Can I 'cast' wall foundations?

session savage

Hi all.
I have a small project on at the moment. I'm building a wall in my garden to split my sloping lawn into two levels. The higher level will slope down from a high point of 5 1/2 ft at one point on a circular wall, down to the same height as the lower level at the opposite point on the same wall.

This picture shows the two levels. The lower level was dug out and all of the earth removed was solid slig. You can just about see on the picture a circle showing where the foundations will be dug.



This shows roughly the shape of the wall I intend to build.


The purpose of the wall is to let me enjoy my view while protecting me from the wind if I decide to have a barbeque or outside session. When the wall is built I will need to fill in behind it to build up the higher level so the wall will need to be strong enough to support this force. (I'm hoping that the circular shape will help there)

Anyway, my question is....
I went out to dig foundations yesterday and the ground is basically rock. So I was wondering if I could just build a mould and cast my foundations on top of the lower level of rock and then fill in over them after.
Also will normal block be strong enough to support the weight of backfilling? Considering the circular shape I'm guessing it would be ok.
Heres what the ground looks like.



Anyway, I hope I explained it ok and thanks for any suggestions or help.

backboiler

You could consider getting a long drill bit (600 mm?) and putting a few holes per metre vertically into the rock so you can embed some rebar and then cast your concrete with these inside. That should stabilise it. Maybe bend the top end of the steel into a "7" shape for a bit more grip.
I wouldn't like to offer advice on the retaining wall but there are plenty of others here well able.

mickdw

I dont quite understand what you are saying about the foundations but in general, you would need to build that in 9" block. The circle should also be a help.
I would ensure that the foundation in dug into the rock to some degree to guarantee against the whole foundation slipping.
If dug in, with a 9" wall and some drainage material behind it, it would be 100%

session savage

Thanks lads.
What I mean about the foundations is instead of digging a standard faoundation (because I cant break through ground as it is rock) I was thinking of building a box the shape of the circle where the foundations are needed, so instead of pouring concrete into a trench as you normally would, I would pour concrete into a mould above ground.

Imagine this slab is the ground where I want the wall, this pic shows normal foundations




Now instead of that, could I make a mould like in this picture and pour the concrete into this?

mickdw

You sure can build the foundation in this way provided its on a suitable material and provided that it would not get in the way of the finished design. As I stated earlier, it would be of benefit to have it dug in as that would prevent any possible slip along the surface. Seeing as the ground is so solid, building it on top as you have suggested is the best option but I would still dig some deeper areas to give the foundation more of a key with the hard rock. If you dug maybe 3 small areas along the run of the wall, that would be pretty bulletproof even without that Im sure it would be fine.

session savage

Bang on Mick. I'll do that. Three or four holes should be do-able. I can raise the finished ground level after to cover the foundations so thats no bother.
Thanks folks.