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| Clay lining example: Waranga Western Channel |
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Pages in this section include:
| Site
preparation |
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Before commencement of clay lining works, the channel was desilted
and banks and batters were stripped to a minimum depth of 100mm
to remove all topsoil, trees and root systems. Where the channel
profile was widened to increase the capacity, channel banks were
reconstructed before lining.
| Installation |
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Design features included:
- 600mm clay lining in bed.
- 600mm clay lining on batters.
- 1:2.5 batter slope.
- 300mm compacted freeboard.
- 150mm protective cover over the
bank crest to minimise shrinkage and dispersion and encourage
grass cover.
Method of installation
Two techniques were adopted for the clay lining:
- A total length of 1,140m of the channel bed was excavated
to 600mm below the design bed level and to a depth of 700mm
perpendicular
to the batters of the channel. Borrow material for the lining,
which was hauled in from a borrow site, was placed in the bed
and batters of the channel in layers of 150mm, and compacted
to 98%
of maximum dry density at ±2% of optimum moisture content.
A 100mm compacted layer of crushed rock was then placed over
the clay lining on the batters to help to maintain a constant
moisture
content in the clay liner, thus reducing cracking and protecting
the liner from erosion. Batter slopes were no steeper than
1:2.5 so that construction machinery could achieve adequate
compaction
of material on the batters.
- A different technique was adopted
for a 1,000m section due to the high shrinkage characteristics
of the borrow material
discovered
during construction. The technique involved using material
from the existing batters, mixing it with both imported clay
and the
degraded sandstone/siltstone from the channel bed using a
stabiliser (large rotary hoe). It required double handling
of material
within the channel profile to enable mixing and then compaction
of the
bed and batters in layers of 150mm up to the 600mm depth.
Only about 10% of the material required was sourced from the
borrow
site.
Figure 1 Aerial View of
clay lining
Specialised equipment
A stabiliser (large rotary hoe) was required to mix imported clay
with the in-situ material over a length of 1,000m.
Figure 2 Stabiliser mixing insitu material with imported clay
Installation issues
Borrow sites were identified on properties adjacent to the channel
and were tested for their suitability for channel lining. Laboratory
test samples were classified as CH material, which is described
as ’inorganic clays of high plasticity‘ in the USCS
classification system. This material has very low permeability
but also has high shrink/swell potential (i.e. prone to cracking)
and low scour resistance. The material was confirmed by as suitable
for clay lining as it was similar to material being used in other
nearby channel lining projects. Due to the high shrink/swell characteristics
of the soil and the scale of the project, a protective layer of
compacted crushed rock was placed over the clay liner on the batters.
During construction, soil tests identified shrinkage properties
at one borrow site as unsuitable for compacted clay lining, and
hence the alternative method was adopted.
At one site the excavation of the channel profile prior to clay
lining exposed a large length of canal. Working ahead to this extent
exposed the area to the elements and so large sections of subgrade
and partly compacted clay had to be trimmed to remove wet clay
from the profile following rainfall.
| Durability |
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The estimate lifespan of clay lining is 30 years, and the presence
of a protective cover can extend this.
| Seepage
reduction |
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A pondage test on a 480 section conducted prior to lining, identified
seepage rates of 7.7L/m2/day at that site. While there has been
no post-remediation monitoring of seepage rates, clay lining is
expected to reduce seepage by 70-90%.
| Cost |
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The contract cost to clay-line 43,430m2 of the canal over a total
length of 2,140m was $640,000 at an average of $14.74/m2. Contract
rates varied for individual sections of the channel due to differences
in haulage distances from the borrow sites, producing a range of
lining costs from $14.25/m2 to $14.99/m2. Contract rates used assume
all clay material was imported from borrow sites. Due to the nature
of the lump sum contract, the actual costs for the alternative
method of mixing in-situ material before compaction are not available.
| Related
pages |
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Earthen lining
techniques
Compacted earthen liners
Clay lining example:
Channel 12
Other Australian examples
Channel bank lining
Loose earthen linings
Bentonite treatments
Modified soil earthen linings
Soil sealants |
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