Calibration of an advanced constitutive model through direct shear test results

In many geotechnical problems, failure conditions involve the formation of a narrow shear band where shear strains localize. In this study, the thickness of the shear bands was indirectly determined based on the results of constant normal load direct shear (CNL) tests carried out on sand specimens reconstituted at three different relative densities. The adopted procedure also allows to evaluate the soil deformations within the shear band and, thus, to correctly locate the critical state line in the compressibility plane. The results of the CNL tests were used to calibrate the Severn-Trent model, an advanced constitutive model proposed by Gajo and Wood, apt to well-reproduce the mechanical behaviuor of sands from small to large strain levels. The predictive capabilities of the model were confirmed by the good agreement with the experimental data obtained performing constant normal stiffness direct shear (CNS) tests. Finally, the shaft bearing capacity of a bored pile embedded in a homogeneous soil layer was numerically evaluated and compared to the one predicted using a less sophisticated (classical) approach.