Saving a doomed reservoir- Rehabilitation of Waterval Reservoir

(The Structural Engineer, 2 Jun. 2010)

Synopsis

The Waterval reservoir, with a capacity of 45,5Mℓ is situated in Florida, Roodepoort, a suburb of Johannesburg, South Africa.  Structural drawings are dated 9 February 1953, suggesting that the reservoir was constructed during 1953 and 1954.  The reservoir is owned and operated by Rand Water, who supplies potable water to Pretoria, Johannesburg and surrounds.

The reservoir is cylindrical and has a gravity type mass concrete wall and reinforced concrete floor, roof and columns. The wall has a complicated section, and only the top 1,1 m is reinforced. The roof slab is supported on the wall and 120 circular columns.

The reservoir is surrounded by an earth embankment, the level of which is approximately 1 m below the top of the reservoir wall. Due to the slope of the terrain, the height of the fill varies along the perimeter, with the embankment being at its highest on the southern side of the terrain, where the reservoir is at its closest to the residential area.

During the nineties large cracks developed in the reservoir wall. With time, the width of these cracks increased, resulting in some of the cracks being up to 20 mm wide. Various unsuccessful attempts were made to seal these cracks with sealants and bandages.  Eventually the reservoir had to be de-commissioned in 2001 due to excessive leakage and concerns regarding the structural integrity of the reservoir especially since the largest cracks in the wall were occurred closest to the residential area.

In May 2006 Rand Water called for tenders and proposals to rehabilitate the reservoir, and Nyeleti Consulting, with HGK Consulting CC as specialist sub-consultant, was awarded the tender.

Erhard Kruger of HGK Consulting CC and Marelize Mostert of Nyeleti Consulting discuss how this reservoir was successfully rehabilitated in an article which appeared in The Structural Engineer of 2 June 2010.

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