Long-term performance of soft ground improvement at an approach embankment of a bridge

The soft ground improvement of an approach embankment for abutments of a major bridge was designed as part of a highway upgrade project in northern New South Wales, Australia. The adopted soft ground treatment approach was to preload and surcharge the ground using prefabricated vertical drains to accelerate the consolidation process. Hold Point for surcharge removal at the southern abutment was released after the review and back-analysis of available monitoring data (mainly settlement plates, piezometers, extensometer, and hydrostatic profile gauge). The surcharge was removed in March 2018, and the bridge approach was completed in June 2019. In mid-October 2019, settlement of the approach slab was noted with some major cracking of the F-type barrier CPTu tastings were carried out in November 2019 to assess the soft ground condition after the surcharge. Subsequently, reassessment of the performance of the main embankment and approach embankment were carried out. The back-analysis results were used to predict the future performance of the approach embankment and its impact on piled foundation. A few lessons learned with regard to the design approach, back-analysis, and construction staging are presented.