Implementation and Use of the Bounding Surface Plasticity Geomaterial NTUASand02

The numerical description of the undrained cyclic behaviour of sandy soils still represents a challenging issue in evaluating the response of geotechnical systems in seismic conditions. To this end, a large number of constitutive models have been developed over the years, with positive implications and limitations in capturing the soil response. In particular, the bounding surface plasticity theory has proven to be a valuable framework for reproducing the hardening soil response under both drained and undrained conditions. To increase the computational capabilities of the analysis framework OpenSees in assessing the dynamic response of soils, in the present study the well-known bounding surface plasticity model developed by Papadimitriou and Bouckovalas (2002) [1], referred to as NTUASand02, has been implemented as a new NDMaterial in OpenSees. The new source code can be used under both plane-strain and three-dimensional conditions. It provides an advanced analytical formulation that implies a delicate evaluation of a set of input parameters controlling the hardening features and pore water pressure build-up. Hence, a sensitivity analysis at the scale of the volume element is here proposed to point out clearly the influence of the constitutive parameters on the response. First, the effectiveness of an existing calibration procedure of the input parameters is shown with reference to a well-characterized sand. Then, monotonic and cyclic triaxial tests are simulated to address the influence of a variation in the model parameters requiring a trial-and-error calibration.