Fence posts in fresh backfill

[John T]

Hi, I have built a 1.5M high containment wall composed of 6inch blocks laid on sides, cemented half bond, sloping in at 1/4 bubble, top course 6ins on edge, internal pillars every 2M and externally buttressed on old concrete link fence posts.

The ground is garden soil down to 1.25m then clay and shale following an old dry watercourse. Backfill is a mixture of  foundation shale & clay/soil mix topped off with 1/2m soil.

There is gravel drainage along the bottom inside of the wall exiting at one end. The soil area is bounded by pathway approximately 2.5M parallel with the wall and surface water drainage piped clear of the area.

I would like to construct 5ft high fencing where SW strong winds blow face on at the retaining wall and fairly sheltered from the soil side

Questions.

1 How long should I allow the soil to settle and firm up before posts are erected?

2 How near to the top of the retaining wall should the posts be set, I would prefer 1 ft, vis a vis the constructed weightiness of the wall?

3 How deep should the posts penetrate below ground to cope with high gusts?

4 Would concreting the posts allow for shorter ground penetration?

5 Is there a system for concreting in posts that allow easy removal/replacement with good drainage of post ends to reduce rot?

6 Are there any modern posts that have long life, UV proof and are well regarded in the fencing industry?

Still getting to grips with DIY at 74. Regards John

[Pocster]

I had a slightly similar issue. I wanted concrete fence posts but all my ground had been dug out and would be back filled ( underground house ).

I was worried the 'earth' wouldn't be solid enough. So I shuttered the length I needed and plenty of depth. I then placed chucks of PIR insulation where each post would go ( with some allowance for play! ). From memory I wedged / screwed them in situ to the osb / scaff board shuttering.

Then got a lorry load of concrete pumped in along the shuttered trench.

 

Not sure if that's the best way to do it!. Once concrete cured fixing the posts was easy ( more work trying to get the PIR out ). Concrete posts have been up 4 years now - not one has moved. Hope my explanation is clear.

Edited January 31, 2022 by pocster

[Pocster]

Also I used 'lite' weight concrete posts. Cost a bit more but much easier if you are doing it on your own.

[Carrerahill]

Whatever you do, if using wood, hardcore in the holes first, compact it a bit, then the new fence post should sit hard on the hardcore, then top up around it with more hardcore, then add concrete. This stops the post sitting in a socket of water for the rest of it's life and they last much must longer. I always trowel the concrete at the top to slope away then backfill with more hardcore or decorative gravel. 

Edited January 31, 2022 by Carrerahill