'Deep' patio needs a lot of hardcore/sub-base...

boxa

Hi everyone, I would be really grateful of some help re a patio I am about to build. I like to think I am a fairly competent DIY’er and have done a block paving and patio before with good results, but this is a bit of a bigger project.
In short, the patio itself is going to be ‘pie slice’ shaped and my main concern/how to question is the hardcore/sub base I need to use in the deep section against the retaining wall (the depth here is approximately 1.2 metres). As you can see by the photo’s I have attached, I have bit of hardcore I can use as sub base, which I was going to break up into approximately half house brick size and smaller (although I appreciate I am going to need a lot more) but from there do I kind of put layers of hard core down interspersed with compacted MOT 1? Or do I do something else?
Also, the retaining wall itself is double skinned (if that is the correct term to use) and I am also thinking about what I should feel the gap between the two retaining walls sand/cement/concrete mix???
Thanks in advance,
Paul

Doozergirl

The entire height of that wall is going to be retaining?  

It doesn't look very 'retainy' 😬. 

What reinforcement does it have?  The skins don't appear to be tied together, even. 

Martin_the_Unjust

I’m with Doozergirl on this, I’m pretty sure your retaining wall isn’t.

boxa

OK, sounds like a cop out but can assure you it's not...
I didn't do the wall but there are not ties in it. My understanding is the plan was to place some kind of sand/cement/concrete mix in-between.
So obviously going back a step from my original question then, what are your thoughts now on the 'retaining' wall and if you feel it is not a 'retaining wall' how I best correct it.
Thanks for the prompt replies.

Martin_the_Unjust

Fill it with concrete would help but I’d be putting some filled gabions behind it.

daveyjp

The usual way is to pour the concrete in shutters and then face it with blocks.

Pour concrete in between now and you risk a collapse.

boxa

Righty, so not sounding great at this stage then 
Ideally, do not really want to go down the gabion route, any other potential options/solutions?
Cheers.

Doozergirl

I think gabions would be a relatively cheap option. 

I'm afraid that I wouldn't use that wall at as a retainer at all.  

Dig the patio down?! 

boxa

Apologies, when you said about the filled gabions behind, do you mean placing them 'within' the patio area and before we get to the first skin of the wall? if this is the case it's an option. My initial thoughts were you meant the other side of the wall.
Thanks (and apologies for any stupid questions 

stuart45

You can retro fit ties, it would be better to tie the skins together. You can also fill the cavity with a lean mix, it's a standard thing to do with the cavity up 225mm below DPC. one of the main problems with retaining walls is water pressure, so if the area under the slabs is kept dry it stands more chance.
The depth of the fill could cause settlement problems, anything over 600mm on site and a suspended floor would be used.
Might be worth using brickwork on top, and running the slabs to it like this.

Martin_the_Unjust

boxa said:

Apologies, when you said about the filled gabions behind, do you mean placing them 'within' the patio area and before we get to the first skin of the wall? if this is the case it's an option. My initial thoughts were you meant the other side of the wall.
Thanks (and apologies for any stupid questions 

I meant within the patio area.

Basically build a stronger gabion wall behind the current walls up to a height where you can lay your patio almost directly on top of the gabion wall. If that makes sense?