USE OF FULLY SOFTENED VERSUS PEAK STRENGTH TO PREDICT THE CAPACITY OF FOOTINGS ON GEOSYNTHETIC REINFORCED SOIL

Abstract

A database of load tests performed on geosynthetic reinforced soil (GRS - reinforcement in this study is of the extensible variety) was developed using results of recent load tests performed on large scale GRS structures at the Federal Highway Administration's Turner Fairbank Highway Research Center as well as results from the literature. The measured capacities were compared to those predicted using the Wu and Pham (1) equation utilizing both the peak and fully softened soil shear strength parameters. It was found that the fully softened strengths yielded capacities that agreed better with the measured capacities. A rationale for this finding is that the robust reinforcement in a GRS strengthens the soil considerably causing the GRS to experience large strains prior to failure. Because the soil peak strengths are mobilized at relatively small displacements/strains even in large scale direct shear or triaxial tests compared to the GRS load tests, it is postulated that the fully softened values are more appropriate to estimate the GRS bearing capacity. A follow-on to this is that since large movements are required to fail say a GRS abutment, the design of GRS abutments will most likely be governed by the serviceability limit state rather than the ultimate limit state.