A Practical Framework for Parameter Selection and Calibration of the Barcelona Basic Model for the Mechanical Behaviour of Unsaturated Collapsible Soils

The Barcelona Basic Model (BBM) is a well-established constitutive framework for describing the mechanical behaviour of unsaturated collapsible soils within the context of critical state soil mechanics. Despite its robustness, its application in engineering practice remains limited due to the complexity of its formulation and challenges associated with reliable parameter determination. This study presents a practical framework for the selection and calibration of BBM parameters for Jossigny silt, using laboratory test data reported in the literature, employing a sequential approach supported by engineering judgement and a clear understanding of the original model formulation. The calibrated parameters are implemented in PLAXIS to simulate laboratory tests with different stress paths, allowing for the evaluation of the model’s ability to reproduce observed soil behaviour compared with those reported in the literature through a benchmark exercise conducted using the same reference tests. The calibrated parameter set successfully reproduces soil response under different stress paths, capturing the mechanical behaviour by achieving average values of R2 = 0.98, MAE = 0.01, and RMSE = 0.013. The proposed framework is intended to bridge the gap between advanced constitutive modelling and routine engineering analysis by providing a transparent, step-by-step calibration procedure readily implementable in commercial finite element software.