DAM SEALING

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JNJ RESOURCES

DAM SEALING

Sodium bentonite is a naturally occurring clay material composed predominantly of the active constituent montmorillonite. On exposure to water, bentonite exhibits high swelling properties. Use is made of this in the sealing of porous soils where the swollen mass fills the voids and binds the soil particles to create an impermeable seal.

Sodium bentonite is best suited to in-corporation in coarse textured soils of clay content less than 10% because of the relatively easy workability. In high clay soils, incorporation is more difficult, both with respect to the placing of sodium bentonite, and to ensuing compaction.

The two most common application methods are:

MIXED BLANKET AND PURE BLANKET METHODS

As a general rule, the above usage rates are recommended for the MIXED BLANKET method where sodium bentonite (“Bent Blend”) is accurately mixed into a 100mm layer of soil, followed by wetting and compaction.

The mixed blanket should be covered with 100-150mm of compacted soil to protect the treated layer.

The pure blanket method applies to soils where accurate mixing of the sodium bentonite (“Bent Blend”) is not practical.

For the pure blanket method, the complete area should be covered at the rates indicated in the tabulation.

SEDIMENTARY METHOD

This method can be successfully employed for the repair of a leaking dam which is full or partly filled with water.

The principle involved is that when the granular grade sodium bentonite (“Bent Blend”) is sprinkled on the water surface, the product sinks to the bottom and is drawn into the leaking zones by the movement of the water. This method is only recommended where emptying the dam is impractical and the location of the leaking zones can be reasonably accurately assessed. Because this method involves no mixing and compaction, a minimum treatment of 25 kg per square metre is required.

MIXED BLANKET USAGE RATE

SOIL TYPE BENT BLEND

Coarse sand no fines.......................... 30 kg/m2

Sand with 10% max fines................. 20 kg/m2

Sandy loam......................................... 15 kg/m2

Clayey sand......................................... 10 kg/m2

MIXING RATES FOR DAM SEALING

Below is a table showing common names of soils against classification. This chart is in universal usage and will enable anyone constructing a dam to sensibly interpret laboratory results to a practical soil situation. Also included in the table is an indication of the quantity of “Bent Blend” which would be required to form a seal either using pure blanket, or mixed blanket methods.