Evaluation of K-stiffness method for vertical geosynthetic reinforced granular soil walls in Japan

in this paper the K-stiffness Method as originally proposed by Allen et al. (2003) is re-examined using a total of six new case studies-five from Japan and one from the USA. A common feature of the walls in this new data set is that the walls were all constructed with a vertical face and a granular backfill. However, the walls varied widely with respect to facing type. This new data set together with data for vertical walls previously published by Allen and Bathurst (2002a,b) and Allen et al. (2002) is now used to isolate the effect of the facing stiffness factor on reinforcement loads and to adjust the original equation that was developed to calculate its value. The paper also shows that predicted reinforcement loads using the current AASHTO Simplified Method in the USA and the current PWRC method in Japan give the same reinforcement load predictions, and both grossly over-estimate the values deduced from measured strains. The new data set is used to slightly refine the estimate of the facing stiffness factor used in the original K-stiffness Method. The original and modified K-stiffness Method are demonstrated to quantitatively improve the estimate of the magnitude and distribution of reinforcement loads for internal stability design of vertical-faced geosynthetic reinforced soils walls with granular backfills when compared to the current American and Japanese methods.