Global Level of Safety and Performance of Geosynthetic Walls: An Historical Perspective

A summary of 20 well-documented geosynthetic wall case histories representing a total of 35 analysis conditions is presented. These case histories cover a wide variety of wall heights, surcharge loading, foundation conditions, facing types and batter, reinforcement types and stiffness, and reinforcement spacing. All of the production walls, including some that have been in service for 25 years, have performed well with low reinforcement strains and minimal deflections. Some of the walls were research structures that, although purposely underdesigned, could not be taken to failure, demonstrating that the internal stability design of geosynthetic walls in North America is conservative. Each of the walls was characterized globally with respect to internal level of safety, or resistance to demand ratio. Even when using nonconservative estimates of soil property values and perfect matching of the reinforcement strength to demand, the Simplified Method resulted in approximately 1.5 to 4 times as much geosynthetic reinforcement as that needed to achieve acceptable performance based on actual long-term performance of many of the wall case histories. Based on the analyses presented here, there is a need to re-evaluate the current North American approach to design of geosynthetic walls against internal reinforcement instability.