Refinement of K-stiffness Method for geosynthetic-reinforced soil walls

The K-stiffness Method is an empirically-developed working stress method used to compute reinforcement loads for the internal stability design of geosynthetic-reinforced soil walls under serviceability conditions. In this paper, additional data from Japanese case studies for five full-scale field and three full-scale laboratory geosynthetic-reinforced soil walls are added to the database that was used to calibrate the original K-stiffness Method. One more case study from an instrumented wall in the USA is also introduced. Measured loads are compared with predicted loads using the current AASHTO Simplified Method and a modified version of the K-stiffness Method that has been adjusted by back-fitting model parameters to the extended database. The AASHTO Simplified Method is shown to be excessively conservative (on average) with respect to accurate prediction of reinforcement loads and to correlate poorly with measured values. The modified K-stiffness Method is demonstrated by statistical analysis to give ratios (bias) of average measured to predicted reinforcement load values close to 1 and coefficient of variation (COV) values for the maximum reinforcement load in a wall that are less than 25%.