Fast-tracking bulk water delivery

Tango’s Consultants has helped devise a unique means of accelerating the completion of two new reservoirs in the City of Ekurhuleni. The method also ensures a high-quality final structure and provides construction cost savings.

The structures for the reservoirs are being prefabricated in a controlled factory setting far removed from the many variables encountered on a traditional construction site. This passes on savings in terms of formwork and staging, in addition to reinforcement bar and concrete. Guaranteed precision by the manufacturer and installer of the system has also eliminated the risk of wastage due to errors on-site.

The precast concrete reservoir systems are being manufactured and erected by Corestruc as the specialist subcontractor, working alongside principal builders Anita Building and Selby Construction, for the Pam Brink and Selcourt projects, respectively. The works form part of the Ekurhuleni Water and Sanitation Department’s strategy to significantly strengthen water supply to these rapidly developing areas.

The new 30 Mℓ reservoir in Selcourt will bolster the existing 11.4 Mℓ of water storage capacity and sustain new and planned large developments, including a megacity in the larger Springs area.

In Pam Brink, a 25 Mℓ structure is being constructed to strengthen available supply from a 11.4 Mℓ reservoir. Existing bulk and distribution water infrastructure in this expanding area of Ekurhuleni has also come under extreme pressure over the years.

The ring-beam supports the wall panels and is being built by an emerging contractor who is also being trained by the principal contractor and Corestruc

The centre portion of the roof structure is constructed first and the wall as well as the floor slab are constructed next

Both projects are 18 months in duration, with the reservoir in Selcourt due for completion by the end of this year, and the other in Pam Brink by the beginning of 2021, despite the Covid-19 lockdown and other extenuating circumstances that halted operations for periods.

Certainly, this bears testament to the ability of the unique system to significantly accelerate the construction of reservoirs, which are notoriously complex and timeconsuming to build. Up to five months have been shaved off the works programme by enabling the construction of the floor, walls and roof simultaneously.

Using conventional construction methods, only two trades would have overlapped. These include the construction of the wall, a complicated undertaking that demands absolute precision to ensure water-tightness. This slow and meticulous process is followed by the construction of the roof, which entails erecting and installing tonnes of scaffolding and formwork inside the structure.

The precast concrete system has enabled the professional team to significantly fast-track construction

Local innovation and design excellence

Andrew Singosho, structural engineer, Tango’s Consultants, has worked with Corestruc on another reservoir project for the Water and Sanitation Department, and introduced his consulting engineering firm to the modular reservoir system.

Singosho was also responsible for adapting the design to these two projects, which initially incorporated in situ construction techniques that possibly would have delayed delivery of the infrastructure.

“In reviewing its design to ensure that it was structurally sound, I was impressed by the extent of local innovation that has gone into the system and believe that there is potential for wider deployment of the technology in the country. This is considering the need to significantly accelerate the roll-out of water infrastructure in South Africa, especially in outlying areas that are not adequately serviced by readymix operations. Transporting readymix over long distances and poor road infrastructure in these areas is a significant risk, while batching concrete on-site requires strict quality control measures that would possibly delay projects,” Singosho says.

Assembly and sealing

Corestruc’s system comprises prefabricated wall panels and buttresses that are used to reinforce the structure and, notably, uses both vertical and horizontal tensioning to resist applied forces. The structure is sealed using a special grout that has been designed to reach a compressive strength of 100 MPa within four days and further react when it comes into contact with water, when the reservoir is being filled. It is pumped through temporary shutters around the circumference of the reservoir in a controlled manner after the installation of kilometres of post-tensioning ducts and cables. Meanwhile, the roof of the reservoir comprises precast concrete columns, beams and hollow-core slabs, which are stitched together to create a single monolithic structure.

At both construction sites, the centre portion of the precast concrete roof was completed first to enable the main contractors to start constructing the ring beam that supports the wall panels. The roof will be completed once the walls have been constructed as part of the final phases of the projects, while work on the floor slab will proceed during the installation of the walls.

These precast concrete elements are dispatched to site from the factory on a just-intime basis. They are lifted and placed directly from the truck trailers using a mobile crane as they arrive, with the first panel supported by props that are removed once it has set, to enable the remaining slabs to be placed against the other to complete the wall. By mitigating the use of propping, Corestruc ensures that it frees up space to enable work to continue unhindered.

As is the case with the roof of the structure, state-of-the-art survey equipment is used to precisely install each panel, maintaining tolerances of about 5 mm throughout the process. The holes at the bottom of the wall panels perfectly align with the bolts grouted into the ring beam, as well as the steel plates at the top with the voids in the adjacent slabs. At the same time, the voids that traverse the full width of the panels through which the posttensioning strands are threaded also align. Each precast concrete element has a compressive strength of up to 70 MPa and is accompanied by its own technical drawing and documentation. This includes detailed specifications and a thorough account of the pre- and post-inspections before being dispatched to the construction sites.

Certainly, the high quality levels achievable in a factory setting were also a major selling point for Corestruc. Representatives of Tango’s Consultants also visited one of the company’s factories and completed reservoirs in Mpumalanga to witness for themselves the high quality of the company’s workmanship.

Labour-based construction elements

Despite the extensive use of prefabricated concrete on these two projects, the professional team has been able to meet all its socio-economic targets on these Expanded Public Works Programme (EPWP) projects.

“While the specialist work has been outsourced to Corestruc, there has been ample opportunity to deploy labour-based construction methods to create employment opportunities for members of surrounding communities. This includes the earthworks, as well as the construction of the ring-beam and in situ concrete floor slab and column footings. These are complemented by the employment prospects created at Corestruc’s factory. Notably, they are long term in nature and provide greater opportunity for skills development in the construction sector than is possible under the EPWP,” says Kadiebwe Mulunda, civil engineer, Tango’s Consultants.

As the system continues to gain traction in the country, Mulunda adds that more sustainable and skilled jobs will be created in these factories, while there is also significant potential to train emerging contractors to install the system on smaller reservoir projects. This is in line with government’s SMME development policies in the construction sector.

Willie de Jager, managing director of Corestruc, concludes that he is proud of his company’s involvement with Tango’s Consultants, which is known for the high quality of its engineering services.