Retaining wall advice

[PeteWilliams]

Hi,

I'm looking to build a garden office at the bottom of my garden on what used to be a vegetable patch. As such, I was looking to lay a concrete slab as a base. Where my build differs to those I've seen elsewhere is that the area I want to build on has a drainage ditch directly next to it.

See photo of site: https://imgur.com/XQFtg9X

And a rough drawing of what I want to end up with: https://imgur.com/S9MECCa

Currently the soil is retained by some concrete slabs embedded vertically and some wood as you can see in the photo. I'm assuming that to support the weight of a base and building I'd need some form of retaining wall? It'd be a timber-framed building approx 4 x 5m.

I'm a DIYer so don't have any experience of this and am wondering what's the best way to approach this (or whether I need to get a pro in). Build a brick/breezeblock wall? Create an L-shaped former for my base so the a concrete wall is built too?

Any suggestions?

Cheers

Pete

 

[jasonzyx]

As no-one has offered any advice so far, I'll offer mine, although I am no expert on such matters.
You have, I think, quite a problem there.
A simple slab is prone to under washing (I don't know the technical term for it). Basically any water flow in the ditch could undermine the slab, even if it is only for a timber shed. This undermining could cause the slab to crack, break or shift.

So I guess the better solution is to provide an impermeable wall to your side of the ditch. But that means taking a foundation well below the bottom of the ditch, and of course, you are limited to your own property, which could pretty well be pointless, unless you included returns to the ends. A squared off 'U' shape wall, like this |_|, with the bottom of the 'U' acting as one side of the ditch.

So the cheaper alternative is to have a slab suitably reinforced, and anchored to resist breaking, cracking or shifting. My suggestion would be a reinforced 100mm thick slab with some short in-built piles connected to the slab via the reinforcing.

 

[conny]

I'm no expert either but my thoughts are trying to lay a drainage pipe or channel to take any water past your site to prevent 'under washing'?
Obviuosly you would need to extend it past your site for a distance safe enough to prevent any water going around the outside of the pipe.

 

[Dereekoo]

You could always forget about doing anything to the ditch wall and reinforce your concrete slab towards the ditch end so it cantilevers over the area of ground adjacent the ditch.

 

[akist]

You are building on the banks of a river, this is easy, has been done millions of times before, large cities, the Thames, Venice even? There must be a standard technique. Looking at man made harbours, reveals the use of rocks, sometimes gigantic, to form the wave breaker, water barrier and substrate, and a concrete pour over the top to create the platform on which to build (or walk). Sometimes instead of rocks (the size of cars) they use concrete columns like scattered, gigantic bowling pins. That's how Jeremy Clarkson would approach it. I imagine Richard and James looking on in disbelief as huge lorries arrive to deliver 10 ton rocks.

Maybe I'd build a U shape, concrete, underground dam and foundation, as has been suggested above, and i'd pour a concrete slab over it, with some iron bars to tie them together.

 

[Dereekoo]

You are building on the banks of a river, this is easy, has been done millions of times before, large cities, the Thames, Venice even? There must be a standard technique. Looking at man made harbours, reveals the use of rocks, sometimes gigantic, to form the wave breaker, water barrier and substrate, and a concrete pour over the top to create the platform on which to build (or walk). Sometimes instead of rocks (the size of cars) they use concrete columns like scattered, gigantic bowling pins. That's how Jeremy Clarkson would approach it. I imagine Richard and James looking on in disbelief as huge lorries arrive to deliver 10 ton rocks.

Maybe I'd build a U shape, concrete, underground dam and foundation, as has been suggested above, and i'd pour a concrete slab over it, with some iron bars to tie them together.

Looking at previous Akist post re slab spec for small outbuilding I have concluded that he is a lonely sole looking to somehow interact with other people. Unfortunately he has chosen this forum as his way of doing that, best ignore him and he will no doubt go away