Rehabilitation of Clifton Avenue Reservoir

(Urban Management, Jan./Feb. 2000)

Synopsis

The 14 Mℓ Clifton Avenue reservoir is situated in a dolomitic area in Centurion near Pretoria, South Africa. The cylindrical prestressed concrete reservoir with a domed roof was constructed in 1971. The reservoir wall is free-sliding and is supported on a bearing located on the wall footing.

In  May 1997 the reservoir started to show signs of leakage. Remedial work to the waterproofing bandages on joints in the reservoir done by the Greater Pretoria Metropolitan Council (GPMC) proved unsuccessful. At first filling of the reservoir after rehabilitation of the bandages leakage was detected on the outside of the reservoir at the wall-to-floor joint, indicating settlement of the floor slab and wall footing. GPMC then appointed a consulting engineering company, BKS, to resolve the problem. Erhard Kruger and Emuël Kok, who at the time were employed at BKS, were responsible for the design of the remedial measures. Erhard Kruger was responsible for the structural remedial work and Emuël Kok for the geotechnical rehabilitation.

Successful rehabilitation was dependent on an accurate diagnosis of the cause of the problem and assessment of the geotechnical conditions. Monitor points were installed on the wall footing and movement at these points were monitored over a period of 18 months. The floor slab of the reservoir was also surveyed. Gradual settlement of up to 196 mm occurred over about 25% of the floor area. Cracks also appeared in the ground surface around the reservoir. The settlement caused the bandage between the wall and floor to tear in this area. Eventually a gap of 250 mm formed beneath the settled floor slab, which rendered the reservoir unserviceable.

Dynamic cone penetrometer tests were conducted and boreholes were drilled inside and outside the reservoir to assess the geotechnical conditions.

Erhard Kruger and Emuël Kok discuss how this reservoir was successfully rehabilitated in an article which appeared in Urban Management Volume 31 of January/February 2000. Click the link to download the complete article.

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(Article reproduced with the permission of the publisher, TE Trade Events; www.tetradeevents.com)