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Q: As of 2020, there are new, updated designs for mechanically stabilized earth walls in AASHTO. In short, there are new methods to calculate the maximum force (Tmax) that incorporates design methods for extensible reinforcements (i.e., geosynthetics). They include limit equilibrium and stiffness methods. I was wondering if you can mix and match concepts from the two methods to form a hybrid way of calculating Tmax?
A: There was a robust short course at Geosynthetics 2023 in Kansas City, Mo., that addressed this question. Dr. Dov Leshchinsky (University of Delaware), ADAMA Engineering Inc., and Daniel Alzamora (U.S. Federal Highway Administration) put on a fantastic short course that provided an overview of the American Association of State Highway and Transportation Officials (AASHTO) 2020 methods for the design of geosynthetic reinforced walls. They discussed the stiffness method and the limit equilibrium method at length. While discussing internal stability, geometry, surcharge loads, external stability and seismic design, they clearly stated that you cannot mix concepts from the two design methods. The Transportation Research Board’s (TRB) presentation “Updating Designs for Mechanically Stabilized Earth Walls in AASHTO,” October 8, 2020, is outstanding and available at the following: