Retaining wall foundations

[mercury]

Was wondering if anyone can advise me on the size and depth of concrete foundation for a 400mm-500mm high double brick retaining wall (which will be holding soil back).
Also if red engineering bricks are ok to use or will they lose there brick faces after a period of time.

Thanks

 

[noseall]

make sure the foundation has at least 150mm projection each side of the wall. in other words a 225mm thick wall will require a 525mm wide footing. this should be at least 225mm thick.

if it is a retaining wall, you can back the wall in with solid dense concrete 7n blocks, where they won't be seen. you should be ok with red engineering facing bricks, though this is no guarantee against perishing. i have seen walls with poor quality reds that have blown faces.

giscol commons are a good walling brick

 

[ColJack]

very helpful post..

so a 2 foot wall only requires a 1ft deep foundation?

I need to build a similar wall

I was going to use concrete blocks set on the side as the retaining wall up to the higher ground level, and face it on the low side with regular bricks and a pillar every so far for looks..
the facing brick wall will continue above ground level becoming a double wall on top of the blocks to act as a safety wall to stop kids falling off the extended patio...

 

[noseall]

the concrete thickness should be around 9 inches minimum. the actual depth of this concrete footing will depend largely on the ground conditions.

2 feet down (600mm) should be a minimum, going deeper if the ground conditions dictate i.e. non virgin soil, building site debris etc.

 

[ColJack]

ok, you're confusing me a little here.. I'm an electrician not a builder..

are you saying that the foundation has to be at leat 9 inches thick, but has to be 2Ft into the ground? IE a foot of my wall will be under the ground level?

can you help me on a few calculations too..

if the foudation is about 6 meters long 600mm wide at the depth you say, how much concrete will I need and will i be best off getting it in a truck rather than mixing by hand ( factoring in cost of materials and hiring of a mixer? )

would I need any re-bar in it also?

 

[noseall]

if the foudation is about 6 meters long 600mm wide at the depth you say, how much concrete will I need and will i be best off getting it in a truck rather than mixing by hand ( factoring in cost of materials and hiring of a mixer? )

would I need any re-bar in it also?

6 x 0.6 x 0.225 = 0.81m3.

this equates to about 1.5 tonne of ballast and 10, 25kg bags of cement.

for this i would normally use my belle mixer, but it's up to you. maybe a mini mix company could give you a quote? logistics is the biggest problem with readymix. no need for re'bar.

 

[mercury]

Great info

When using concrete blocks, can they be set the usual way (same as an internal house wall) or do they have to be used set on the side as the drawing above shows for a retaining wall.

Also the soil is compacted clay so would i still need to go down to two feet.

 

[ColJack]

i'm only using them on side for added strength.. no idea if i have to or not that's just the way i thought of doing it..

 

[Static]

Lightweight concrete blocks tend to shatter in frost conditions and are unsuitable for below DPC. Either go for engineering bricks or 7N blocks preferably med dense/dense where the wall retains then you can change to normal bricks.
Put in 50mm dia weepholes every 1.5m or so.