G'day and welcome back to Buildsum and in this video
what I want to talk about is grade or how we can calculate and how
The slope of the ground is expressed as you can see here
And as you'd realize not many building blocks are actually in level or flat. They normally have some sort of slope and
Quite often we actually might have to build in a slope
onto our block whether it's just a drain off surface water or whether are actually digging a trench which is gonna have a
Pipe in it and that pipe needs to fall for sewer or
stormwater type reasons we're gonna get told
what angle or what grade our
natural or our prepaired ground needs to be at
so
There's three ways that that angle is normally given to us
Okay, and the first one says a ratio
So in this case, we've got a ratio 1:10. So basically that means
In this case, I'm gonna work in meters for every 10 meteres
That the ground runs then it actually rises one metre
Okay. See you could have a ratio of 1 in 20, 1 and 15 depending on
The slope that you're actually required so it's gonna be 1:10. That's the first place. That's a ratio
So I'd actually work out how far the ground rises for every metre
All you need to do is divide the 1 by the 10 or the rise
by the run
And that would give you an answer of
0.1 or 100 mil so for every metre
that
The ground comes across or that you come across you're going to go the wrong with ground is gonna rise
100mm
so therefore if your times the
0.1 by whatever length you happen to need you're gonna get the actual rise at that point
so become 2 metres in that's gonna rise 200mm and if you come three metres in it's going to rise 300mm and
So on. Okay, so the the
Calculation you have to do is just divide the rise by the runvto
Give you this little factor and then your time's that by the length that you need
That'll give you the actual rise of the ground at that point
Okay, so that's ratio. That's the first
Method the second method is it like roofing they just give you an angle
Okay. So in this case I've picked 5.7 degrees, you'll see why in a minute
So the angle is this angle down here
Okay, the the smaller of the angles in the actual triangle so 5.7 degrees so to actually get the rise of that
If you do TAN
times the run so TAN angle will give you
The rise per metre so if you did TAN
5.7106
you'll get 0.1 one same as we did for our ratio and if you then times up by the
Distance that you need here then in this case 10, you'll get a metre so it'll give you the rise
Okay, so we can get it given to us as an angle and
We can also work backwards and work out what our angle is, if we get given a ratio
for example and
we want to look at what the actual angle is what we can do and
Yeah, we do our rise divided by run and then in our calculator we use the inverse TAN function
Which means gonna have to hit the shift button in most cases and then the TAN button
There remembering if you do if you're using a slight scientific calculator on your phone
the order of operation could be slightly different you might have to do shift TAN and then do the
rise divided up a run to get the answer to come out right, but that's the process
So in this case, it would be 1 metre
Divided by 10 which we know gives us 0.1
Shift TAN or inverse TAN it'll give you the actual angle of that slope so 5.106
degrees in this case
Okay, so that's angle that's 2 so we have got ratio, got angle and the last one we can get is a percentage
Okay, in this case 10% and all the best thing to do with a percentage is just to convert that back into
a ratio so
10%
Means that this particular to the land is going to rise
10 meteres for every 100 metres of run
okay, and if you divide
10 into 100 obviously you're gonna get 1 and
10 so we are back to our 1:10 ratio
okay, and
Again the way we can do that if you
So if you take the 10 and it's a
Stumbling so take the hundred and
Times that by 10% you get a rise 10 metres which we did. Yeah
All right, and it's same if you had a run of 10 meters
And it times that by 10 percent you're gonna get a rise of 1 meter which we know works this bottom end
Okay, so there's the three different ways
They grade can be expressed
on our plans and as I said we can use it to
grade the block of land to drain water
Or maybe we've got a dig trench and put a pipe in for sewage or or storm water or something like that
and we can actually work out how far the
The ground has to rise or fall for the distance that it travels
G'day I'm back
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