Settlement Analysis for Construction of a Road Embankment Over Soft Soil Deposits: A Case Study from Taree, NSW, Australia

This paper presents the procedure adopted for the three-dimensional numerical simulation of a road embankment constructed over deep alluvial deposits at a site in Taree, NSW, Australia. The road embankment forms part of mixed-use development along the banks of the Manning River and extends for a length of about 450 m, has a maximum height of 4.9 m and crosses a small creek. The creek runs below the eastern end of the embankment via a concrete culvert with wingwalls. A series of geotechnical investigations along the proposed alignment of the embankment have been completed and identified soft compressible soils. This information was used to develop a 3D subsurface model. The Three-Dimensional Finite Element (3D FE) consolidation analysis was carried out using PLAXIS 3D program. Staged modelling was completed to simulate the construction of the embankment, preloading and the long-term traffic surcharge loading. The analysis was carried out to provide guidance on both the magnitude and period over which settlements will occur. This allowed advice to be provided on the preload period required to limit the magnitude of settlements to those that could be tolerated by the concrete culvert, wingwalls, retaining walls, services and road pavement. Monitoring of the embankment during construction and preloading was completed over an eight-month period. The monitoring results were then used to calibrate and refine the predicted embankment settlement and potential impact on the concrete culvert, wingwalls, retaining walls, services and road pavement over their design life.