Nov 25, 2011
De Hoop to begin collecting water in JanuaryBack
Construction|Aggregate|Ash Resources|Cement|Concrete|Diesel|Flow|Pipe|Pipes|PROJECT|Resources|Road|Safety|Screens|System|Water|De Hoop Dam|Cement|Equipment|Flow|Pipes|Products|Transport|Transportation Disruptions|Work Site|Environmental|Mike Nitzsche|Water|Pipe|Diesel
© Reuse this
The dam wall will be around 85 m high after completion, scheduled for October next year, and had reached half its final height in early November. The 1 010-m-long Department of Water Affairs project is under significant environmental monitoring and will pump water past the wall to ensure that the river does not run dry, even for a moment, to preserve downstream ecologies and communities once it seals the river outlet.
The dam wall will contain around 1.125-million cubic metres of concrete of which 90% consists of Roller Compacted Concrete (RCC). The downstream wall rises in 1.2-m-high steps with the upstream side being vertical. The hourly pouring rate of the team is around 230 m3/h, with spurts of around 360 m3/h.
The De Hoop Dam team is currently embarking on an effort to improve the previous South African RCC placing record, which consisted of 103 000 m3 of RCC placed in one month (23 days), also achieved by the De Hoop Dam Team during November 2010.
The wall comprises roller compacted concrete composed of cement, fly ash, 38 mm stones, 19 mm stones and sand, with retarder or plasticiser added as needed and without grout. Further, the faces of the steps are immersion vibrated. This removes the need to use a concrete skin against the shutters, which are oiled instead, providing a smooth finish with high strength, he explains.
Articulated dump trucks (ADTs) transport the concrete onto the dam wall, where it is spread out by a bulldozer into a 300-mm-thick layer and compacted by a 10 t vibratory roller.
Quality control is of high importance and the team continuously tests the compaction of the concrete and also sends samples to be tested in a laboratory.
The dam wall will narrow to a final width of about 10 m at the top and concrete will be delivered to the work site by a conveyor system designed to transport concrete up to 60 m high, when trucking is no longer efficient. The conveyor system will, however, feed the concrete onto an ADT on the wall, which will then place it on the right spot.
Mist sprayers saturate the air over the work site to prevent the concrete from drying out. The addition of a retrader product (additive) to the RCC enables the contractor to place RCC over a large area and continue with a 24-hour, 7-days-a-week placing operation without running the risk of encountering “cold joints”.
Five concrete batching plants work nonstop to provide a total of around 300 m3/h of concrete. Thirty to 35 tanker loads a day (12 hour) of fly ash are transported to the site and fed into silos that act as a supply buffer in case of transportation disruptions. Fly ash products company Ash Resources’ Matla plant in Mpumalanga is about 320 km from the De Hoop site, with Ash Resources Lethabo plant in Free State functioning as back up to manage the high fly ash demand.
The project, with the current RCC placing program, consumes between 15 000 and 20 000 l/day of diesel, costing around R5.5-million each month. A complete maintenance programme of all plant and equipment is being followed to ensure minimum downtime.
Extensive foundation grouting has been completed to ensure the closing off of any fissures and openings in the rock foundation that may cause leaks under 80 m of water pressure.
Quarrying on site is complete and the rising dam will eventually inundate the quarry site, which is around 30 m deep. All of the required aggregate products has been produced and is stored above the partial impoundment level. The aggregate sub-contractor has already de-mobilised and rehabilitation work of the quarry is nearly complete.
The dam outlet structure contains staggered 2-m-diameter outlet pipes to release water at different dam levels and to select required water quality. The pipe inlets are protected with trash racks and fine screens, to prevent debris from entering the pipes. Large butterfly valves are used to regulate the flow of water through the two 2-m-diameter water abstraction pipes.
A section of the provincial road P169-1 (R555) between Middelburg and Burgersfort will be submerged by the dam and requires realignment. The realigned route of about 20 km will pass the new dam on the western side and includes two bridges over the Steelpoort river.
Since work is conducted at heights, great emphasis is placed on safety and the safety of the workers.
Further, once a shift, all the machines are hosed down to remove concrete build-up that could cause a fault or failure when it hardens.
Edited by: Martin Zhuwakinyu© Reuse this Comment Guidelines (150 word limit)
Other Construction Materials News
Specialised construction products supplier a.b.e. Construction Chemicals Chryso Southern Africa Group has expanded its range of Germany-based industrial adhesive and coatings systems provider Voelkel Industrie Produkte (VIP) polyurea coatings to include systems for...
Recent Research Reports
Road and Rail 2014: A review of South Africa's road and rail infrastructure (PDF report)
Creamer Media’s Road and Rail 2014 report examines South Africa’s road and rail transport system, with particular focus on the size and state of the country’s road and rail network, the funding and maintenance of these respective networks, and the push to move road...
Real Economy Year Book 2014 (PDF Report)
This edition drills down into the performance and outlook for a variety of sectors, including automotive, construction, electricity, transport, steel, water, coal, gold, iron-ore and platinum.
Real Economy Insight: Automotive 2014 (PDF Report)
This four-page brief covers key developments in the automotive industry over the past 12 months, including an overview of South Africa’s automotive market, trade figures, production and the policies influencing the sector.
Real Economy Insight: Construction 2014 (PDF Report)
This five-page brief covers key developments in the construction industry over the past 12 months. It provides an overview of the sector and includes details of employment in the sector, infrastructure and municipal spending, as well as insight into companies’...
Real Economy Insight: Electricity 2014 (PDF Report)
This five-page brief covers key developments in the electricity industry over the past 12 months, including details of State-owned power utility Eskom’s generation activities, funding and tariffs, independent power producers and prospects for the sector.
Real Economy Insight: Road and Rail 2014 (PDF Report)
This six-page brief covers key developments in the road and rail industries over the past 12 months, including details of South Africa’s road and rail network and prospects for both sectors.
This Week's Magazine
While Ekurhuleni-based transformer manufacturer Reliable Transformers currently designs, manufactures and tests its products according to the SANS 780 specifications for distribution transformers and other applicable transformer specifications, it is working towards...
Global endpoint security solutions company Kaspersky Lab has introduced new measures to prevent cyber criminals from accessing sensitive data, alongside its malware-signature and heuristic device analysis detection methods. Threats to mobile devices have increased...
To ensure uptake and a positive impact, Wireless Fidelity (Wi-Fi) networks in cities must be provided at schools, community centres and commercial centres to enable citizens and government to access information that will improve access to and delivery of services....
Eco-estate Monaghan Farm, located near Lanseria airport, north-west of Johannesburg, has taken a new approach to modern living and sustainability with its 517 ha development, dedicated to farm living.
Forklift and lift-truck distributor Goscor Lift Hi-Reach launched the Genie SX-180, the tallest self-propelled super boom in Africa, in Johannesburg last month. “As the official distributor of the well-known Genie range of equipment in Southern Africa, we are pleased...