Observations on the mobilization of strength in reinforced soil structures

Confidence in the design of reinforced retaining structures is based on a limited body of experimental field data from performance monitoring of a relatively small number of case studies. In order to improve upon that confidence in design, this research addresses the back-analysis of the only field study involving a reinforced steep slope with independent measurements of tensile force and strain, which was first described by Fannin & Hermann (1990). Knowing the mobilized strength in the reinforcement, a back-analysis was performed using widely accepted design practice, with the purpose of establishing the mobilized angle of friction within the backfill soil of the structure. The mobilized friction angle was compared with the findings of laboratory shear strength tests in direct shear, triaxial and plane-strain conditions. The comparison provides further evidence in support of the expectation that plane-strain conditions prevail within the reinforced steep slope, and the recommendation in the British code of practice to use the peak friction angle for design. Additionally, visual inspection and index testing on exhumed geogrid samples from the structure described by Fannin & Hermann (1990) established that the geogrid has experienced no major physical damage, nor any significant degradation associated with durability of the polymer material. Moreover, rapid loading creep tests data show excellent agreement between exhumed and typical values, implying no significant durability degradation in the geogrid of the Skedsmo structure. Accordingly, isochronous load-strain-time data can be used with confidence for predicting the long-term strain of geogrid reinforced soil structures.Applied Science, Faculty ofCivil Engineering, Department ofGraduat