Application of the Simplified Stiffness Method to Design of Reinforced Soil Walls

In an earlier paper, the writers proposed modifications to the AASHTO simplified method to address shortcomings in the method and to improve reinforcement load predictions for walls under operational conditions. The new method is called the simplified stiffness method to emphasize the importance of reinforcement stiffness on reinforcement loads rather than strength as in the current AASHTO approach. The method provides a seamless transition for walls built with soil reinforcing elements ranging from inextensible steel to relatively extensible geosynthetics. The accuracy of the new approach is examined statistically and predicted loads are demonstrated to be more accurate than loads computed using the AASHTO simplified method and a log spiral limit equilibrium-based approach. The paper shows how the simplified stiffness method can be applied within a load and resistance factor design (LRFD) framework. To ensure that the reinforced soil zone remains within working stress conditions, a new limit state to address failure of the soil within the reinforced soil zone is introduced and applied within the LRFD framework. Step-by-step design examples for three different wall cases constructed with cohesionless backfill soils are provided in the Supplemental Data for the paper.