Garage Pit

[j_mchattie]

I am moving to a new house soon, and it has a 4ft vehicle inspection pit. The walls are currently just stoney earth and I would like to shore it up a bit (a lot actually)

The pit is 2'6" by 7' and 4' deep.

Will I need rebar? Hopefully I wont because I cant get it in small quantities. I was going to just make a new plywood box all the way round the pit which is 6" smaller than the current hole.

Then I was going to fill behind it with concrete. Is that strong enough?

I will put a concrete floor in too, but my first job is to make the pit safer.

I will post the photos in a minute.

Thanks

 

[j_mchattie]

The photos are here

http://picasaweb.google.com/james.mchattie/Pit

Thanks

James

 

[Static]

If your looking to make it safe you should do it properly. Currently looks like someone has cut a hole in ground bearing concrete garage slab and dug out the earth leaving bare faced sides, then dropped in a few loose boards to stand on.

Properly means you form the walls and base from concrete(with rebar), and put in a little drain for wash down water and spilt petrol etc.

 

[j_mchattie]

Thanks for your advice - I is my primary aim to make it safe.

How thick does the concrete need to be? I am not happy about digging one of the sides out anymore than it is, because its only 3ft from the house. Obviously I will need to remove material to re-fill the gap with concrete, but I would rather make the pit narrower than dig any more out near the house.

Also, can you buy rebar in tiny amounts like that? I have tried to get some quotes from local companies but they arent interested.

Thanks

 

[Static]

150-200mm thk all round should do it judging from the photos, go for rebar meshes (ie A252 top and bottom) can buy that by the sheet and cut it up to suite.

Maybe consider if you need a pit, it may be worth filling it back in.

 

[j_mchattie]

No way! Its going to be ultra handy. Im doing an MSc in Automotive Engineering next year.

So 6" of concrete with rebar to boot. Would it simply be one layer of mesh (6mm?) all the way round?

And who supplies small quantities like that (I live in Gravesend, Kent)?

Thanks

 

[JohnD]

Try to cast a sort of ledge round the top so you can put timbers into it and they will lie flush with the garage floor.

 

[j_mchattie]

I will also try to cast a raised step all the way round to stop running water from entering.

This will be quite difficult for me as I havent done anything this large before, nor used rebar - so apologies for the rubbish questions!

Is rebar really required for a project this small? Bearing in mind the walls are holding as they are, even without the 6" of concrete.

 

[JohnD]

The problem is that the sides may push against the side of the walls, which have little strength. This can happen as the ground get damp or dry and expands or shrinks during the year; or as the soil slumps.

 

[j_mchattie]

It looks like the standard size for a rebar mesh (fabric) is 4.8 by 2.4m

I can get all the sides I need from one of those, including the floor.

You mentioned the 8mm rebar, but if its allowed I would prefer to use the 6 because if the weld spacing. Is one facing of 6mm rebar in 6" of concrete strong enough?

Thanks

 

[Static]

Your walls will be retaining 4ft of soil and a car.
Yes rebar is necassary.
A252 mesh is 8mm thick, i wouldnt go any smaller and yes a layer each side is also a must.
To keep it simple the mesh will also go in the top and bottom of the base slab.

The above will probably not be waterproof at 6"
I would still put in a small drain as water will find a way in.

 

[Nige F]

you can get fiberglass inspection pits from classic car mag advertisers

 

[j_mchattie]

STATIC - A layer each side.....

Sorry, what do you mean by this?

 

[Static]

150mm thick wall..
so section through looks like:-

40mm concrete cover
8mm (A252) mesh reinforcement
54mm concrete in middle
8mm (A252) mesh reinforcement
40mm concrete cover

 

[j_mchattie]

Ok,

Thanks all.

Ill let you know how it goes in a couple of weeks time.