earth pressures adopted from limited guidelines developed for metallic strip walls. Empirical data available for multitiered walls is limited and it seems to be nonexistent for geosynthetic walls. In fact, generation of an extensive database for tiered walls is a major challenge since there are practically limitless configurations for such systems. As an alternative, this study presents the results of parametric studies conducted in parallel using two independent types of analyses: One is based on limiting equilibrium (LE) and one on continuum mechanics. The premise of this work is that if the two uncoupled analyses produce similar results, an acceptable level of confidence in the results can be afforded. This confidence stems from the fact that LE is currently being used for design of reinforced and unreinforced slopes (i.e., having a slope angle less than 70°); the agreement with continuum mechanics facilitates its extrapolation to use in MSE walls. Parametric studies were carried out to assess the required tensile strength as a function of reinforcement length and stiffness, offset distance, the fill and foundation strength, water, surcharge, and number of tiers. It is concluded that LE analyses may be extended to the analysis of multitiered walls.