G'day welcome back to Buildsum and in today's video what I want to talk about is
Excavations and how we make them safe for us to enter them so here in Australia the deepest trench
that we can get into to do any work is
1.5m deep and on the average person is about 1.8m tall it comes up to about there
Now one of the reasons for that is there's a thing called
Compressive Asphyxiation where if you get too much weight on your chest you can basically suffocate, so if you were to get a Trench collapse
Then with the 1.5m depth you're not going to get too much material up around your chest
And this all course assumes that you're standing up at the time that the Trench
Collapses, but anyway, that's the depth 1.5m. So what happens if
you are required to get into a trench. that's a deeper than 1.5m. What can we do, well
There's a couple of different methods. We can use the first one is called Benching and
basically what it is is stepping the Trench in
maximum 1.5m steps
And making sure that this side is back far enough that if it was to collapse
It wouldn't subsequently fall into the trench. It would stay on this step. So that's called
Benching or some people stepping but it's commonly known as
Benching part of this as you can see a lot of excavation required a lot of material needs to be removed
just to get a fairly small Trench, so
Not very commonly used
The other method is called Battering
again a lot of excavation' this angle that this is cut at should be the angle of repose and
I have another video explaining what that means
but
again lots of excavation so not not too commonly used and
Of course there's a combination of the two, so we've got a bench here
and then in a batter on the side again angle of repose, so
Not a lot of over excavation but still
Still a lot of escalation for a fairly small Trench, but these are possible methods
Okay, if you've got all the time in the world to dig the hole then no problems
The other way we can do it is we can use some Shoring
Systems and the most common you may see on big road work sites are shoring boxes
so these are just
preformed
boxes that have jacks basically in between them they get dropped into the trench with a
Excavator and you can jack them apart or pin them apart so that they hold the side of the trench up
And you've got a couple of choices you can either
Drag them along the trench as you need them so you're always working in between
the
Shoring box or of course you could put a whole heap in but depending on your costs
You may not want to hire heap you may just want to have the one
The other method or a nother method these are not the only methods
But as with a call sheet piling and particularly in very unstable soil
this is a common method where the
Shoring is put in first and then the excavation is done later, so it's they use
sheets in normally six and nine hundred millimetres wide fairly thick steel and up to a couple of millimetres thick and
these are clipped together
to form Walls
to form the Trench and then then actually driven into the ground on
Both sides driven all the way in and then you can excavate
in between the two sides
Obviously, they're driven further into the ground then the actual depth of the trench so that they're holding here and then
Once they're dug you need to put some
extra
support in the top to stop the top pushing over but once that's done then obviously you can to get into the Trench and
Work fairly safely there without the Trench caving in on you
alright, so there's the
three methods of working safe in a Trench Benching
Battering and a combination of those and
Shoring and as I said there's heaps of different methods of shoring
And the ones I've shown you just a couple of common methods that I'm aware of