Construction World January 2018

THIS PROJECT WAS ENTERED IN BEST PROJECTS 2017

PROJECT PROFILE

MICRO-TUNNELLING for Cape Flats 3 BULK SEWER

Construction of the Cape Flats 3 Bulk Sewer – Phase 2 (CF3-2) was, at the time of writing, on track to reach practical completion in October 2017, within budget and on programme, despite many complex technical challenges.

Scope of work The design of the CF3-2 was undertaken by AECOM between 2012 and 2015, which included comprehensive assessments of various alignment options, as well as an evaluation of long-term operational requirements, considering the strategic nature of the sewer. The CF3-2 starts at the Bridgetown Pump Station as a rising main and ultimately discharges into the existing section of the Cape Flats 3 Bulk Sewer (CF3-1) which was constructed in 1996 and currently links the Philippi Interceptor Sewer to the Cape Flats WWTW. Engineering and public liaison Determining a route for the construction of a large-diameter pipeline through a densely built-up area was extremely challenging. The CCT’s initial preferred route had to be modified significantly after investigations revealed a clash with existing and future planned high-voltage electrical cables. The vertical alignment of the CF3-2 was largely determined by the natural topography and the significant number of existing service crossings along the final horizontal alignment. These constraints required that the rising main pipeline extend for over 5 km before discharging into a short section of gravity sewer which ties into the CF3-1. Flow Assessment Ultimately, the optimum design capacity of the CF3-2 was determined to be 1 300 ℓ/s.

T his project stands out because of its innovative design aspects, such as the inclusion of a barometric loop with vortex drop structure, and state-of-the-art construction methods, including steel sheet pile shoring and micro-tunnelling. The successful completion of this project was also made possible with effective co-operation among the project team, comprising the City of Cape Town (CCT) as a very much hands-on client, involved in all decision-making processes; AECOM as the consultant, ensuring strict adherence to the specifications; and CSV Construction as the main contractor, upholding a high level of

area of the Cape Flats, as well as providing a link for transfer of flow between two bulk wastewater catchment areas. However, these are currently severely dilapidated and silted up, and therefore cannot perform their strategic function adequately. Completion of the CF3-2 is the final link in the system, greatly increasing the system capacity to allow rehabilitation work to be undertaken on the old sewers, as well as providing sufficient capacity in the system for at least the next 50 years. The CF3-2 will provide a vital link for the conveyance of wastewater from a large portion of the Cape Flats area to the Cape Flats Wastewater Treatment Works (WWTW), adjacent to the False Bay coastline. In addition, the CF3-2 will have the capability of diverting a portion of the wastewater discharging currently at the Athlone WWTW to the Cape Flats WWTW.

innovation and workmanship. Purpose of the project

The City of Cape Town’s existing twin Cape Flats Bulk Sewers (CF1 and CF2), constructed in the 1960s, serve an 8 000 ha

Construction of isolating/scour combination valve chamber. (Photo: Terry February)

Project information • Client: City of Cape Town • Contract value: R252 354 • Start date: July 2015 • End date: 25 October 2017

• Main contractor: CSV Construction • Project manager: City of Cape Town • Consulting engineer: AECOM

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CONSTRUCTION WORLD JANUARY 2018