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Soil-cement linings are constructed with
mixtures of sandy soil, cement and water, which harden to a concrete-like
material. The cement content should be from 2-8% of the soil by
volume. However, larger cement contents are used. For the construction
of soil-cement linings two methods are in general use: (1) the
dry-mix method and (2) the plastic mix method. For erosion protection
and additional strength in large channels, the layer of soil-cement
is sometimes covered with coarse soil.
It is recommended the soil-cement lining should be protected from
the weather for seven days by spreading approximately 50mm of soil,
straw or hessian bags over it and keeping the cover moistened to
allow proper curing. Water sprinkling should continue for 28 days
following installation (Sally, 1965).
Soil-cement linings are often a viable alternative to channel lining
if locally available materials are not suitable for compressed
earth or clay earthen lining. A great advantage of this technique
is that practically all types of soil normally encountered in earthen
channels can be used. For lining the beds of large channels this
type of lining is considered ideal from its combination of cost,
efficiency and adequate results.
| Dry-mix
soil-cement |
 |
The cement is distributed by hand-raking or by mechanical cement
spreaders to a uniform depth. While the cement is being mixed into
the soil with a rotary tiller, water is added simultaneously to
the mixture from a tank truck or hose. After the cement and soil
are thoroughly mixed and the moisture content determined to be
proper, the mixture is compacted by rubber-tyred road compactors
or heavily loaded trucks to approximately 100mm thickness, within
one hour of the cement being spread. The soil mixture is usually
cured for several days with intermittent sprinkling.
The durability and watertightness of the dry-mix soil-cement lining
depends on the soil used. Tests indicate that for ease of mixing,
placement and using a low cement content, the soil should be a
well-graded, sandy, gravelly material. If it is poorly graded then
the cement content required is higher and cost increases (USBR,
1976).
Material mixing for standard soil-cement is best accomplished by
travelling mixing machines or stationary plants. Mixing in place
in the channel and on side slopes has been found to be satisfactory
(USBR, 1976).
| Plastic
soil-cement |
|
Plastic soil-cement has higher water and cement content than dry-mix
and a consistency comparable to that of concrete used for slip-form
lining. The soil is mixed with cement and water in a paver or mixer
travelling along the channel or in a stationary plant. The mix
is then poured by hand or by slip form on the subgrade to produce
the lining. Thickness ranges from 75-150mm. It is recommended that
joints similar to those of concrete linings be provided.
Installations of soil-cement linings in the United States have
shown that the greater the cement content of the plastic mixture,
the more durable the liner. All of the linings installed continue
to be effective at reducing both seepage and erosion. The sections
with higher cement contents were made serviceable for many years
with reasonable maintenance (USBR, 1976).
| Related
pages |
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Hard
surface lining techniques
Concrete
Shotcrete
Grouted fabric mats
Flumes and pipes
Tiles and bricks
Asphalt |
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