Stepped retaining wall - footer dept / reinforcement

[GinSoakedBoy]

I am planning on putting some footings in for a short retaining wall.

The ground is rock solid - I required a pecker on the digger to move the ground back a meter.

Working with the levels (house floor levels, subsequent decking etc) the footings would need to be 100mm to 150mm. Going any deeper on the footings would require significant effort pecking out a trench. It took a lot of effort bouncing around in a micro to get this far. Ground is very tough - 10 inches of soil and then its just rock all the way up the plot.

My question

- would a 100/150mm footing be adequate considering its being laid directly onto bedrock? Should I add in some fibres / or mesh to help with strength?

Dimensions

- The footer is currently 1200mm wide / 13m long (may be reduced as the wife has changed her mind slightly)
- The wall will be stepped - two rows of blocks roughly 1m tall and 500mm tall.

Before I put in a sizeable materials order I just want to sense check my approach is ok. Dont want to go through this effort & cost only for it to be a waste of time.

As an aside the last retaining wall lasted 60 years and was set on nothing more than a bed of mortar, so I suspect I will be fine. But I defer to more informed opinions.

Cheers

James

 

[Ivor Windybottom]

In my unqualified opinion, you can't get a better footing than that, there's absolutely no point in digging into it.

I'd jetwash it first though, blow the mud out and get a jagged rock base. As it stands, your concrete will only be about 25% in contact with the rock, the rest would have squidgy mud between the concrete and rock.

 

[^woody^]

100 will be fine. It should be twice as wide as the wall - more for stability than bearing in this case.

Fibres are to control drying cracking in screeds not concrete, and do not give a mix any strength anyway. You don't need any mesh.

Drainage of the retained soil would be important.