Ground Engineering
Marine Parade — CFA Piling & Retaining Wall
Three rows of 600 mm CFA piles and a GCS retaining wall — road edge ground improvement at Mellons Bay, Auckland.
- Location
- Marine Parade, Mellons Bay, Auckland
- Client
- Fulton Hogan
- Designer
- Andy O'Sullivan Geotechnical Engineering
- Timeline
- December 2022 — January 2023
- Scope
- CFA piling, GCS retaining wall, USCS testing
Design
Stabilising the Road Edge at Mellons Bay
Marine Parade at Mellons Bay, East Auckland, required ground improvement works to address a deteriorating retaining situation threatening the carriageway. GSI was engaged by Fulton Hogan as a specialist subcontractor, with design by Andy O'Sullivan Geotechnical Engineering.
The design involved undercutting the low-strength slip debris and constructing two counterfort drains and a subsoil drain along the base of the cut batter. Three rows of 600 mm diameter CFA piles were specified to a depth with 1.0 m embedment into the underlying weathered rock, followed by construction of a Geosynthetic Cellular Structure (GCS) retaining wall to 500 mm below road level. The CFA piling approach offered a non-disruptive installation method with minimal vibration impact on adjacent properties.
Build
CFA Piling and GCS Wall in Constrained Conditions
Works commenced with road edge excavation and access ramp construction to establish a working platform. A layer of A29 bidim cloth was placed across the undercut subgrade and backfilled with AP65 hardfill to an average 500 mm thickness. CFA columns were then constructed using GSI's FD45 CFA piling rig, spaced at 1.8 m centres and installed between 6.2 m and 11 m depth depending on the depth to weathered rock. Embedment of 1.0 m into weathered rock was verified by monitoring drilling torque pressure and visually assessing drilling spoil.
The GCS retaining wall was constructed with Cirtex Duramesh facing panels, with AP65 placed in 200 mm compacted layers and Stratagrid SGU80 geogrid repeated at each lift. USCS testing was carried out on site materials throughout to verify fill quality and compaction acceptance criteria.
Deliver
Road Edge Secured, January 2023
The Marine Parade project was completed in January 2023, delivering a permanent, engineered solution to the road edge instability. The combination of CFA piles and the GCS retaining wall provides long-term structural support with a finished appearance suited to the coastal residential context.
GSI provides specialist CFA piling, ground improvement, and retaining wall construction across Auckland and New Zealand-wide — delivering technically detailed solutions to constrained suburban and coastal sites under single design-build contracts.
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