Backfilling with wet clay

14 Oct 2012
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United Kingdom
I have finished laying the underground drainage outside and have backfilled with about 50 cm of clay. However, it is very soft due to all the rain and is currently like walking on a sponge. The drain is in the garden and will only be walked over. I will either put top soil back or pave.

What is likely to happen to the clay backfill over the winter and is there anything I should be doing? The backfill is over 100mm of pea shingle over the plastic pipe.

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is there anything I should be doing?

Nothing. It will eventually settle.

Have seen us concreting 200sq/m over soft backfilled clay 1.5m deep. No heavy loading on it but it will eventually drop and sink and the concrete will crack.
we had a kitchen drain put in 2yrs ago backfilled the same, although only short run so everything was just piled back in and stompted on.

This week we have lifted the turf that was put over and laid some slabs. It was very obvious where the trench was and walking around on the clay made it sink an inch or two without any effort. (bearing in mind the amount of rain we've had lately too)

As we were laying 2inch, 3'x2' slabs (in the rain!) and only for foot traffic its not going to cause us a problem bridging over it in effect, but I certainly wouldn't lay a block paved drive on it.
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Thank you for your replies. Not only did the trench not collapse I can now forget about it over the winter. :)

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