New drainage pipes - backfilling

[mo-uk]

I am having a new soil pipe connection and and a rainwater gulley being put in.

2 quotes obtained - both will leave it so that the hole is ot filled in and I will backfill with mud and put a patio back on.

They will leave shingle under the pipe for building control to sign off.

One person has said that I should leave the work he has done for 2 weeks to allow things to 'settle' before I backfill.

Cannot see any justification for this.

They will be putting some concrete in as the connectiosn are close to the foundations of my house - so I wonder if it is the concrete that needs time to dry?

As it happens the work will be done on Wednesday and it would be Saturday earliest til I considered backfilling.

Also should I use the nciest soil/stone free as I can to cover the pipes up? Or shoudl I bung the nastiest soil down first so the ncier stuff is closer to the surface.

Thoughts?

[r896neo]

To be honest you'd be much better off filling it all the way up with clean stone or rubble and then capping it with 4 inches of lean mix concrete.

You will never be able to properly compact stuff in a trench so you want something that won't settle.

The pipe needs a good dose of pea gravel over it anyway for protection so i would just fill it with that and cap

If you need rid of the soil use the coarsest sub soil you can find and ram it in well with heels as you go. prtect the pipe with gravel as above first though. And i'd still cap it with leanmix

[mo-uk]

Is it OK to put say 10cm of 20mm or 40mm shingle on top of the pipe?

The geezers seemed to be saying that concrete on top was unecessary and would make future access harder.

[Dave_L]

Absolutely; there is no need to cover the pipes with lean mix/concrete unless they are especially shallow.

[seanandruby]

Concrete encasement depends on pipe type, pipe depth and if in road, drive, or softscape areas.

[r896neo]

Sorry i wasn't clear. Shallow pipes need protecting with concrete but the actual trenches (assuming they are more than 300mm deep) can just be backfilled with clean stone.

The capping with leanmix is nothing to do with protection its just that i find when trenches have been dug and then you have a drive or patio over them they are the weak spot for settlement and so can cause failures or dips in the finished paving surface. Therefore i prefer to throw in some lean mix as a belt and braces approach.

[lutonlagerlout]

same here simon
the BCO normally want deep pipes surrounded by shingle but a 150mm cap of leanmix near ground level is a good idea

cheers LLL

[mo-uk]

As per my other thread I have a load of 40mm shingle - can this be sued underneath and over? only concerned is some of them bits are quite chunky so possibly could damage the pipes I spose.

[seanandruby]

I would only condone the use of 40ish ml on concrete pipes over 300 dia'. It is usual to use 5 to 10 ml on 100 dia' drainage, or depending on material as dug can be used for cover in suitable applications.