Retaining wall, planting and patio

[Parksyp]

Hi All,
I am using lockdown to do some long needed changes to the garden. I am replacing and pushing back a victorian brick retaining wall and want to incorporate some planting between it and the patio that will sit behind it.
The wall will be less than 700mm high. I am intending to incorporate drain and drainage gravel to take the water away from behind the wall although I have had is suggested that this is overkill at this height. Would do it properly though..
I am intending to use 7KN solid blocks for building the wall. 
I have a couple of questions.
1. Am I ok to use compacted MOT1 for the foundations rather than putting in concrete foundations? I have read that it is better than concrete for retaining walls but some people say that you should use concrete. I am intending to use a type 1 base rather than concrete because of the limited height of the wall.
2. What is the best way to create the planting space between the wall and the patio. To my mind either the front or the back of the planting could be the true retaining wall, with the other side being purely to contain the planting area and to edge the patio - which will be pavers. I have attached a couple of plans of how I think it could work but would be grateful to get some thoughts and experience on this. I am keen to avoid over-engineering the wall with two full walls just to have some small planting along the edge of the patio, but also don't want the edge of the patio to start moving after a few years. I would rather be clever about rather than just throwing lots of concrete at the problem.
3. How stable is drainage gravel? If I am putting this behind the retaining wall then the patio edging will be partly on top of it. Could this cause a problem or does it compact well enough to give the support to a patio and the patio edging/back of the planting?
Any guidance appreciated. I am keen to and enjoy doing the work myself but like anything there is no replacement to bringing experience to bear on a project like this!

 

[Declan52]

Ok.

1. If the retaining wall will be made from concrete blocks then it's going to need a concrete foundation. If not it will sink slightly and the bond of the wall will break. There are dry retaining walling that needs no concrete available. 

2. You can use timber like a railway sleepers to form an edge or a concrete kerb. 

3. The edge of pavers needs bedded with mortar/concrete to stop it pushing out as you walk on it. If the edges aren't solid the paving spreads. This can be be on top of well compacted hardcore. Drainage gravel and hardcore you use to form a patio area are completely different materials.

Using concrete is not over engineering a solution, it's using the right material in the right circumstances. Sometimes it just has to be used.

[Temp]

I wouldn't just use MOT for the foundation either.

 

I have one low height from railway sleepers laid flat and even used concrete for that. I predrilled holes in the sleepers and put the bottom ones down while conc still wet and pushed rebar through into the concrete. 

 

Elsewhere we have the walls in the photos below. We put drainage on both the uphill and down hill side. At the foot of the wall we put a linear drain that drains the patio and collects water coming through the wall. The curved beds are single brick on concrete founds. They have a drain at the bottom and pea gravel.

 

All bricks and blocks should be FL (frost resistant).

 

Yes I know patio needs pressure washing and some moss killer.

 

 

 

 

 

[Parksyp]

Hi Declan,

 

Thanks for your reply. I have amended the drawing to reflect what you suggest. (I think!)

 

So - to be clear - even concrete blocks on compacted type 1 isn't good enough - you would always use a concrete foundation?

 

Is the foundation and the block wall to the edge of the planting and patio overkill? ie is the area shaded blue excessive? It obviously isn't retaining the mass of earth but needs to support the limestone capping stone that runs alongside the pavers.

 

Thanks again for your help and experience - really appreciated.

[Conor]

I'd never build a wall without a concrete foundation. It'll fall over eventually.

 

Line any face of the wall that in in contact with oil/water. Really think about your drainage and make sure water can move freely away from the back of the walls

[Declan52]

Just bed the capping stone on concrete. No need to do more foundations and build another wall. Well compacted hardcore then concrete then your capping.

 

[Parksyp]

26 minutes ago, Declan52 said:

Just bed the capping stone on concrete. No need to do more foundations and build another wall. Well compacted hardcore then concrete then your capping.

 

Thanks Declan - that is really helpful.

 

And thanks all for all the answers and convincing me to go with concrete foundations. 

[Parksyp]

4 hours ago, Declan52 said:

Just bed the capping stone on concrete. No need to do more foundations and build another wall. Well compacted hardcore then concrete then your capping.

 

Hi Declan,

 

Further to what you were saying I have sketched out how I imagine that might work - see below.

 

Do I need something to contain the hardcore that the capping stone is going to be sitting on? I want to have soil for planting on the left of it and without more of a wall won't the hardcore 'escape'?

 

[Declan52]

The soil will stop it going anywhere.