How to build a foundation for a 20ft / 6m container?

[Sopwith]

Hi there. 

I'm a long time lurker on this site and have found so many excellent pieces of advice. Thank you all. An incredible resource.

But now I'm in need of something more specific. By way of background:

I inherited a bush block in S Tassie with a cleared area (7m x 18m),where one par,t 7m x 8m been taken back to clay. It is fairly level. At the back of this level site is a ditch about 500mm wide and 500 deep that runs the 18m that the previous owner was going to turn into a French drain. The reason is that beside the open area where I want to put the container is an old steel shed on a pretty bad concrete slab. The run off from the hill behind was entering the shed. I intend to use the shed to put larger things in (e.g. car).

I want to put a container on the site to store tools and so on and use as a shelter. Ultimately, say in five or so years, the container would be removed (and likely the shed too).

My question: What base should I put the container on? Advice has ranged from:

just put it on the clay;

plonk it on a couple of sleepers;

use some concrete blocks

pour a slab;

I would prefer to use as little concrete as possible, but would use the DEKO blocks. My concern is the clay. 

I'm thinking of a boxed base, with compacted crushed coarse stone, rather than road base.  Perhaps I'm over thinking it or on the wrong foot entirely.

I would be very grateful for any advice and suggestions. I can get access to a compactor and have all the usual tools. 

I should add, there is no power to the block at the moment, though I do have a generator. 

In advance, thanks.

[JacobZ]

Hi @Sopwith,

Thank you for your question and welcome to the Bunnings Workshop community, it is fabulous to have you with us.

Is it possible to get some photos of the space? This would certainly help our members determine the best way to go about installing a foundation for the container. Let me know if you need any assistance with this, I'm happy to help.

As clay is a very compact material, it might be worth getting some soil testing done. If the soil tests come back saying it is suitably compacted to support a load, you may just need to level an area, use some timber sleepers as dunnage to raise the container slightly and plonk it on top. As you've suggested the container would be removed in the future, this might be the cheapest way of doing things before installing something more long-term.

If this isn't possible, the first thought I had is exactly what you were thinking. A timber box, slightly larger than the container, made from sleepers that are connected together and anchored with retaining posts. It can then be filled with a material such as drainage gravel or road base, compacted and levelled to support the container.

This would still be a fair bit of work, but it would certainly be cheaper and easier than pouring a concrete pad.

Allow me to tag some of our helpful members to see if they have any other ideas, @JoeAzza, @Nailbag, @Jewelleryrescue, @Noyade.

Let me know if you have any other questions.

Jacob

[Sopwith]

Hello JacobZ

Thank you for your reply, which is helpful indeed. I'm going out to the block later this week and will snap photos then. 

I have soil tests for another part of the block where I hope to build a small cottage, but not this particular part as this was only ever considered temporary. I understand geology can change over a short distance. 

The site where I was thinking of placing the container was excavated out of a slope and I'm having that assessed which is not a small cost. 

In view of the mounting costs before I move on to the main game, I'm now rethinking my approach. 

[EricL]

Hello @Sopwith 

It's best to do the soil testing with safety in mind. Should your plans change in the future, you'll know that leaving the container in its current position would be safe. The last thing you want to happen is to have your container leaning over to one side due to soil settling.

We look forward to seeing the photos.

Eric

[Sopwith]

Hello EricL

Thank you for your advice, which is very reassuring.

As you will see from the photo below, the site is swampy. I am going to get soil testing done as well as some professional advice on how to keep the area dry, should it be suitable for a container. 

I am actually discovering more and more about the block, and an old steel shed there and will have some queries on that (but under a different topic).  I'm just at the gathering information stage.

Thanks again for the comments and advice.

[EricL]

Hi @Sopwith 

Thanks for sharing that extra photo of your proposed tool site. Is there any chance that you have an alternative location? I only worry that due to the pooling water it could be an indication of heavy clay content in that area. 

Please keep us updated with your progress, we look forward to seeing your shed being built.

Eric

[Sopwith]

Hello EricL

Thank you for your reply.

You are quite right: the site there in the picture is more or less clay - and although I will get a advice, I do not think I will plan on using it.

I do have another location, further up the hill. It still has the top soil intact. But, I'll put getting a container on ice for a while until I can sort out a suitable site. 

As regards the shed. It is a 35 year old steel shed, 30m2, and is dry and sits on a 75-90mm slab (depending where it is measured). The slab is generating a fine, talcum powder like grey dust. The shed is located behind where I was standing when I took the photo of the clay area. 

I don't know if it is possible to coat the concrete slab to reduce the generation of the dust. Using the shed as storage, instead of a garage, is certainly an option.

Grateful for any views.

If I could stabilise the slab so it does not generate dust, that would be a cheaper option. I would look at lining it in some way. 

Thanks for your message and reading and any comments you may make.

[EricL]

Hello @Sopwith 

When you get a dusty surface on a concrete slab, it is an indication of two things. First, water could have been applied to the surface while it was being finished. Second, the concrete mix was too wet and was not addressed while curing. In either case the surface has to be professionally resurfaced. 

I propose engaging the services of a concrete slab specialist. They will be able to resurface the slab safely and correctly, this means that it will be up to code and will not be prone to cracking under stress. 

If you have any other questions we can help with, please let us know.

Eric

[Sopwith]

Thank you for your reply, EricL, which is appreciated.  I had come to think along the same lines. The shed and the associated muddy area in the photo are on a bush block. I'm still trying to find out the state of the site and the shed. I definitely need to get some expert advice.

Regards

S

[Sopwith]

Hello

As I've posted I'm trying to work out what I might do on a block I have, and on the block is a 30+year old shed. The shed has  an insulation ?blanket? or ?sarking? - not sure. Is it possible to identify it from these pictures? This blanket has been installed in only some of the shed and it is next to the outer cladding. 

Grateful for any informaiton.

S