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| Description |
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DamSeal is a bitumen sealant designed to prevent seepage losses.
It was developed by Tosas (Pty) Ltd in South Africa as a water
conservation aid for farmers. Initial trialling of the product
commenced in 1989, but the current DamSeal formulation was not
developed until 1996.
The DamSeal concept involves the in-situ application of a mineral-filled,
rubberised bitumen emulsion to an approved geotextile fabric liner.
The geotextile is laid in the channel bed fitted to the prepared
channel base and walls and anchored to the top of the channel wall.
The geotextile panels are joined together using the bitumen emulsion
before being coated in three applications of various dilutions
to form a reinforced, continuous ‘bitumen rubber’ liner.
The DamSeal emulsion impregnates the geotextile and forms a waterproofing
lining of the channel floors and walls, preventing seepage and
potential wall failure. The DamSeal liner is repaired using DamSeal
in conjunction with a patch.
In South Africa, the installation can be performed manually and
the product is applied by broom, a very labour intensive process.
An alternate installation process involves pumping and spraying
the emulsion to reduce the labour requirement..
| Experience |
|
DamSeal is used extensively in South Africa for lining of channels
and reservoirs. It was trialed in a 200m section of the Dawhilly
Main Channel by Murray Irrigation Limited in 2001.
| Site
preparation |
|
Subgrade preparation required:
- A fairly uniform profile enables the geofabric to be installed
more easily, avoiding pressure points and the need to shape
the fabric around irregularities.
- If the slope is greater than
1:1, provision has to be made for personnel access to the
channel for safe installation without
causing damage to the geofabric.
| Installation |
|
Method of installation
- Install geotextile in lengths across channel and secure
with sandbags.
- Fold back geotextile at join, lay down a seam
of DamSeal compound along each join using a pump and lance
then fold back fabric.
Immediately overspray join with DamSeal.
- Apply the prime coat
then second and third coats using air-atomisation spraying
technique, allowing drying time between coats.
- Secure DamSeal
and geotextile with an anchor trench approximately 400mm
from the inside toe, and 400-500mm deep.
Figure 1 Joining the geotextile sheets
Figure 2 Applying the first coat
Figure 3 Finished channel section
Specialised equipment
- Geotextile is laid using fabric spool or spreader bar mounted
on a crane or excavator.
- DamSeal was applied to the geotextile
using a truck-mounted unit consisting of duplex product mixing
and pumping systems,
air compressor
and accessories. An ‘off-road’ forklift equipped
with ‘drum-grab’ forks
was utilised for manoeuvring the product into hoppers on the
truck-mounted unit.
Weather
considerations
Able to be installed in all conditions, however:
- Wind can impede
laying the geotextile.
- Low temperatures, early morning dew,
residual moisture in the channel and shading of bank(s)
due to orientation of the
sun
particularly during southern winters will slow the drying
process and reduced
the available working time.
| Maintenance |
|
A ‘refresher’ coat of DamSeal above the water line
approximately every 4 years is suggested by the manufacturer. The ‘refresher’ coat
can be applied manually using a broom if specialised equipment
is not available.
The DamSeal liner is repaired using DamSeal in conjunction with
a patch of geofabric.
| Durability |
|
The DamSeal lining system has shown good resistance to weathering
and ageing in numerous installations in southern Africa. The estimated
lifespan in the absence of puncture is 15-20 years, according to
the manufacturer.
| Seepage
reduction |
|
The
baseline seepage rate at the DamSeal site was 4.4L/m2/day. Two
post-remediation pondage tests have been conducted revealing seepage
rates of 2.8L/m2/day (2002) and 0.4L/m2/day (2003). This amounts
to a seepage reduction of between 36-90%. Note that a similar final
result may have been achieved with a channel of considerably higher
baseline seepage.
| Cost |
|
A breakdown of the costs is presented in the following table. The
total cost of $31,812 (2001) corresponds to a lining cost of $10.33/m2 based on a supplied surface area of 3080m2. Costs are exclusive
of GST.
Table 1 Breakdown of costs for DamSeal
|
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Item
|
Cost ($)
|
Cost ($/m2)1
|
|
|
Earth works (excavator, loader, etc.)
|
$1,606 |
$0.52 |
| Materials |
$12,197 |
$3.96 |
| Delivery |
$1,817 |
$0.59 |
| Installation |
$8,715 |
$2.83 |
| MIL staff wages, on-costs, etc. |
$3,502 |
$1.14 |
| Misc. |
$100 |
$0.03 |
| Fencing |
$3,875 |
$19.00 |
| TOTAL |
$31,812 |
$10.33 |
|
1. Cost per square metre based on 3,080m2 of material supplied.
2. Cost per metre of fencing based on 200m section of channel.
Cost for materials and installation are indicative of a commercial
application to a longer section of channel. Other costs would
be expected to reduce marginally as economies of scale in
earth works, delivery, utilisation of staff, and fencing
are achieved.
| Advantages
and disadvantages |
|
Advantages
- Subgrade preparation was not critical, as the geotextile
and application followed the contour of the channel well,
and protrusions were not a great issue.
- The lightweight,
permeable geotextile can be installed relatively easily
in windy conditions.
- The sections completed were both
straight, with no protruding structures. However, because
of the nature
of the material, bends and other obstructions are
not likely to pose significant problems as sections can
be easily cut out and rejoined as necessary.
- DamSeal
is easily bonded to structures and protrusions such
as inlets, outlets and pipes.
- Repair of the punctures
resulting from removal of fill from anchor trenches
was relatively easy.
Disadvantages
- DamSeal is not ideally suited to cold, moist and
wet conditions, as these conditions reduce available
working hours and extend the required time for drying
between coats. However, DamSeal was successfully installed
in the Dahwilly Main channel despite unfavourable conditions.
- Fencing
is required to prevent access and damage from animals.
| Related
pages |
|
Flexible membrane lining
techniques
Flexible
membrane materials
Covered liners
High-density
polyethylene (0.75mm)
Geosynthetic
clay liners
Exposed liners
High-density
polyethylene (2mm exposed)
High-density
polyethylene (1.5mm exposed)
Linear
low-density PE and very low-density PE
(1.5mm)
Unreinforced
polypropylene (1mm)
Unreinforced
polypropylene (0.75mm)
Reinforced
polypropylene (1.1mm)
Butyl
rubber
Asphalt |
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