Laboratory Corroboration of Proposals for Soil Reinforced with Geosynthetic Strips

Industry groups have proposed updating AASHTO's Simplified Method design guidance for reinforced soil to include geosynthetic strips (or straps). If implemented, the use of concrete panel facing for retaining walls would be facilitated, and the corrosion problem of steel would be avoided. This new interest results from observations of retaining walls at St. Remy (France) and Christiana, Delaware (United States). In these retaining walls, k(r)/k(a) of approximately 1 avoids both the settlement associated with smaller values and the capacity reduction of larger values. Parameter k(r) is the horizontal earth pressure coefficient in reinforced soil and k(a) is the active earth pressure coefficient. Previously, FHWA data showed that S/D determines granular stability of geosynthetic-sheet-reinforced soil, where S is vertical spacing between strips and D is diameter of the largest soil particles. Using laboratory tests performed at the University of Colorado Denver, this paper extends the FHWA data from sheets to strips. And, it validates industry observations in terms of the reinforcement coverage ratio R-c equal to b/S-h, where b is the strip's width and S-h is horizontal spacing between strips. For 30 years, engineers have questioned high reinforcement stresses measured in a wall at Guildford Bypass (U.K.), and this paper provides an explanation.