On Global Equilibrium in Design of Geosynthetic Reinforced Walls

Common design of MSE walls is based on a lateral earth pressure approach. A key aspect in design is the determination of the reactive force in each reinforcement layer so as to maintain the system in equilibrium. This force leads to the selection of reinforcement with adequate long term strength. It is also used to calculate the pullout resistive length needed to ensure the capacity of each layer to develop strength. Lateral earth pressures used in design may or may not satisfy basic global equilibrium of the reinforced soil mass. Hence, the present work establishes a benchmark test using a simple statically determinate approach, in order to check if different design procedures satisfy equilibrium. Basic statics indicate that such a test is necessary, but not sufficient, to ascertain the validity of the calculated reactive force. Three existing design methods are examined: AASHTO, National Concrete Masonry Association, and Ko -stiffness. AASHTO, which is the simplest to apply and generally considered conservative, satisfies the benchmark test. However, it may yield very conservative results if one considers the facing to play a major role. NCMA is likely satisfactory if one explicitly accounts for the facing shear resistance in assessing the reaction in the reinforcement. The emerging Ko -stiffness approach, which is empirical, may violate statics potentially leading to underestimation of the reinforcement force.