Retaining Wall / Landscaping

[fishty]

Hi all, I'm new to the forum and am looking for some advice on building a retaining wall. Any advice you can offer will be greatly appreciated.

The scene:
My garden backs on to fields approximately 1m higher than garden level. My rear fence is at field level. At the rear of my garden is basically a big mound of dirt sloping from field level to garden level. This slopes about 2 metres in (approx 30* gradient) finished off with a small rockery of about 0.4m. It is not the most attractive of features and the soil / dirt is hard, full of rocks and basically couldn't grow a weed in it. The rear fence is approximately 10m long with a central gate onto the back field.

The intention
Build a two tier retaining wall with two planting levels. The first level about 0.6m and the top level about 0.4m. The wall will be split in the middle with steps going up to my back gate.

The Dilemma
I am totally unsure of how to approach the retaining wall. My idea is to use 215mm solid dense concrete block for both tiers faced off with a single skin brick wall. Is this overkill or would 140mm Medium dense suffice? I am planning for footings of 6-8" deep and 1 1/2 to 2ft wide - would this suffice? Also is it worth trying to tie the two walls together using wall ties?

The method:
Would it be best to do the lower retaining wall first then dig down for the higher retaining wall 1ft below the top of the lower retain wall for footings?

A possibility:
There may be a section of 3m where I do away with the lower tier and build part of the wall the full 1m height as I will be building a shed and pushing it as far back as possible.

Thank you very much in advance for any suggestions / advice.

[stoneyboy]

fishty,
Welcome to the forum.
Since you will be forming a different structure along 4m of the 10m I would suggest you make the wall full height along all its length.
Foundations will depend on the sub soil so you will have to trial dig to see if it's good enough for foundations.
Locate the foundation width so there is a boot at the back, use steel reinforcing rods which are bent to go up into hollow 215 concrete blocks.
Fill the hollows with concrete and incorporate wall ties for the facing brickwork. Use a polythene sheet behind the wall to keep it dry.
end

[fishty]

Thanks for your reply.

When you say a boot, can you please clarify what this is exactly - do you mean an additional line of block just on the first level?

Many thanks

[fishty]

I've just looked into a rebar application.

Can you please clarify something else for me? When laying a hollow block wall, do I still use mortar like a conventional wall or just lay the block dry - rebar - then fill with concrete? What mix should I use for the fill?

Thanks again

[stoneyboy]

fishty,
The foundation needs to be wider on the side into the bank thus forming a boot.
Use mortar to lay the hollow blocks (you may have to mix sharp and soft sand to get a firm mix) then fill the blocks with a wet concrete mix. The reinforcing bars need go into the first two courses you can add extra length from above once the wall is built.
end