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| High-density polyethylene (1.5mm exposed) |
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Pages in this section include:
| Description |
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Refer High-density polyethylene (2mm exposed).
| Experience |
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Refer High-density polyethylene
(2mm exposed).
This IAL project trialed 200m of 1.5mm exposed HDPE at the Dawhilly
Main Channel by Murray Irrigation Limited in 2001.
| Site
preparation |
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Subgrade preparation required:
- Channel reprofiling to form a consistent
channel profile.
- Subgrade preparation to remove silt and debris.
- Prevention
of regrowth by chemical suppressants.
Despite careful
use of excavators to prepare the subgrade, clods of earth remained
in the channel profile. These were removed
by hand, although rolling of the subgrade can achieve the desired
effect.
| Installation |
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Method of installation
Installation of the 200m section occurred over three days in July
2001.
The material was delivered to the site in large rolls. The HDPE
liner was rolled out and laid across the channel with sections
overlapping to enable welding of joins. A crew of six was required
to lay the material across the channel.
The liner was anchored in trenches along the channel bank and the
end treatment utilised geosynthetic clay lining (GCL).
Specialised equipment
A spool bar was used to lift the HDPE material and provide the
means for laying it across the channel profile. Specialist welding
equipment was also used.
Installation issues
Site access was good and the installation was performed without
any major difficulties.
Figure
1 Completed channel with HDPE
Figure 2 Fencing requirement - low friction is a
hazard for animals
Weather
considerations
Wet and windy conditions on the day that the installation occurred
would have slowed the installation process.
| Durability |
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The lifespan of exposed HDPE is estimated to be 20-40 years.
| Seepage
reduction |
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The baseline seepage rate at the trial site was 4.8L/m2/day.
Post-remediation pondage tests identified seepage rates of 1.1L/m2/day
in 2002 and 15.2L/m2/day in 2003. The first year saw a
reduction in seepage of 77%. The results from the 2003 pondage tests
are questionable
as inspections of the liner showed no holes or tears. A different
location of the pondage test bank, potentially exposing an unlined
section of channel, is thought to be one explanation.
| Cost |
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A breakdown of the costs is presented in the table below. The
total lining cost of $41,083 (2001), or $13.69/m2,
is based on a supplied surface area of approximately 3000m2.
Table 1 Breakdown of costs for HDPE (1.5mm)
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Item
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Cost ($)
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Cost ($/m2)1
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Site preparation (excavator, grader, etc.)
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$1,606.00 |
0.54 |
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Materials (inc. delivery)
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$21,000.00 |
$7.00 |
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Installation (contractor joining)
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$4,000.00 |
$1.33 |
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Backfilling (excavator, etc.)
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$8,400.00 |
$2.80 |
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WMW staff wages, on-costs, etc.
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$3,502.00 |
$1.17 |
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Fencing
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$3,875.00 |
$19/m |
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Miscellaneous
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$100.00 |
$0.03 |
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TOTAL
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$41,083.00 |
$13.69 |
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1. Cost per square metre based on supplied material of 3,000m2.
These costs are indicative of a commercial
application. However, some costs may reduce
as economies of scale are achieved in earth
works, material delivery and installation, utilisation of staff,
fencing, etc. These costs are exclusive of GST.
| Advantages
and disadvantages |
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Advantages
- The supplier’s crew was able to lay the 200m
of material in half a day. The joining of sections by
welding was also completed within half a day. The crew
had a high degree of expertise and experience in laying
the material, and site conditions were favourable.
- A stringent
QA system was used to test the integrity of all welded
seams and produce a record of the quality
of each seam. Such a system, while an additional cost,
is recommended in all installations to test and document
the quality of field seaming procedures.
- Installation
was successful in cold and damp conditions. Welding
would be have been difficult in wet conditions.
Disadvantages
- HDPE can easily puncture, so subgrade preparation
is critical.
- Wet or windy conditions can delayed installation.
- Installation
can be performed relatively quickly, but requires the
mobilisation of a sufficient crew.
Six people
and specialised equipment were needed in this case.
- The
sections completed were both straight, with no protruding
structures, etc. Bends would require material
to be cut
specifically on site, and welded to the shape of
the bend. This would cause some delays.
- Fencing is required
to prevent damage from animals. Fencing also reduces
the risk of animals drowning
as the surface
of the HDPE is extremely smooth and slippery when
wet and prevents animals from escaping.
| Related
pages |
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Flexible membrane lining
techniques
Flexible
membrane materials
Covered liners
High-density
polyethylene (0.75mm)
Geosynthetic
clay liners
Exposed liners
High-density
polyethylene (2mm exposed)
Linear
low-density PE and very low-density PE
(1.5mm)
DamSeal
Unreinforced
polypropylene (1mm)
Unreinforced
polypropylene (0.75mm)
Reinforced
polypropylene (1.1mm)
Butyl
rubber
Asphalt |
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