Most canals with concrete linings have joints at regular close intervals to control cracking of the concrete due to shrinkage and thermal movements. Whereas such canals are usually taken out of service for regular maintenance of the joint sealants, the Zulkerbosch canal was designed to operate continuously. The concrete lining was therefore designed to have no joints at all, with the size and spacing of the cracks controlled by high tensile steel wire reinforcement In accordance with the then newly published British Code BS 5337 for water retaining structures.
The Zuikerbosch canal was required to be a high security canal designed to operate continually without down-time for maintenance. It was therefore necessary to take steps to ensure that the highly expansive slickensided clays encountered along the canal route would not produce differential soil movements sufficient to damage the thin concrete lining of the canal.
The 500 Ml terminal reservoir (forebay) at the end of Ihe Zuikerbosch canal presented a number of challenging design problems. The forebay is utilized as balancing storage between the Zuikerbosch Canal and the Rand Water Board's large water treatment plants. The problems derived from the shallow water depth and from the embankment foundations which comprised collapsing aeolian sands overlying permeable and active alluvial clays.
The Zuikerbosch canal is a good example of the difficulties that are experienced in establishing the grass needed to counter soil erosion and to heal the scars left on the landscape by civil engineering activities.
High velocity water jets discharged continuously from radial gates into the stilling basins at the Zoekfonteln pipeline control works create conditions conducive to cavitation. Sources of cavitation are primarily roughtness on the concrete walls and floors of the chutes leading Into the stilling basins, and shear zones between fast moving and slow moving water in the hydraulic jumps in the stilling basins. Cavitation from the first source was minimized by the use of special formwork to provide ultra-smooth concrete surfaces, but these measures could not be expected to be entirely successful, so aeration was also Introduced.
The Zuikerbosch canal incorporates two cast in-situ concrete inverted siphon pipes, with a tear-drop cross section about 6 m high and lengths of 520 m and 390 m, respectively. Using a travelling form 12,5 m long, the contractor building the siphons needed a three day turn-around time in order to complete the work within a tight construction schedule.