Ground improvements and supports for embankments and structures of Regional Rail Link – City to Maribyrnong River

This paper discusses ground improvement and foundation support that were adopted in Melbourne’s Regional Rail Link development that was completed in 2015. The development included realignment of rail track within the existing rail corridor and additional bridges, viaducts, and embankments. The project site was a “brownfield” within a relatively complex geological domain of Yarra Delta Sediments including the recent marine deposits locally called Coode Island Silt (CIS) which is a highly compressible and very low strength clay. The presence of CIS and its variable thickness imposed special challenges for design and construction of the rail link and necessitated ground improvement and support works, including: a) preformed driven, bored and CFA piles for bridges, viaducts and underpasses; b) ground support using controlled modulus columns (CMCs) for the embankments with estimated long term settlement ≥ 150 mm; c) preloading and surcharging for embankments with estimated long term settlement <150 mm. The paper will first cover general geotechnical design considerations for ground improvement using CMCs. A case study will then be presented on the detailed design of the North Melbourne Flyover embankment widening.