Assessment of Model Uncertainty for Settlement-Prediction Models of Spread Footings on Clays Reinforced with Aggregate Piers

Aggregate piers are widely used in ground improvement applications to enhance the stiffness of soft clays and their mechanical properties. The literature includes several studies that are aimed at quantifying the uncertainty in bearing capacity predictions for spread footings that are supported on ground reinforced with aggregate piers. Few researchers, however, targeted the quantification of model uncertainties that are associated with common “settlement-prediction” models for such foundation systems. The objective of this study is to fill this gap by utilizing load-settlement data from full scale load tests for footings on aggregate piers to compare the measured load-settlement response with that predicted using existing analytical methods and numerical tools that are used in practice. The database is also used to quantify the model uncertainty in settlement predictions of available models with particular focus on settlement prediction at the service or design load. The model uncertainty as reflected through the ratio of measured to predicted settlement was found to be relatively high, particularly for the simplistic linear elastic theory-based models (e.g., Priebe). An illustrative reliability-based example is presented to showcase the need for including the effects of model uncertainty in the serviceability-based design of footings on aggregate piers.