Retaining wall and fence - advice please

21 Sep 2007
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United Kingdom
I need to replace this beautiful fence:
It's in a pretty sheltered location, as you can tell by the fact that it's still standing! There is a short length of wall, which retains my neighbours raised bed. The main part of this wall runs acros the neighbours garden perpendicular to the fence.
My plan is to dig down to the foundations of the wall, replace the two posts in the picture with extra long posts, and then extend the existing wall to fill the gap between the posts. Then I can put a standard panel resting on top of the wall. I've assumed that wooden posts would be a silly idea here - the right hand post will have soil against the bottom two feet and will be a nightmare to replace. I've found 3m concrete posts at which will be just about long enough. 3m posts seem to be pretty rare in standard 3" / 4" sizes, I'm a bit worried that concrete posts that long are a bad idea? I can get heavy duty 5" ones, but they're very expensive and heavy, so I'd rather not.
1. Is 2.4m above ground / 0.6m under, too long for a standard slotted concrete post?
2. The wall and post will be retaining a 400mm high bed, does the wall need to be double skinned? The existing wall looks to only be single skin at the end that I can see.
3. Should I build the wall round the back of the post to retain the earth and take the pressure off the post?
4. My plan is to dig the footings for the wall, then dig a post hole in the bottom of that. Concrete in the post, then pour the footings round it. Can I do it all in one go, or should the post hole be allowed to go off first?
5. How do I go about drainage behind the retaining wall? Can I rely on whatever they put in the main wall in my neighbours garden? If not, should I leave gaps between the bricks at ground level? I plan to build a patio in the area, could I build a drainage channel against the wall, under the patio?

Apologies for the long post... Any tips gratefully received.
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