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| Unreinforced polypropylene (1mm) |
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| Description |
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Polypropylene (PP) is produced in both unreinforced and reinforced
form to provide a choice in terms of tensile behaviour.
The unreinforced membrane is typically very flexible with excellent
elongation capabilities, but the reinforced membrane has low thermal
expansion properties. Its flexibility is similar to PVC, enabling
prefabrication into panels of several thousand square metres.
Polypropylene has a quite good resistance to common chemical exposures,
excellent mechanical properties and excellent UV performance when
the polymer is properly stabilised. It is sometimes referred to
as FPA (flexible polypropylene alloy). Reinforced and unreinforced
polypropylene have UV and chemical resistance properties approaching
those of HDPE.
Polypropylene is ideally suited for applications requiring long
life in harsh conditions, particularly where substrate stability
cannot be assured. Its puncture resistance makes it suitable for
applications where a smooth substrate surface cannot be prepared.
| Experience |
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Common polypropylene applications include floating covers, landfill
liners and caps, tank liners and sewage processing ponds. No literature
reporting its effectiveness has been found, but the manufacturer
estimates a useful life of 20 years.
Unreinforced polypropylene (PPU) (1mm) was trialed in 200m of the
Dahwilly Main Channel by Murray Irrigation Limited in July 2002.
| Site
preparation |
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Subgrade preparation required:
- Channel reprofiling to achieve consistent batter slopes and
minimal protrusions.
- Silt and clod removal.
| Installation |
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Method of installation
Installation occurred during July 2002. Approximately two days
was required for the installation.
The liner material was supplied in large roll 6.5-7.0m wide.
To lay the PPU across the channel profile, a crew of four was
required to pull the material from the roll across the channel.
Two additional crew members were required to weld sections together.
The PPU channel section had a small curve, which was accommodated
by the material. However, a stock fence (installed across the
channel in the previous year to exclude stock) was in the way.
Careful installation was required around the posts on the channel
bank, cutting and rejoining the liner.
The liner was anchored in trenches along the channel bank and
the end treatment utilised geosynthetic clay lining (GCL).
 Figure
1 Welding the PPU sheets together
 Figure
2 PPU channel section near completion (LLDPE is in the background)
Specialised equipment
Material spool and joining equipment.
Installation Issues
There was some evidence of material being damaged either during
shipping or transport to the site, but this did not cause significant
problems.
The material spool used for other liners did not fit the rolls
of PPU, so makeshift rollers using lengths of steel pipe were
used. This was not satisfactory because the pipes kept sliding
out when unrolling the material. As a result it was decided to
roll the material out along flat ground, cut it to the required
length, and then drag the section into the channel.
Weather
considerations
There were high winds during installation and difficulty in laying
the material slowed the process significantly, causing sheets to
move during the welding process.
| Durability |
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The manufacturer estimates a useful life of approximately
20 years.
| Seepage
reduction |
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The baseline seepage rate at
the PPU site was 7.8L/m2/day.
A pondage test in 2003 identified
a seepage reduction of 94% (to
0.5L/m2/day).
| Cost |
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A breakdown of the costs is presented in the following table. The
total lining cost of $46,114 (2002), or $15.37/m2, is based on
a supplied surface area of 3,000m2.
Table 1 Breakdown of costs for PPU (1.0mm)
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Item
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Cost ($)
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Cost ($/m2)1
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Earth works (excavator, loader, etc.)
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$3,806 |
$1.27 |
| Materials |
$23,499 |
$7.83 |
| Delivery |
$2,500 |
$0.83 |
| Installation |
$9,907 |
$3.30 |
| MIL staff wages, on-costs, etc. |
$5,015 |
$1.67 |
| Fencing |
$1,138 |
$5.69/m |
| Misc. |
$ 249 |
$0.08 |
| TOTAL |
$46,114 |
$15.37 |
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1. Cost per square metre based on 3,000m2 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. The costs are exclusive of GST.
| Advantages
and disadvantages |
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Advantages
- Despite some unfavourable
conditions in the form of wind and a wet subgrade, installation
of PPU was considered to be quite straightforward.
- PPU
could be installed on a curved section of channel,
and although requiring care, was installed around posts
on the channel bank, involving cutting of the liner and
subsequent welding.
Disadvantages
- PPU is not suited to installation under windy conditions,
as this makes it difficult to lay the material and can
cause the sheets to move during welding.
- Wet subgrade
conditions can interfere with the welding process.
- Exposed
installations require fencing to prevent risk of damage
by animals.
| 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)
High-density
polyethylene (1.5mm exposed)
Linear
low-density PE and very low-density PE
(1.5mm)
DamSeal
Unreinforced
polypropylene (0.75mm)
Reinforced
polypropylene (1.1mm)
Butyl
rubber
Asphalt |
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