The next project I will be tackling is the construction of a fence across the front of the house on the roadside. The requirements are that it be a height of around two meters (possibly a bit more at one end) and provide a visual barrier.
Currently I have a solid retaining wall in concrete at ground level for about 20 meters, it looks pretty solid and has no cracks in it. It has been there for I would estimate at least 30 years. And the remaining 10 meters of low block wall that has cracked at one end.
I am thinking of doing something like this, but I am uncertain about many aspects of it so I welcome any suggestions, even a complete redesign.
Remove existing concrete posts and old fence.
Repair low cracked wall by shuttering reinforced concrete on top of it, entire length of that 10 meter section.
Continue at the new height of the reinforced section in 20x20x50 lightweight block with a reinforced band of concrete or 'chainage' on top. This would be build upon the existing ground level retaining wall.
At this point I would have a concrete wall of 20cm thickness 30 meters in length by about 40cm at one end and a meter at the other (ish) Will have to measure that.
Continuing above to 2 - 2.4 meters in timber using class IV posts 150mm x 150mm and 215mm x 45mm x 2 meter horizontal planks.
They are solid blocks, quite old. I could drill into them and chem fix some 10mm rebar along the top to link in with the chainage. But like you say that may not be enough to hold the load above especially the wind overturn consideration, we get some pretty high winds here on occasion.
Perhaps a rethink is in order?
I could just repair the wall and then plant the posts in the ground instead? How deep would they need to go?
There are no weep holes in that wall.
I wasn't sure how to fix the posts to the top of the wall yet either and as you have expressed concerns with wind overturn I'm not sure at all!
James, few comments and then it's up to you really.
Starting with the block wall. Will that method of repair be stable, ie just pouring ontop? For me you would need to tie it back to the existing low wall. Do you know if the blocks are actually hollow or if they have a concrete fill. Hit the top in one or two places with a ball head hammer and see. If they are hollow, you could get some rebar in there and seal them in with your concrete to give you some starter bars for the blockwork above. If it is already solid and cracked, I'd consider taking out the smaller of the damaged lengths and rebuilding it, tying it back to the remaining. Would still advise (if solid) dowelling some starter bars into the top of the wall to build your new block off.
The other thing I'm thinking of is: if your low walls already have a small amount of pressure on them from your garden (not much I assume), if you build up your 2m, will there be the possibility of a wind load overturning the lot onto the road? You do have weep holes in the retainers do you to relieve the ground pressure ? Not that important though given the amount they are currently retaining.
For the other side, the concrete wall: again if you are going to build this up in block first, you need to tie it to the existing structure (dowelled starter bars - in effect creating a chainage in the block).
For your post brackets will, the base plate sit within the width of the wall - I couldn't check this. Would there be the other possibility to fix these brackets on the top of the existing walls and then build up the reinforced blockwork around them, finishing with either a concrete cope or a render, giving your posts a bit more stability, put a mastic joint between the post and the cope/render finish for a) weather proofing and b) a bit of flexibility. Again the wind load overturn factor still worries me.
Last, I would assume if you are using 45mm thick rough board, this will give you your stability between posts.
