TRENCHLESS TECHNOLOGY
REHABILITATION UNDER WAY ON CAPE FLATS 1 SEWER LINE Demonstration prior to commencement of works on Cape Flats 1
The Cape Flats 1 and 2 (CF 1 and 2) sewer lines were originally installed in 1962 and 1969 respectively. Now a major refurbishment programme is under way in stages. Alastair Currie speaks to Vuyo James, Pr Tech Eng, Senior Professional Officer: Planning, Design and Projects at the City of Cape Town, about the trenchless technique employed. Based on recent pipe profiling inspections, what is the current overall condition of the CF 1 and 2 lines? VJ For background information, Athlone is the starting point for CF 1 and 2 – each measuring approximately 14 km in length – culminating at the Cape Flats Wastewater Treatment Works in Zeekoevlei. A further line, Cape Flats 3 (CF 3), was completed in 2016 to meet ongoing population growth and industrial expansion. Given their age, CF 1 and 2 have stood up remarkably well over the years, but it’s time for an intensive maintenance intervention to further extend their working life. Thanks to the addition of CF 3, we can embark on a systematic and phased refurbishment of CF 1 and 2 without comprising on sanitation delivery. The refurbishment programme starts with CF 1, where pipe diameters range from 1 050 mm to 1 430 mm.
Based on the contractor’s profiling of the pipelines, it was shown that the pipelines have a severely corroded soffit. From these profiling inspections, it was determined that the pipeline ovality varies from between 2.5% to approximately 14%. It was determined, however, that the pipelines are only partially deteriorated, as the severely corroded sections of pipe were encased in concrete at the time of construction. The corrosion of the pipelines has an impact on their flow condition and the high potential of collapse, plus the requirement for point repairs in the future. Which trenchless technology repair interventions have been approved by the City and why? Spirally wound pipe (SWP) lining is the preferred technology to be used for the rehabilitation of CF 1. This is based on the fact that the SWP liner caters for a wide range of deterioration conditions with a single lining profile thickness. This allows for a lower risk to the City and contractor in ordering material in advance, as this material satisfies the design requirements for multiple conditions with a high safety factor.
Vuyo James, Senior Professional Officer: Planning, Design and Projects, Water and Sanitation Directorate, City of Cape Town
22
IMIESA June 2022
The option of SWP fixed-diameter technology is being used, as this provides the City with the best solution in terms of the use of cleaning equipment and the lifespan of the rehabilitated pipeline. The major benefit of SWP is that it can be installed under live conditions. Where practical, it will be used for the whole of CF 1. What are the project costs, phases and timelines? The overall CF 1 project has been split into multiple works packages spanning a tender term of three years. Due to the unknown conditions of the pipeline at the commencement of the project, the CF 1 rehabilitation works have been split into two main phases, namely: cleaning, inspection and profiling; and SWP rehabilitation. Our first section on CF 1 needed to be completed ahead of a City Integrated Rapid Transit project commencing in Govan Mbeki Road on 1 July 2022. The length of this 1 100 mm diameter CF 1 section is approximately 1.2 km starting at Pinati Estate in Athlone and extending to Govan Mbeki Road in Wetton. The works began in mid-April 2022 for scheduled completion by the end of June 2022. The approximate cost is R27 000 per metre inclusive of cleaning, all civil works and rehabilitation.
