Woolgoolga to Ballina Pacific Highway Upgrade – Embankment Performance Monitoring and Back-Analysis

The section of the Pacific Highway Upgrade project between Woolgoolga and Ballina (W2B) traverses areas having significant depths of soft soils. The presence of these soft soils causes significant risks in relation to timely project completion and potential cost blow out. To reduce these risks, soft ground treatment using wick drains and preloading was used in the form of Early Works to de-risk the project and to reduce the post construction settlement. During the embankment construction and preloading period, instruments were installed to monitor the embankment performance. Monitoring was carried out using an innovative web-based system to enable continuous and real time monitoring of embankment performance, technical review and modifications of construction sequence as required.

Monitoring data were back analysed periodically to assess the embankment performance. Through this exercise, additional filling and stability measures were implemented over a number of embankment sections, where the monitored embankment settlements exceeded the design prediction. In addition to the innovative web-based monitoring system, advanced numerical modelling was used to predict future creep settlement using the back-analysed results. It was found that advanced numerical modelling of creep settlement must carefully consider the two-dimensional stress distribution beneath the embankment including toe berms in order to model accurately the stress history and over-consolidation effects on creep after surcharge removal. When the two-dimensional stress distribution is properly taken into account, the results of forward creep prediction matches well with one-dimensional analytical methods such as that proposed by Wong (2010).