[Geoff] Peter has a question here,
"In 13.32, Pond Walls, the short animation discusses
"where to best apply clay
"if it is in short supply.
"Would such a tamped clay cutoff work
"if the other earth involved is mostly sand?
"How low does the clay percentage of the salt need to be
"for you to consider using this method?
"How much of the wall does the core need to be?
"The whole width of the key?
"10% of the thickness of the wall?
"a 1/3 the thickness of the wall?"
Well, on this dam that was built in 2002,
the key was about as wide as this wall.
And it was,
it was deeper than the roof of a 27 ton bulldozer.
So, it was two and a half meters probably deep
at the base of this wall,
and we had enough clay.
But if you are short of clay,
you might move it over so most of the clay is on this side.
That side of the wall can be poor material.
And that could be quite sandy
and shaley, or rocky,
so the worse material goes on the outside
the better material comes in the core and the inside slope.
If you're really sure the material, you move the core
right over so the core of the wall,
going down to the cutoff, going down to the key weight
is mostly on this side.
And it's almost like a laminated wall
down that inside there.
And you really want to pack it down.
You'd like 30% clay in that material at least.
If you start getting less than that, possibly you should
think about incorporating a psyllium material like bentonite
because you could
it's cheaper to include it in the construction
and if you still have a problem,
then you might go ahead with bentonite and the material
and if you can fill the dam, you can then try one of these
new polymers that have been very successful.
And you don't have to re-earth work the dam construction,
the earth works doesn't need to be addressed
or reshaped if you're using a polymer.
But if you come in afterwards and you want a bentonite,
then you've got to strip off a foot of subsoil or top
usually subsoil underneath where the water line is,
put that to one side, lay out your bentonite so it's
all white right across the dam and put one foot of topsoil
back on, 300 millimeters, and compact that down.
And ideally fill it up then,
or if you can't wait for rain.
So it's not just a matter of putting bentonite in
if you really have trouble, you've got to actually
lay out the bentonite after stripping off 300 mil or
foot of topsoil and then put that back.
And that can't have any big rocks or stones in it.
So there is an advantage to using a polymer
because there's, you don't have to pay the extra
for the earth works.
But if you're in doubt as you're building
it's definitely cheaper to include the bentonite
in the initial construction phase because your earth
move is working there and can incorporate it in the,
in the construction process.
So, it's a matter of making a judgment call in construction
to pay that little bit more to get some bentonite
into the constructed compacted material if you think
you're deficient.
So here's some polymer,
one of these buckets will cover 10 meters by 20 meters
a surface area of a dam, like this one behind me.
And, it's like a crystal.
And it's a,
it's a crystal that when it hits the water,
it swells up like a snowflake and sinks to the bottom.
This material here
is called Seep,
the model that they produce called Seep,
which does a gradual seeping leak.
There's another product called Plug, where you've got
a much larger leak.
So, we're going to treat this dam here,
we've had it assessed, they don't think the leak is in
the tail end, they think it's in the deep end
near the dam wall, so we're going to go 20 meters by 10
with one bucket and 20 meters by 10 with another bucket.
Drop it in, draw down the polymer, and snag it all up.
This is Polymer Innovations, the company's called,
and that's
19 kilos there,
and it's been very successful.
People have reported that it works very well,
so we're going to give it a try, 'cause we've got a
good test case there with the dam behind me.
[Techno Beat]