Concrete garage base and tree root problem. - Tree roots from removed tree under area.

[MRRB]

Quite a while since I looked here, very different now, well done over the years!

Anyway, the description, I'll put in the whole plan, warts 'n' all. I want to repurpose a concrete garage, which I got free, in my garden, for storage and DIY. The base size will be just 6m by 5m. I will be doing all the work by hand, incidentally, since I am currently very poor indeed. It won't be a civil engineering job. I want to do the best I can by hand with very limited resources.

The topsoil is sandy, free and well-draining, the subsoil is hard ochre-coloured stuff with numerous inclusions of sandstone shards, like large pieces of broken scotch egg "meat".

I have already removed (last July) a conifer tree from where one corner of the base will go. It was about 45' high, and 2' thick where I cut it, and was a lot of work. I dug out the stump, too, which was a lot of work, leaving a hole about 8' square. The tree was growing slap bang on the rear-right corner of this new base.

The problem is that under part of where the base will go, there are still roots. They probably extend a fair way under the area. Where cut, one is about 4" thick, one 3", and two 2". Luckily, most went the other way. The thick one looks as though it runs along one edge of the area.

I can dig out some of the thick parts of the remaining roots, then ram the soil back in with a rammer. I don't want to dig the whole area if at all possible, because a) huge effort, plus b) it will disturb the ground which I will then have to tamp down and might not "match" the rest.

On the base area, I intend to concrete a strip around the edge 8" deep, mixed with a minimix-type mixer, incorporating reinforcing mesh, and infill in the rest to 100mm in areas as possible, using a joggle joint type of join.

It is likely to be a bit wibbly-wobbly anyway, but it's the roots that are concerning me most right now.

Anyway, confession made, can anyone suggest what would be best, given the circumstances, for the roots?

[Tony McC]

It's a bit difficult to envisage all this but, assuming I have the right sort of image in my mind.....

Remove as many roots as possible.

Fill any voids with fine gravel, coarse sand or even a slurry mortar rather than "ramming-in" earth.

Min 100mm sub-base for concrete base.

At 6m x 5m, you'd need 200mm concrete thickness throughout for structural integrity, or split it into 4 small slabs @ 3m x 2.5m and fix with ties/dowels.

[MRRB]

Thanks for the reply. I'll do what I can with the roots, the thicker parts anyway. I can't excavate further for a sub-base unfortunately, because of the various costs (I am not kidding about the money, and it's got to be done starting now) so it'll have go on the earth (DPC I assume for curing?), so it's not going to have a lot of structural integrity, although I do hope it holds together at least somewhat. Bloomin' 'eck.

[MRRB]

Well, I've dug out a lot of roots. That was a lot of work.

Basically it'll be a ~5m x 6m concrete slab with what was the tree having been removed from the back RH corner (the trunk was on the spot where the BRH corner will be).

Questions.

Why not pack earth in with a rammer? Because the density of the soil may be greater or different from the undug areas then heave or subside (?)

I think it's going to be 6-8" deep (?) around the edges, 4" in the middle. Unsure about the deeper margins' width. 600mm (?) with 6mm (?) reinforcing mesh to hopefully keep it together somewhat. Not sure if mesh all over would be useful oor a liability. Any comment?

It'll move, I'm sure. Hopefully the fact it'll be a lot of smallish areas jointed will give a "flexible paving" effect and not result in a major crack/step.The question is how much, and I have no idea. I hope not as much as 25mm! The concrete building itself will be a little flexible, as will a tin roof over flakeboard.

So if ASCII art works, one edge will look like, in elevation/section:

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| <- prefab wall
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|======================================= internal flakeboard
####600mm###/#####950####/#####950#### top slab
#---------------------\-----------------------\----------------------- mesh encased in slab
# ##/############/########### bottom slab
########## ^joint ^ joint
150 or 200 deep 100 deep 100 deep

Strip of slab all around edge thicker 150 mm or 200 mm, middle 100mm.

What will happen?

[Tony McC]

Earth *never* compacts as predictably as crushed aggregate. Why risk it?

100mm is not thick enough for a slab spanning 5m or 6m, regardless of how deep you make the toe at the edges.

[MRRB]

I haven't any money. Had I any money, I would hire skips in, hire a mini-digger, take off the top foot, put down aggregate, compact it, and get a delivery pumped in. Come to that, if I had money, someone else would do the job!

But I haven't got any money! That is the whole problem! I've enough - just - for concrete, if I mix it. I've enough, just, for a tin roof. The bit in between already I've got. I need something urgently, it can't wait, else it would, so I am trying to do what I can.

Thanks for the info about compacting soil, I suspected that. The stuff's sandy. When it dries it goes dusty, and birds like to bathe in it.

Edit: Sorry, I am not trying to be rude in any way.