Finite element analysis of embankment on soft Indian River clay

Abstract

This thesis re-analyzed the performance of an approach embankment for a new bridge across the Indian River Inlet in Delaware. The 115 ft. wide mechanically stabilized earth embankment (up to 45 feet above ground level) was founded on a 60 ft. deep layer of soft clay. Consolidation of the soft, normally consolidated clay was accelerated through installation of an array of prefabricated vertical drains. The performance was monitored during staged construction and for a period of 1.25 years after construction (2006-2008). During this, the embankment settled up to 6.5 feet, while large lateral spreading in the clay was restrained by overlying sand layers. The side walls tilted by up to 1.1°. The measured ground movement far exceeded the expectations of the designers and the embankment was eventually dismantled in 2008. The current research evaluates site conditions from field investigations carried out in 2003 and 2007 which included a program of 1 -D consolidation and triaxial laboratory shear testing on clay samples. Plane strain numerical analyses were carried out using PLAXIS 2D AETM using the Modified Cam-Clay and MIT-E3 effective stress models to represent clay behaviour. The numerical predictions are generally in very consistent agreement with measured settlements below the embankment and with lateral deflections measured by inclinometers. The analyses show significant lateral deformations arise due to asymmetry in the loading particularly during the staged construction of the embankment. The current results suggest that the measured performance could be credibly predicted using available site investigation and laboratory test data.