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 is accurately mixed into a 100mm layer of soil, followed by wetting and compaction.
Mixed blanket usage rate:
|Course sand no fines
|Sand - 10% max fines
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 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.