Peak versus residual shear strength in geosynthetic-reinforced soil design

Current design guidelines for geosynthetic-reinforced soil structures disagree over the shear strength parameters that should be selected to characterize the backfill material. Most geosynthetic reinforcing materials are classified as extensible inclusions for almost all practical applications. The extensible nature of geosynthetic reinforcements has led to the recommendation by several agencies and reinforced soil designers toward the use of the residual shear strength instead of the peak shear strength for design. However, common practice in the US has been the use of the peak shear strength. The main purpose of this paper is to provide experimental evidence regarding selection of either peak or residual shear strength to characterize the backfill material for the design of geosynthetic-reinforced soil structures. Specifically, experimental results from reduced-scale models tested in a geotechnical centrifuge indicate that the stability of geosynthetic-reinforced slopes is governed by the peak soil shear strength.