Paarl waste water upgrading kicks off
2009-07-30
THE project to upgrade and prolong the life of the waste water works of Paarl was recently launched, and includes the laying of a huge sewage pipe through Paarl to Boschenmeer (about 10 km). The project has been necessitated by the expansion of Paarl in a southerly direction. A specialist in precast concrete infrastructural products, Rocla, was awarded the contract to supply the precast concrete pipe, which will be laid as deep as 6 metres underground. This is part of the process to increase the amount of waste water processed from 24 Ml to 35 Ml per day. Rocla is required to include bends in the pipeline to meet the need for the free flow of the waste water. Phase 1 of the pipeline comprises concrete pipes between 1050 and 1650 mm wide with an internal sacrificial layer made from Calcium Aluminate Cement (CAC) to deal with the corrosive nature of the contents. Another specialised product that Rocla uses in Phase 2 of the project was the HDPE (High Density Polyethylene) liner, manufactured by Engineered Linings. The HDPE liners can withstand aggressive water conditions inside the pipes, which assist in prolonging the lifespan of the sewer system. Rocla used a 3mm thick lining with 10mm knobs, which can sustain approximately 40kg of reverse pull forces. They custom-made a 45 degree pipe using a top cast mould, where each bend is divided into two components, each with a 22,5 degree bend, instead of the normal lobster back bend with corners and edges. According to Hendrik Stander, Rocla’s Sales Executive at the Blackheath plant, manufacturing the bend in two parts means that the handling of the bend is easier and quicker. Each bend weighs 6,3 tons per 22,5 degree bend. “One of the trickier parts of this particular project,” adds Stander “was laying the bended pipes in the correct position of up to six metres deep. “Access holes were precast into the bends to ensure easy access during inspection. Manhole rings will be placed on top of these access holes.” To further facilitate the free flow system, Rocla designed a 90 degree bend which is divided into three 30 degree bends. “The thrust block on the bend played a dual role in supporting the seam and the bend in the ground,” says Stander. Kempen van Wyk, Director of Exeo Khokela Construction, the project’s main contractor says, “Rocla has delivered timeously on all deadlines so far and the project has run smoothly from the start. “Our close working relationship has played an important role in delivering a customised solution for Drakenstein municipality.” Phase 1 (expansion of the waste water works) is already 60% complete and Phase 2 (the sewer pipe) recently commenced. An additional sewage plant is planned south of Paarl (the site has not yet been finalised) and will link up with the sewage system in future (approximately in 2025).
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