Three pipe-jacking shafts through soft soils, old landfill and steep ground, with thrust blocks designed for jacking loads of up to 600 tonnes.
- Client
- March Cato for Auckland Council
- Services
- Temporary works design
- Location
- Chelsea Estate Heritage Park, Birkenhead, Auckland
- Scale
- 3 shafts · 12 m deep · 600 t thrust
- Status
- Complete 2019
01 / Project overview
The brief
Chelsea Estate Heritage Park is Auckland's largest coastal park and the setting of the historic Chelsea Sugar Refinery, with wetlands, native forest and open grassed promenades. A stormwater renewal through the park involved installing [500 / over 600] m of 2.1 m diameter concrete pipe by pipe jacking.
We designed the temporary works: three large jacking and reception shafts, the thrust blocks that react the jacking load, and the access and working platforms around them. The ground made it demanding. Soft soils and an old landfill sat within the work area, one shaft was on steep ground, and the deepest shaft reached about 12 m below ground level.
02 / Our approach
How we delivered it
Shaft support
The shafts were built using sheet piling and soldier piling, with steel I-section ring beams bracing the walls against collapse. Each design accounted for access, the ground conditions at that location, and surcharge loads from plant and materials at the shaft edge.
Thrust blocks for 600 tonnes
Thrust blocks at the base of the shafts were designed for jacking forces of up to 600 tonnes. At one shaft the soil was too soft to take the full load on its own, so we transferred part of the thrust through the ring beams into the sheet piles, making the shaft structure part of the reaction system.
A platform on steep ground
At one shaft location the slope left no level area for cranes and machinery. We designed a temporary soldier-pile working platform to give the contractor a stable base to work from.
Safe access at 12 m
For the deepest shaft we designed temporary access stairs, and a davit arm mount for moving materials in and out of the shaft. The davit mount was load tested before use.
03 / The outcome
“Each shaft was designed for its own ground and terrain, giving the contractor a safe, workable base to jack 2.1 m pipe beneath one of Auckland’s most valued coastal reserves.”
04 / Gallery
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