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

weeg

A good rule of thumb for mass gravity retaining walls is that they want to be about 3/5 width to height ratio, so at 1.2m retention, i'd be looking at 600-700mm width at the base, narrowing as it came up. 

I've you filled that gap with a sand/cement mortar mix it wouldn't do any harm, but equally it wouldn't actually function as one wall.

So your option are either widen that block wall, or put something in to stop the wall taking the weight. (Hence the gabions suggestion above). We use dense polystyrene a lot, but it's not cheap.

boxa

Martin_the_Unjust said:

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?

Thanks MtU for the explanation. If the gabions went down within the patio area, would I then have to create a subbase from the top of the gabions e.g. MOT 1, whacking/compacting it down as I go and then the bedding layer on top of that?
Also, as you can see there are steps going down to the 'retaining' wall. Could I put bricks/hard core down to approximately level the part bottom step with the one above, then place gabions on top of this now elongated step?
Also, nearer to the top of the steps there is obviously not as much depth, could I therefore then put some hardcore there against the gabions already placed down?
One last question, what would I put between the gabions and the 'retaingin' wall, as there will be a gap where the wall is curved?
Bl00dy hell, gonna be a toughy this one! I know I can do it, but I am a bit of a thinker, the other half says procrastinator , so will definitely have to get my head around things before going forward.
Thanks once again MtU and everyone else for their advice so far. I'm taking it all onboard.
At the moment I am thinking gabions are going to be the best way then, but open to other advice...

weeg

boxa said:

Martin_the_Unjust said:

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?

Thanks MtU for the explanation. If the gabions went down within the patio area, would I then have to create a subbase from the top of the gabions e.g. MOT 1, whacking/compacting it down as I go and then the bedding layer on top of that?
Also, as you can see there are steps going down to the 'retaining' wall. Could I put bricks/hard core down to approximately level the part bottom step with the one above, then place gabions on top of this now elongated step?
Also, nearer to the top of the steps there is obviously not as much depth, could I therefore then put some hardcore there against the gabions already placed down?
One last question, what would I put between the gabions and the 'retaingin' wall, as there will be a gap where the wall is curved?
Bl00dy hell, gonna be a toughy this one! I know I can do it, but I am a bit of a thinker, the other half says procrastinator , so will definitely have to get my head around things before going forward.
Thanks once again MtU and everyone else for their advice so far. I'm taking it all onboard.
At the moment I am thinking gabions are going to be the best way then, but open to other advice...

 You'd put terram/ geotextile down over the gabions, then the bedding layer, which would stop the sand disappearing into the gaps.

Yes, you could level off the bottom step with hardcore before putting the lowest gabion.

You could put hardcore between the gabions and the wall, again if you put some sheeting at the side of the gabion to stop it falling in.

You sure it isn't easier to just build more wall?

boxa

weeg said:

boxa said:

Martin_the_Unjust said:

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?

Thanks MtU for the explanation. If the gabions went down within the patio area, would I then have to create a subbase from the top of the gabions e.g. MOT 1, whacking/compacting it down as I go and then the bedding layer on top of that?
Also, as you can see there are steps going down to the 'retaining' wall. Could I put bricks/hard core down to approximately level the part bottom step with the one above, then place gabions on top of this now elongated step?
Also, nearer to the top of the steps there is obviously not as much depth, could I therefore then put some hardcore there against the gabions already placed down?
One last question, what would I put between the gabions and the 'retaingin' wall, as there will be a gap where the wall is curved?
Bl00dy hell, gonna be a toughy this one! I know I can do it, but I am a bit of a thinker, the other half says procrastinator , so will definitely have to get my head around things before going forward.
Thanks once again MtU and everyone else for their advice so far. I'm taking it all onboard.
At the moment I am thinking gabions are going to be the best way then, but open to other advice...

 You'd put terram/ geotextile down over the gabions, then the bedding layer, which would stop the sand disappearing into the gaps.

Yes, you could level off the bottom step with hardcore before putting the lowest gabion.

You could put hardcore between the gabions and the wall, again if you put some sheeting at the side of the gabion to stop it falling in.

You sure it isn't easier to just build more wall?

Thanks weeg, but stupid question time again I'm afraid...
When you say build more wall are you saying build a further retaining wall inside what is already there?
If so, would that need tying in to the inner wall already there (can that be done?)
Apologies again but thanks...

stuart45

weeg said:

You sure it isn't easier to just build more wall?

I would say it would be easier and cheaper to stick a 9 inch block wall behind it as gabion baskets aren't that cheap. People use them as a decorative feature, but I've never known them used behind a retaining wall. 

weeg

When you say build more wall are you saying build a further retaining wall inside what is already there?
If so, would that need tying in to the inner wall already there (can that be done?)
Apologies again but thanks...

Yes, that's exactly what I'm saying. build a 330-215mm thick wall behind it. I would tie it to the existing with drill in wall ties.

I've be told on here before that I over-egg my advice, which is probably true for a diy project. I design things in accordance with all the building codes, including factors of safety and all that. So, my designer head says '330mm at the bottom, narrow to 215 after a couple of courses of trench block'. My MSE head goes, yeah 215mm is fine. 

stuart45

I think it's better to over engineer, than under engineer with foundations, retaining walls etc. Very expensive if they go wrong.

Eldi_Dos

When our local supermarket was built on a site adjacent to a beach the car parking area was constructed by laying interconnecting crates (looked like upside down bread baskets/ beer crates), they were covered with a membrane and thin layer of hardcore and surfaced. Seven years later and a lot of traffic still looks as good as new. Must be good for drainage and reducing weight.

stuart45

Can be used  with this type of concrete.
Topmix Permeable Testimonial - The ultimate permeable concrete system - YouTube

boxa

Righty, firstly thanks again for all the replies so far, much appreciated.
I'm now going to go away, scratch my head a bit and work out how to start doing this - the biggest obstacle at the moment I think will be the other half letting me do it  
I'm almost certainly going to come back with quite a few more stupid questions as I can already hear them rumbling around in my head - hopefully you don't mind, it appears you haven't so far 
Thanks again and I'll be back soon,
Paul.