Internal Compound Stability
Wall designs have typically been limited to internal stability, external stability and bearing analysis by the site civil engineer or the wall design engineer. Additionally, the overall stability of the site is the responsibility of the owner and should be addressed by the owner, by contracting with a geotechnical engineering firm. The geotechnical engineering firm should provide a full global analysis of the entire site including the effects of the segmental retaining walls.
As the design roles become more defined it has become more customary for an Internal Compound Stability (ICS) analysis to be performed. ICS calculations determine the factors of safety for potential slip surfaces which pass through the unreinforced retained soil, the reinforced soil mass and the wall facing within the wall design envelope.
Internal compound stability calculations are limited to a wall design envelope above the base material and back no further than 2 (H) or He + L, whichever is greater. This evaluation zone models the slip surface through the wall facing. The slip surface slices the affected grid layers and shears or bulges the SRW facing units. The designers performing ICS calculations can now model the entire wall design envelope in one comprehensive calculation. These calculations include the effects of the infill and retained soil strength, the individual grid layer strengths and spacing and the shear and connection strength the SRW facing brings to the system.
The distinctions between an ICS analysis and a global stability analysis form a clear line of design responsibility. A site civil or wall designer should review the ICS
above the base material and through the wall facing within the design envelop for each wall designed on a site. For the larger
site stability design, the owner through their geotechnical engineer should be responsible for the global stability of the entire site including
the soils below the base material of all walls and structures designed on the project site.
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