Design, monitoring and back-analysis of highway embankments constructed over soft soil

The Pacific Highway is a highway between Sydney and Brisbane in Australia. It is currently being upgraded to a dual carriageway for its entire 1000 km length. The soft soil embankment design and transition zone design for one of the upgrade sections is presented herein. Due to the limited amount of reliable laboratory data and low embankment heights, the settlement was calculated using the coefficient of volume change, particularly from correlations from CPT results. A short construction programme necessitated the use of a combination of surcharge and wick drains. An in-house spreadsheet calculated the post construction settlement based on the ground conditions in each filled region based on applied ground treatments. Additionally, a unique transition zone solution was used for the bridges in this section of the highway which involved the use of driven piles at increasing spacings away from the bridge abutment. Construction survey data from both embankment settlement and transition zone settlement indicated that the design methods and ground treatments were effective provided a reasonable estimation of the actual ground behaviour.