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Zandvliet Wastewater Treatment Works Upgrade
This premier water infrastructure project located in Khayelitsha in the Western Cape, was undertaken for the City of Cape Town by the Stefanutti Stocks Coastal region. The duration of the contract runs between November 2018 and November 2022.
Background: The existing 72 Ml/d Zandvliet Wastewater Treatment Works (WWTW) was overloaded, as well as suffering from failing plant infrastructure (equipment and pipelines). Urgent rehabilitation was required to meet the rising needs of the region, and upon completion of the upgrade the plant would process up to an additional 18 Ml/d, bringing its capacity to 90 Ml/d.
The Project Scope
Stefanutti Stocks Coastal’s Cape Town-based civils team undertook the expansion of the Zandvliet Wastewater Treatment Works which included the construction of new enlarged inlet works, two new screw-pump stations, four new primary settling tanks, a primary sludge pump station, a sludge dewatering building, a service water pump station, a Waste Activated Sludge (WAS) pump station, sundry holding tanks (two primary sludge and two WAS), pipelines, access roads, as well as some minor services (water connection, site drainage etc). Following the completion of the live diversion to the new works a portion of the old inlet works structure was demolished.
Technologies and Challenges
- The project featured an extremely complicated inlet works (situated ten metres below ground level and approximately seven metres below the water table) that required staged dewatering as well as construction of a raft foundation, comprising 700m3 of continuous concrete, to anchor the table pump station located below the water table.
- Approximately 6 000m2 of Anchor Knob Sheet (AKS) lining was applied to the walls of the enclosed structures and pipelines – these liners protect against chemical attack in aggressive environments and are designed to extend the life of concrete structures. Their installation is challenging as AKS is applied as a ‘cast-in’ sheet that is cast monolithically with the concrete wall pours.
- The installation of new pipelines – including 1.8m diameter concrete pipes in-between existing services and within a working plant – required precision, care, risk identification and management thereof.
- The high-level technical aspects of the project and the sheer number of stakeholders involved, presented the perfect opportunity for the visualization of the designs.
- The plant is gravity-fed with no retention capacity, thus connecting the new works was a live tie-in operation. This required meticulous planning and execution.
The City of Cape Town’s corporate services directorate entered the project for an international project management related award.
- Concrete: 13 500m3
- Reinforcing: 1 440 ton
- Formwork: 35 783m2
- Excavation: 259 880m3
- Backfill: 180 000m3
- Pipelaying: 4973m
Stefanutti Stocks Coastal: Civils Discipline
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