Digging a trench.

[JackButler]

IF (& I don't recommend it) you feel the need to skimp on the footings, then you should really put a geo textile down first.

You don't know what you doing, do you?
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[Suntan Sid]

To set a level for the bottom of your trench.
You do not say what sort of level you have so I’ll assume it’s a laser, (it would be easier if you had a dumpy level and a proper measuring staff).

First of all you don’t need to be deadly accurate, +/- 25mm will be more than acceptable.

Mark out the centre line of the trench on the ground, some string and pegs will do.
Set stakes in the ground, just outside the width of the trench, at the corners and at intermediate points along the trench.
Site your level at a point where you can see all the stakes.
Centre the bubble on the level.
Using the laser, point it at each stake and mark the level of the laser on each stake.
Assuming you know how far below ground the footing must be, start digging your trench at the lowest corner and work from there.
As long as the bottom of the trench is an equal distance down from the datum marks you made it will be level enough!
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[MCN]

One word.

Theodolite.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Howling Terror]

One word.

Knackered.

People who aren't used to using a spade and shovel soon get knackered.
Most get blisters on inside of thumbs and across the palm.
Aching at base of back.

Do as doggone and Ste mentioned, oh and and keep your feet away from the mattock.

Spade and shovel I hear you ask?

Think of the spade as a knife and shovel as the spoon.
Shovel is kinder to the back too.
Combined they can be used in digging deep narrow holes.

Spent too long on the wrong end of spade n shovel.

Don't get me onto digging bars. When Andy hit the 11,000v cable and it blew off the end of a 2" diameter bar leaving Andy 10ft away on his arse...Impressive as he's a solid sort of fella.

Oh another word.

mini-digger.


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[Suntan Sid]

[Riejufixing]

So plane tabling's right out?

Dear God, I'm glad I did not ask how to build a molehill, only how to get a level flat bottom in a trench.

I'll knock some pegs in and use a spirit level, sort of like your suggestion above.

[Howling Terror]

This is BCF, we aim to get at least 3 pages out of this quandary you find yourself in.
____________________
Diabolical homemade music Bandcamp and Soundcloud
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The Harry Turner Project

[MCN]

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[Ste]

It wants to be vaguely roughly level so that you're not digging out more than necessary and so you don't need to mix an excessive amount of concrete but other than that, you just start digging.

[MCN]

[Chuffin Nora]

[Pete.]

[Islander]

Have you thought about what you're going to do with the spoil? By the time it's out and broken up, you'll end up with about 1.5 times the volume of the actual excavation...

It was the single biggest problem I had when I put land drains in here and I've got a 1 acre field and the shoreline for disposal.

Oh and hire a mini digger. They're dead easy to drive, are great fun and you can get a lot done in a fairly short space of time. Do it by hand and it'll take you a lot longer than you think and you'll suffer.

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[Ste]

[Pete.]

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At the end of the day, OP needs to stop fannying about fretting about making his hole pointlessly flat bottomed, and needs to accept the advice that he won’t be doing this by hand.

Nobody yet has managed to explain why the fecking trench needs a perfectly level bottom surface, when the liquid concrete will level out at the top surface anyway.

I’m stumped with it.
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[Diggs]

Lots of nonsense here. If the building is to be 5x6m it is unlikely to need deep strip foundations and (presumably) a suspended floor. Most likely it will have a concrete floor which will be formed by a slab on compacted hardcore. OP will need to dig out to 400mm minimum to allow for 250mm plus 150mm concrete. Roughly speaking this will need two skips, and filling two skips by hand will kill the OP so I predict him hiring a man with a Bobcat sharpish... O.P. will have to import 10 cu.m of hardcore which will also kill him. Unless he can pump his concrete he will need to carry and mix 5 cu.m on site, which if he is still alive by that point will finish him off for good... Methinks the O.P. does not understand what is involved 🤔
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[Diggs]