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Boggy trench problem.


MikeSharp01

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I have been digging out the main slab foundations area for our passive slab and have found that the trench carrying services to the garden room at the back of the site, running under the slab from the utilities hub to the garden room about 600mm below slab base is very boggy. When I back filled it it was wacked down but still the digger tracks are sinking in if I track along it. I can only think that as it was a trench in heavy clay that the wacking has not been able to replicate 350 million years of compression and it has absorbed loads of the water we had in the early part of the year.  It is only about 450mm wide and I made sure that it is not anywhere near under the main structural points on the slab. Should I just pile more earth (clay in our case) on top and keep wacking, dig out and fill with type 1 and whack that or given that it will have 150mm of type one above it whacked down anyway to support the slab former just leave it alone. Any thoughts anyone?

 

 

20180518_172630+Line_of_duct_trench.jpg

20180518_172713_+_line_of_GR_duct_trench.jpg

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Sounds like the ground water is simply pooling along the line of least compaction. If the digger is making tracks in it then isn't that compressing the material in there anyway? What did you do, cover the services in sand / pea shingle then back fill with the clay you dug out?

 

I'd just keep driving over it and making up with the original clay.

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1 hour ago, ProDave said:

I would not be filling with any type of soil. If you want something to wack down you need type 1 or similar.

 

 

Me too.  I'd just allow for an extra thickness of sub-base where the trench is.  The sub-base needs to be whacked down in layers, anyway.

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4 hours ago, Onoff said:

What did you do, cover the services in sand / pea shingle then back fill with the clay you dug out?

Yes. Given above advice I will run the problem past the BC chap and prepare to use type 1. 

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Slightly different but when my brother had his drive & patio done I insisted he trench and lay swa to replace the "1mm pyro in a scaffold pole". Probably good for 15A plus when it went in and only to run freezer and a light but he wanted heaters and all sorts and to power his astronomy shed beyond. Plus it was down to earth anyway. The paving contractor really didn't want to do it but did. In clay, the paving sank along the trench line but the guy came back and redid it foc. 

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