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Description
This type of lining typically consists of a loose, uncompacted
blanket of selected fine-grained clay soils dumped into the channel
and spread over the bottom and banks in layers up to about 300m
in thickness. Seepage can be reduced to an acceptable level economically,
provided available soils are sufficiently fine to have a low permeability
in a loose state and are adequately stabilised to resist erosion
to a reasonable degree by the provision of a cover layer of gravel
(USBR, 1998).
Although the serviceable life of loosely placed earthen linings
is relatively short (approximately 5 years was experienced in the
United States (USBR, 1976)), their use may be advantageous in certain
cases where low initial costs are essential. Costs are very low
because simple equipment can be used and little subgrade preparation
is required. Therefore loosely placed earthen linings have found
usage on both small and large jobs, but are generally expected
to reduce seepage for only a few seasons.
Some permanent seepage control may result from unprotected loose
earthen linings if the underlying soil contains voids into which
the fine-grained lining particles can penetrate and become entrapped.
On one project (Kraatz, 1977), consideration was given to placing
a 150mm blanket of loose plastic clay secured from a borrow over
pervious silty sand-gravel subgrade soils. It was found that the
seepage rate of the loose clay blanket was 300L/m2/day, while the
seepage rate from a 600mm compacted lining using the same local
material was only 75L/m2/day, 25% of that achieved with the loose
clay blanket.
| Related
pages |
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Earthen lining techniques
Compacted earthen liners
Clay
lining example: Channel 12
Clay
lining example: Waranga Western Channel
Other
Australian examples
Channel bank remodelling
Bentonite treatments
Modified soil earthen linings
Soil sealants |
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