Reservoir construction delays explained by metro
The metro has recently responded to our media enquiry about the work in progress at the Xhosa/Zulu reservoir.
Tsakane – Themba Gadebe, senior media manager for the city, explains the project was awarded on April 20, 2017, and the contractor started to work on site on May 1, 2017.
“Three weeks later the project was stopped by members of the community who were petrol bombing the contractor’s vehicles and equipment.
“The reasons for such action were unclear but there were insinuations of general disgruntlement that some community members wanted a stake in the project beyond general sub-contracting.”
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He says to this end, the contractor immediately evacuated from the site on the basis of unfavourable working conditions.
“The project was effectively stopped until September 3, 2017, when the issue was resolved with the said members of the community.
“From the design report, as designed by the engineers, the depth of the soil raft was designed at 1.5m below the slab based on the collapsible soil underlying the proposed area for the reservoir.”
He adds that collapsible soil is defined as unsaturated soils that can withstand relatively high pressure without showing a significant change in volume.
“However, upon wetting, they are susceptible to a large and sudden reduction in volume.
“This depth was changed to 2.3m by the engineers as a precautionary measure in view of the confirmed existence of collapsible soils during excavation.”
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He continues to say on October 10, 2017, the engineers further changed the depth to 3.75m because of the continued existence of the collapsible soils.
On October 27 the depth was further changed to 5m.
“Despite the 5m excavation, collapsible soils were still prevalent on approximately two-fifths of the reservoir footprint.
“On December 17, 2017, the engineers, based on the continued existence of these collapsible soils, decided to employ the use of piles for that section of the reservoir underlain by the collapsible soils.”
In December 2017, due to the builder’s break, drilling of piles was shifted to January 2018.
“On January 20, 2018, the engineers decided piling was no longer necessary as per the advice they got from a specialist geotechnical engineer.
“The original completion date was set for February 15, 2018, but due to numerous delays as outlined above it has been shifted to September 28, 2018.”
Explaining what causes the water to run outside the parameters of the site, he says, “Tsakane has received inordinately high rainfall in April and May 2018.
“The engineers always require decanting of any water from the site before any work is done.
“Therefore, every time there is rainfall a lot of pumping is undertaken, hence the water outside the perimeter of the site.
“Furthermore, the area has high water table which also requires continuous pumping.”
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