ON THE CALIBRATION OF UBCSAND CONSTITUTIVE MODEL AGAINST MONOTONIC & CYCLIC TRIAXIAL COMPRESSION DATA FOR BALLAST AGGREGATES

Understanding the mechanical behavior of ballast aggregates under multi-axial loading is key in railway foundation analysis and design. UBCSAND is an effective-stress constitutive model which can predict static and dynamic behavior of granular materials under combined shear and normal stresses. This study presents results from a suite of triaxial monotonic and cyclic compression tests for four different aggregates (gabbro, limestone, demolished concrete, steel slag) and discusses the applicability of UBCSAND model for simulating the relevant non-linear stress-strain curves. To this end, UBCSAND is integrated, for the first time, analytically for shear and volumetric strains, to facilitate calibration against experimental data. Four novel solutions are derived, expressed in terms of monomials and Gauss' hypergeometric functions (2F1) of the stress ratio (q/p'). Variation in the calibrated parameters is discussed considering different loading conditions and types of aggregates.