Construction World December 2017



densely-populated area of Cape Town, where significant sections of the pipeline would need to be installed beneath narrow and busy roadways. Microtunnelling is a specialised pipe-jacking operation, preceded immediately by a Tunnel Boring Machine (TBM) that removes soil mechanically from the jacking face using a slurry process. The TBM is operated remotely from a control centre on the ground surface. No human-entry into the tunnel is required. Due to the nature of this project, there were many safety risks that had to be managed daily on-site. • Company entering : CSV Construction • Client: City of Cape Town • Contract value: R252 354 447 • Start date: July 2015 • End date: 25 October 2017 • Main contractor: CSV Construction • Project manager: City of Cape Town • Consulting engineer: AECOM

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

This 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 microtunnelling. 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. The design of the CF3-2 was undertaken by AECOM between 2012 and 2015. All works have been constructed to a high quality, based on a strictly enforced specification. The contract included 5 050 m of 1 000 mm diameter ductile iron rising main, and 250 m of 1 200 mm diameter concrete gravity sewer. In addition to the new bulk

sewer, the contract included five air-valve chambers, four isolating/scour combination valve chambers, one discharge chamber, and two manholes. All chambers were constructed in situ, and made to withstand groundwater pressures without seepage. Due to the limited workspace available along much of the route, and depths ranging between 2,5 m and 4,5 m, in sandy ground conditions with a high water table, the design and contract specifications took into account that a large portion of the pipe-trench excavation would need to be undertaken using a suitable shoring system. CSV Construction’s preferred method was to use interlocking steel sheet piles, since the system also acts as a coffer dam, thereby limiting the dewatering requirements during construction. The 5,3 km CF3-2 route traverses a

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