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CONSTRUCTION WORLD
MAY
2015
DAMS AND RESERVOIRS
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.
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
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.
>
EnviroFix was laid to
prevent dam leaks.
One year later and the dam is
retaining water as it should.
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.
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
• 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.
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.