Abstract:
The Melbourne Arts Centre redevelopment involved excavation of a 10 to 15 m deep basement within Coode Island Silt, a very soft, normally consolidated clay, with a high groundwater table. Due to legacy ground anchors from the original Arts Centre structure posing physical constraints on the type of retention system, it was determined that secant piles and diaphragm walls were not practical. The final retention solution adopted, comprised soldier piles with jet grout in-fill columns and a jet grout base block, restrained by CFA and polymer-supported bored tension piles extending to depths of up to 32 m to resist uplift forces.
Managing groundwater inflow and wall performance during excavation in soft soils was a key geotechnical challenge. Jet grout columns were used primarily to limit seepage and support local soil retention between the soldier piles. The jet grout base block provided additional resistance to base heave and contributed to the effectiveness and stability of the overall retention system in combination with the tension piles. Due to the presence of the existing anchors, careful coordination and modification of both tension, retention pile locations, and the grout block geometry was required.
Access limitations beneath the heritage-listed spire added further complexity, necessitating low headroom polymer-supported bored piling in restricted zones. Elsewhere, CFA tension piles were adopted, all of which required full-length reinforcement cages to meet uplift and shear design requirements.
This paper presents the geotechnical design approach, construction methodology, and key lessons learned in delivering a combined foundation and retention system within soft ground under tight urban and heritage constraints. It provides insight into the application of jet grouting as a seepage control technique alongside deep foundation systems in challenging excavation environments.