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| Flexible membrane lining techniques |
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Pages in this section include:
Refer to Table 1 Channel seepage remediation decision
matrix for
a summary of flexible membrane lining techniques. Flexible membrane
liners are thin, flexible, impermeable liners, which, combined
with the strength of the base soil, can be used to reduce seepage.
The geomembrane is a thin impermeable barrier of synthetic material
that offers very little structural capacity. They rely on a properly
constructed subgrade and careful installation to provide optimum
results.
There are two ways to install flexible membrane liners:
- Exposed:
The membrane is simply placed on the subgrade of the channel.
The material is exposed to weathering and physical damage.
- Covered:
The membrane is covered with a non-erosive material that
protects the membrane from weathering and physical damage.
Protection from ultraviolet damage greatly expands the number
of suitable materials compared to an exposed installation.
Cover materials
typically include 300-500mm of soil, or 50-100mm of concrete.
A wide variety of synthetic liners is available, and new
products are continually emerging. The discussion in this
section does
not cover every liner available.
| Properties |
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In addition to being impermeable, other desirable properties
of flexible membrane liners are:
- The material should not be a source
of any hazardous substances either from the base material or
secondary materials such as bonding
agents, adhesives or cleaners.
- The liner should meet water quality
requirements if used for potable water.
- If the material
is exposed, it should offer appropriate weathering
performance and withstand chemical and
environmental exposures.
- The material should be
capable of reliable fabrication using semi-automatic
welding practices, which produce seams
that match
the basic tensile properties of the material.
- It should
be possible to weld and seam the material for repairs
after many years of service.
| Installation |
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Site preparation
Subgrade preparation required:
- The channel must be drained.
- A fairly uniform profile
enables the membrane to be installed more easily,
avoiding pressure points and the need to shape the
membrane around irregularities.
- If the slope is greater than
1:1, provision has to be made for personnel access
into the channel for safe installation
without
causing damage to the lining material.
- Sharp stones, debris
and vegetation should be removed from the channel
surface.
- Chemical sprays can be used on the banks to
prevent vegetation regrowth, which may penetrate
the lining
material.
Method
Prefabricated flexible membrane liners are typically installed
using a fabric spool or spreader bar mounted on a crane or excavator.
Individual sheets of the liner are joined together in-situ or
prefabricated. The liner is secured in the channel bank with
an anchor trench.
The alternative to prefabricated liners are those which are constructed
on-site, such as applications of bituminous rubber over a geotextile
fabric.
Weather considerations
Flexible membrane liners can be installed in most weather conditions,
but the following points should be considered:
- Wind can impede laying the membrane.
- Low temperatures, excess
moisture and shade can slow down drying and bonding processes.
- High
temperatures during installation cause expansion of the
liner, possibly placing stresses on the material
and the joins
when the liner shrinks upon cooling.
| Related
pages |
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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 (1mm)
Unreinforced
polypropylene (0.75mm)
Reinforced
polypropylene (1.1mm)
Butyl
rubber
Asphalt |
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