Numerical modeling of triaxial tests on clays with sand-column inclusions -

Abstract

Ground improvement of soft soils using granular inclusions is an efficient technique that increases the rate of consolidation, reduces settlements, and enhances the load-carrying capacity of the composite system. The finite element method (FEM) has been widely implemented to study different aspects related to the behavior of the composite system such as the effect of column installation, column encasement, and the column group behavior. Triaxial testing has been widely adopted in the experimental studies because it allows controlling the confining pressure, loading rates, and drainage conditions of the sample. The use of FEM to model triaxial tests is restricted to samples with a homogeneous soil material and focuses mainly on the effect of boundary conditions and the applicability of different constitutive models to capture soil behavior. Also, the FEM studies were limited to fully drained or undrained conditions, whereas the response of soft clays that are reinforced with granular columns is expected to be affected by the rate of loading and drainage conditions, and the field behavior of the composite system is expected to be partially drained. The objectives of this study are to (1) characterize thoroughly the proper modeling conditions that facilitate simulating conventional consolidated drained (CD), undrained (CU) and consolidated partially drained (CpD) triaxial compression tests involving non-homogeneous specimens composed of clay and granular inclusions, (2) verify the models results using selective high quality experimental triaxial tests that are published in the literature, (3) investigate, numerically, the mechanism of partial drainage between sand and clay during triaxial testing, and (4) complement the analysis with a field-scale application that will be simulated using the proposed finite element model. The significance of partial drainage in the field is highlighted in this application, and its impact is investigated on the design parameters involved in systems of clays reinforced with sand colu