The construction of a 1 400-mm-wide concrete high-density polyethylene- (HDPE-) lined sewer of 1 850 m in length, expected to be completed in November, forms part of Phase 1 of the four-phase Driftsands sewer augmentation project, which started in the second quarter of 2017 to increase the capacity of the existing Driftsands collector sewer in the Walmer area of Port Elizabeth.
The value of the Phase 1 project is R52.8-million and also consists of 26 manhole structures, one diversion chamber and bulk earthworks.
Precast concrete products manufacturer Rocla was contracted to supply Class 75D HDPE lined pipes and manhole access pipes.
“We started manufacturing the 780 lengths of 1 400-mm-diameter Class 75D HDPE-lined pipes in May 2017, at an average rate of eight pipes per day. We achieved this by double stripping our four available moulds, and we delivered the first pipes to site in July 2017,” says Rocla Port Elizabeth sales consultant Graham Howell.
Rocla made further design changes during the manufacturing of the manhole rings and offered rings and cover slabs with internal HDPE liners and believes this could become the accepted and required standard for all future outfall sewer projects.
“We made minor improvements to the product after a number of on-site visits and we continued with production for the remainder of the year. Ten manhole access pipes were also ordered and these were cut in the Rocla yard to specification, which allowed the laying of pipes to continue uninterrupted, thus giving the contractor the opportunity to achieve good production on site,” Howell explains.
He indicates that Phase 2 will present Rocla with new and interesting challenges as the conditions include rock and deep trenches, but the company is confident in its ability to overcome the challenges, as well as in its manufacturing capabilities.
Howell notes that the existing sewer – which was constructed in 1983, and is a gravity sewer – cannot be upgraded from a technical perspective, however, the realignment of the line route is currently being undertaken.
“The first 1 460 m is parallel to the existing 1 050 m Driftsands collector sewer and then branches off to by-pass the planned extension of the Port Elizabeth Airport runway,” he explains.
He says the increase in residential and commercial developments in Walmer, in addition to the estimated increasing needs requirement by 2020, was a crucial factor for the Nelson Mandela Bay municipality to increase the capacity of its existing Driftsands collector sewer.
Howell believes that on completion, the 4.2 km four-phase project will have addressed the sewerage requirements for existing and future developments for the western suburbs of the Nelson Mandela Bay municipality.