G'day and welcome back to Buildsum and in this video, I'm gonna start looking at what we call a long section, so
The main reason we would take a long section is if we're gonna work out
Say I'm gonna dig a pipeline or a trench and we want to work out how much
material we need to excavate then we do a long section and the long sections, basically
We do a straight line survey of an area and then from that from our readings we can calculate and plot
The actual shape to the ground and then we can work out our excavation. Okay, so
Here's our block of land and and here is the trench that we want to dig
It's about 50m long and obviously the grounds not level
So the grounds up and down and our trench has a bit of a slope to it
Because we're gonna put up sewage pipe or storm water pipe in here, it needs to have a bit of fall
Okay
So to do our long section, the first thing we need to do is what we call straight line survey
So we need actually break this
Trench if you like up into an even even points
And the closer together those points the more accurate your long sections gonna be at the end
Okay, so I've just gone with 5m
I mean you could go 10m depending on the overall length of the trench and
The overall detail that you want to have on your long section
Yeah, but 5m a pretty good so I've identified from the start of where the trench starts to the end
I've broken that up into
reasonably, you know even
Points and that's where we're gonna take out readings if your trench was
52m long
it's not really gonna matter as long as the majority of your readings are evenly spaced and then you just have
Whatever the like diaries at the end you can you can work with that
Okay, so I've identified or spaced out my readings obviously. I've got to identify
What my readings are gonna be so, you know point one through the 11 in this case or you could have A B and C
And the other thing we need to do to do a long section is we need to know a height
Okay, so there's our readings we obviously when we do our survey for a long section
We've got to get back to and datum of some sort
Benchmark or a datum on their job site. All right, so we're gonna do a out survey a straight-line survey
To our datum starting with our datum and then all our points along our trench
You don't have to close the survey
Although it's good if you can just as a check
but just take a reading of all those points and then we're gonna put that in the level book and
Create a long section from that. Okay, so we've been out on site and we've done our
Readings and we can then put them into our level book doesn't matter whether it's rise and fall or height of collimation
But we need to produce an RL for each of the readings that we took so we had eleven readings
I've now got eleven RL's
You'll need to make up a bit of a graph
Looks something like this as a table at the bottom and just some graph lines across the top
I'll show you what they're for in a sec
But the first thing we're going to record is what we call the surface RL
So that's basically the RL of the reading or the points that we've taken off our level book
So these are RL's here
The RL for point one is 30.212, it just goes into
That column here in the surface RL row and we just go along and we put all those our RLs
straight in
To our graph so we have an RL for each of the points of our
of our
Long long section, okay
So once we've done that we can get rid of our level book. We don't need that anymore and then we're gonna actually plot
where these go on our graph up here, so
What I've done is I've said that this is going to be 28
I've had a little bit of a look at my readings
I don't know that we're not gonna have anything less than an RL of 28, even when we put our trench in here
so I'm gonna set this baseline at 28 because just below that is nothing so we're not going to need it and
We can scale this up
Or in this case. I've just broken my graph up into
Some equal sections. So I'm going to say that this is 29 has an RL 29 on this line
This line here has an RL of 30
You can keep going if you want. Does that need to I'm not going to be much over 30
But the other option is you can just scale these up with a scale ruler if you need to
Okay
So what I'm gonna do, I've got my RL here of 30.212
And my base line is 28. So the difference between that is
2.212, so if I had asked our ruler I would just scale
2.212m
up this line t00 and you'll just have to pick a scale which fits on your on your page
Okay, so but I've said here that I'm gonna go 30.212, so I'm gonna be up around
Here somewhere. So I'm just gonna put a mark on my graph to represent that so
This one here is30.378
So that's gonna be slightly higher
then this mark
so I'm gonna put a line there and
30.429 again. It's gonna be slightly higher than this one. And then this one's exactly the same as that one
So I'm just going to come down to the same level
This one's coming down so 30.125 is gonna just above this line here and
Then we're gonna in 29.387, so I'm going to be below the line
Okay, so I'm actually just trying to create a representation or where those points are on the ground
You can see I'm starting to get a bit of a representation of the shape of the ground
As I said these could be scaled up or you can just plot them break up to graphically and plot them
We're just looking for a look at the ground. I mean, it's not going to be a great representation
because obviously the scale
Going this way. It's not going to be the same as the scale going this way
Only talking this is 50 meters long this way and we're only 2m high that way so the scale is never going to work
so
the next one, 29
It's a little bit lower this one .29.5 So we're halfway down that line. This is below half
They're a little bit below the halfway point on that line
They're 29.6 we're going up again
29.9 we're going to be virtually touching in that line and
29.8 1 it's just a little bit lower than that. Okay
So I've plotted all those points and then I can
Join them together. You can't do straight lines, but you know straight lines aren't natural
so just do a nice freehand curve and that will give you a
representation of
The slope of the ground remembering that shape of the trench from the start
It did start up higher than start and then it went down through a dip and it came up at the end
so we have just the
representation of what the ground actually looks like
So that's plotting the long section
And getting of the representation of the Earth's surface or the natural surface natural are RLs in the next video
we'll go through actually plotting a trench and
And actually getting to see and work out the depths of the trench at each of these points
G'day, I'm back
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