shuttering and reinforcing a retaining wall.

1 Nov 2006
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United Kingdom
I'm putting two 21' long walls down a slope, about 1m high, separated by steps 1m wide. It's "sort of" retaining in as much as there will be 4ft height of soil behind it, but in reality the soil has been there and stable with no retention for the last 70+ years!

However - I'd like to be on the safe side so I've dug out 18" x 18" footings, stepping down the slope 18" every 3'. the walls are "S" shaped. I'm going to build the walls in 9" hollow block and stick rebar in before concreting, then face the walls with stone.

2 questions:

Firstly, what's the easiest way to shutter the footings given the curvature (radius of curves is around 3m for the majority, tightening to a radius of just 1m at the bottom of the "S". I only need to shutter the facing edges to a height above ground of around 9 inches (steps going in between walls will be at this height)

Secondly - Do I need to add rebar into the footings to stick into the lower course of blocks, or am I really going overkill here?!

In fact, am I going overkill full stop? Total distance from top of slope to bottom is 21' with a drop of 10'. Gradient must therefore be around 25 deg?
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why shuttering.

surely it is simpler to dig the footings INTO the soil or below ground level, so that the soil is the shuttering?
it would and it wouldn't....

yes it would get around the shuttering issue, but it would also mean a lot more soil, another skip (of which to get to I have to carry the soil up the slope in buckets, put it in a wheelbarrow, along the patio, up 3 steps across the drive onto the road, down a 1:3 hill and hope I can stop when I get to the top of the ramp on the skip...)

It would also mean more swinging the pick axe to get through the large sized gravely stuff I hit after a foot depth. Which I'm fed up with. :LOL:
forming shuttering is a moderate- difficult job, even to build in straight lines. especially knowing how sturdy it needs to be to retain concrete.

forming curves is tough work.

sub soil dig for me every time.
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yeah must admit shuttering up the house footings last week was not exactly the most enjoyable experience, was just hoping someone would have a simple suggestion to reduce digging - as it's > 50% below ground level already I was hoping it wouldn't need too much support.
wet concrete behaves like a liquid.

a very heavy liquid.

for shuttering to work it needs to be sturdy and contain the concrete well.

there are no easy ways to construct curvy shuttering.
oh well, guess I'll have to make the effort to do it properly then!
If its only 4' tall then a 6" x 9" block laid flat will be fine. No need for shuttering. If you don't like handling a 6" block then use a 4". (I know they are metric now but have always distinguished them this way)

The S shape that you are going to build into the structure will add an immense strength also.
However the problem you will be faced with is topping the wall to run in line with the inclined gradient as you have stepped the foundation.

I would build up to the points where the blockwork is level with the finished incline and finish out the rest with cheap 13mm plywood hilti nailed to the blockwork for speed. You may need a few tie bars and you could use 13m threaded bar zipped through and a few 3" x 2"'s to act as strongbacks.
Cut the plywood into strips sized depending on the incline angle gradient and the foundation step.
Then fill out the top with concrete. Easy. ;)
Many thanks Norcon :)

Must admit I've never used 6x9's - they sound heavy :LOL:

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