Construction World May 2015

DAMS AND RESERVOIRS

EnviroFix was laid to prevent dam leaks.

One year later and the dam is retaining water as it should.

SOLUTION FOR LEAKING KZN DAM On a farm in the scenic Nottingham Road area in the heart of the KwaZulu-Natal Midlands, Kaytech’s EnviroFix was specified to provide a cost-effective solution to a leaking farm dam. >

experience with EnviroFix, by following Kaytech’s installation guidelines, successfully installed 4 000 m 2 of non-conformance (NC) EnviroFix X1000. The work was successful and was carried out at a fraction of the cost compared with that of repairing the wall mechanically. No specialised equipment was required. Non-conformance Envirofix is a byproduct of Kaytech’s stringent manufacturing quality control programme. It does not meet the strict specification needed for critical applications such as composite landfill liners or hazardous material confinement, however, it is more cost-effective for a farmer or private individual to use as it is sold at a discounted price. The permeability is low enough to use in farm dam/ water confinement applications. EnviroFix not only provides exceptional liquid containment, but is also ideally suited for use in composite landfill liners and caps, and as a secondary containment barrier in aboveground impoundments. Sixty-six KV power lines in close proximity to some sections of the pipeline required special consideration due to the likelihood of high corrosion risk due to induced currents in the pipeline walls. Specialist surveys were undertaken and a solution was designed and implemented, which comprised the application of alter- nating current mitigation. Conclusion The Dikgathlong Dam and Pipeline project was designed and constructed for Botswa- na’s Department of Water Affairs to meet an ever-growing demand for water due to increased mining and industrial develop- ment activities – both major contributors to Botswana’s economy – as well as supplying potable water to an expanding population in eastern Botswana. The project presented the team with several challenges but construction was completed on schedule and within the allowed budget, and the dam water level has reached full supply level within the last few months.

Besides being used for irrigation purposes, the dam on White Rocks Farm is also used for leisure activities. The dam wall, which had recently undergone repairs after a previous repair failure, was once again leaking. The farmer needed an effective, economical solution that would not entail costly earthworks or imported materials. After inspecting the farm dam, Kaytech’s Paul Lombard suggested that the geosynthetic clay liner (GCL), EnviroFix, with its simple instal- lation, would alleviate the problem. EnviroFix, a proudly South African product manufac- tured by Kaytech, is produced by needling a uniform layer of sodium bentonite between two durable, outer layers of geotextile. Sodium bentonite is a naturally occurring clay mineral with a structure comprising charged platelets. The intake tower is accessed from the crest of the dam embankment by means of a 61 m long steel bridge. Pipeline Delivery of raw water from the dam to the junction with the North-South Carrier Pipe- line is via a new 2 MW pumping station, and a 75 km long welded steel pipeline. Given that flows and pressure of water entering the North-South Carrier need to be continuously synchronised with those within that existing pipeline, a flow and pressure control chamber was designed, which operates in tandem with variable speed flow pumps in the new pumping station, controlled from the flow control chamber via a fibre optic link along the raw water pipeline. The Dikgatlhong pipeline is a 1,2 metre diameter welded steel pipe line and comprises: • Forty-four scour valve installations • One hundred and forty six air valve installations • Four pigging stations

When it comes into any contact with moisture, it swells considerably, and when this occurs under confinement, as in EnviroFix, it forms a lining with such low permeability that it is equivalent to that of approximately one metre of compacted clay. The needle-punching process in the manu- facture of EnviroFix reinforces the otherwise weak sodium bentonite, thereby producing a completely uniform geosynthetic clay liner. The Thermal Lock process in its manu- facture is used to modify and permanently lock the needlepunched fibres into place, resulting in unique properties such as increased internal shear resistance and long term creep resistance. A local contractor, Grevin Price of Ibhu- ngezi Technical Services, who has had • One feeder tank for transient pressure control purposes. • A flow control chamber • A meter chamber • Three river crossings The pipeline is coated with a three-layer PE (3LPE) system. While this involves a marginal increase in coating system cost, the higher level of mechanical and corrosion protection provided by the 3LPE system can significantly reduce the whole-life unit delivery costs. The Department of Water Affairs demanded a high level of protection for this critical pipeline and a technical specification based on the Canadian CSA Z245.21 pipe coating standard was used. The internal lining consists of a two component solvent free polyamine cured epoxy coating. The pipes were welded using gas shielded Argon root welding by suitably qual- ified and certified welders. The pipes were placed in the trenches onto specially manu- factured pedestals to allow for welding and coating of the joints.

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CONSTRUCTION WORLD MAY 2015