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Slope stability design is commonly evaluated using limit equilibrium methods such as Bishop’s Method of Slices. The approach is to calculate the driving and resisting forces along a circular (or log-spiral) slip surface and determine the factor of safety against rotation or movement. The location of the slip surface (circular or log-spiral) is commonly utilized to define three failure regimes:

1. Internal – failure surfaces that are contained entirely within the reinforced soil zone
2. Compound – failure surfaces that begin outside or behind the reinforce soil zone but pass through the reinforcement and exit in the foundation or through the structure face
3. Global – overall/deep seated failure surfaces that pass outside the reinforcement and into the underlying foundation soils

Regardless of the failure regime, the designer must analyze numerous failure surfaces and isolate that surface which generates the least factor of safety for stability.

Computer software allows the designer to rapidly analyze thousands of failure surfaces and optimize reinforcement requirements to provide adequate factors of safety at the best economics. For each failure surface passing through a layer of reinforcement, the analysis considers the tensile strength of the reinforcement to investigate tensile rupture or failure, and geogrid pullout resistance.

Strata makes available to the designer tools that allow easy selection of primary and secondary reinforcements. StrataSlope Software is a limit- equilibrium design package that automates primary geogrid reinforcement design utilizing circular or log-spiral failure surfaces with the Bishop’s Method of Slices. Additional tools are available that address surficial stability using parallel failure surface of infinite length (i.e. sliding wedge approach).

Project Donzi Landfill Atlanta, Georgia Structure Height 26 ft (max.) Slope Angle 1H:2V; 1H:1V Area 120,000 SF Primary Geogrid Stratagrid SG500, SG550 Facing 90-deg. welded-wire form with secondary geogrid wrap and gravel fill

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