Let’s Talk Dirty

The first thing we look at when inspecting a dam site is the dirt.

There are certain clay’s we look for, because they are the ones that create a permanent seal in your dam.

And there are certain clay’s we avoid

The dam walls have to be constructed with an appropriate and non-porous
clay material – otherwise the dam will lose significant water volume via transpiration through the dam wall

The clay that we avoid is called ultisol – more commonly known as red clay.
Red clay has less than 35% base saturation and no shrink–swell
properties. It known as a dispersive clay.

Red clay particles are able to move about
freely in water because they are not bound to other clay particles, or to
organic matter.

Red clay is inappropriate for dam wall construction as it will not retain
water, but rather let water drain straight through.

What we need to find on-site is a flocculate clay – and this clay is white in colour.

It’s the same clay used in pottery, and it becomes very sticky when water is added to it

Flocculate clays are the opposite of dispersive clays.

In white clay, the particles will bind readily to one another, creating a non-porous seal.

These clays are not prone to tunnelling.

If we can’t find a flocculate clay on-site, then we bring in Bentonite – which is the utlimate in flocculate clays.

Bentonite has a shrink–swell ratio of 1 to 400.

That means that each molecule of Bentonite swells to 400 times its
original mass when saturated with water.

During this process, Bentonite becomes a super coagulate – meaning
that when saturated, it holds the water and refuses to let go of it.

(coagulate – to gather together and cause to thicken into a coherent
permanent mass)

In effect, the water captured in the Bentonite stops other water
travelling through the wall – and more importantly, Bentonite becomes
more effective each and every day it is submerged.

There is no degradation in performance over time, and it will keep the dam sealed for up to 20 years

Read more about successfully sealing a dam