The case for true probabilistic internal stability design of geosynthetic MSE walls

ABSTRACT: The paper makes the argument for a fully probabilistic approach to quantify the margins of safety for the internal stability limit states for geosynthetic mechanically stabilized earth (MSE) walls. The three limit states considered are tensile strength, pullout and the soil failure limit state that appears in the stiffness method. The methodology is based on statistical quantification of the accuracy (bias) of load and resistance terms that have been collected from large databases of instrumented MSE walls for load side models, and laboratory measurements compiled in databases for resistance side models. A closed-form solution is presented to compute the reliability index for internal stability limit states with lognormal distributions of bias values and nominal values. The concept of level of understanding that appears in Canadian load and resistance factor design (LRFD) practice appears in the formulation and thus allows for the injection of experience into the probabilistic approach. The general approach provides a quantitative link between the classical factor of safety used in working stress design past practice, and margins of safety expressed within a probabilistic framework. The closed-form solution is used to compute the reliability index for the three limit states for as-built polyester (PET) strap MSE walls.