Thembisile Hani Local Municipality is the first local authority in South Africa to use a new innovative precast-concrete reservoir water-retaining wall system.
It is being used in combination with a tried-and-tested precast-concrete reservoir roof structure technology that has already helped many local authorities in the country accelerate reservoir construction projects.
Monde Consulting Engineers & Project Managers proposed this modular approach of constructing the water-retaining walls to its client to fast-track the delivery of the 10 Ml structure in a very short timeframe.
Sefiso Mdingi, Monde Consulting Engineers & Project Managers’ civil-engineering technologist, says it is based on a system that was designed and developed by Corestruc.
“We were well aware of Corestruc’s work in the field of precast-concrete reservoir roof structures and knew that it had also developed a precast-concrete wall system to further fast-track these projects. We were very impressed with the technology and, therefore, believed that it would be the ideal solution to build the structure in a very short period,” Mdingi says.
Willie de Jager, managing director of Corestruc, says that by constructing the wall in this manner, the critical path of the programme runs through the earthworks and floors.
“The construction of the concrete floor overlaps the installation of the walls and roof on the works programme. We are able to construct the walls and roof in as little as two to three months on site, while the manufacture of the structure takes place at our factory during the earthworks and construction of the foundations,” says Willie de Jager, managing director of Corestruc.
The wall system comprises just more than 60 precast-concrete panels, each weighing eight tons and are 9,8 m in length and 16,4 m in width, as well as four 10,5 t buttress panels.
They were manufactured at the company’s state-of-the-art factory and transported to site where they were installed by Corestruc’s own team.
Mdingi says that it would be impossible to achieve the same level of accuracies on the wall structure using traditional cast-in-place methods, considering the many variables encountered on a traditional construction site.
The walls are post-tensioned and the joints between the panels sealed using a specially-designed grout that is pumped between the precast-concrete wall slabs.
This grout has been designed to reach a compressive strength of 86 MPa within four days and to further react when it comes into contact with water when the reservoir is being filled to ensure water tightness.
About 6,6 km of PVC post-tensioning ducts and cables were installed between the 64 panels before pumping could commence.
Three-dimensional printed components secure the rubber cast that served as the temporary shutter for the grout.
They were designed and manufactured internally by Corestruc’s own in-house engineering team, CoreEngineering.
Mdingi says that it took just more than a full working shift to fill all of the voids with grout using two concrete pumps, and consideration has been given to this lengthy process in the sequencing of works at the second reservoir site.
Incorporating all of this learning will enable Monde Consulting Engineers & Project Managers and Corestruc to construct the second structure in Bundu in as little as six months versus a year using conventional in-situ methods.
Moreover, important experience gained at this construction site has provided Corestruc the opportunity to further streamline the manufacturing process, which includes the use of specially-designed forms that were imported to ensure the precise manufacture of the precast-concrete wall panels.
Significant experience and learning was also gained in the manufacture of the forms used to produce the complex buttresses that reinforce the wall structure.
Many hours were invested in the design of these concrete elements, which contain numerous cast-in components that were manufactured in-house using computer-numerically controlled machines.
Corestruc worked alongside Gaby Construction, the main contractor which built the reservoir floor and bases that receive the precast-concrete roof structure, as well as the pipeline.
A further benefit of this modular approach is that only representatives of Corestruc’s skilled team work at heights to assist in maintaining an injury and fatality-free construction site.
Certainly, the rapid installation of the roof structure, comprising precast-concrete columns, beams and hollow-core slabs, bears testament to the skills and capabilities of its team, which achieved tolerances of 20 mm at heights of up to 10 m.
Mdingi says that he is proud of his involvement in yet another innovative Monde Consulting Engineers & Project Managers project.