Digging with high water table

[ProDave]

12 minutes ago, Macfracam said:

The insulated slab we are looking at is extruded PS so is meant to be completely waterproof, helping if the water table rises in the winter.

I am not sure I would want an insulated EPS raft foundation below the water table.  EPS floats very well......

[G and J]

2 hours ago, ProDave said:

I am not sure I would want an insulated EPS raft foundation below the water table.  EPS floats very well......

Good for peeps named Noah perhaps….

[Iceverge]

I like the idea of trench fill foundations here. 

 

Mainly because you could dig and pour them in a few hours if you had a good ground works team and digger man.

 

Thinking out loud here and assuming the site is very wet indeed......

 

I would get a digger in and dig 4 trial/monitoring holes onsite well outside the foot print of the house. Based on the advice of your engineer I would agree a depth for the bottom of the foundations.

 

Then monitor the water level in the holes. When you were confident it was low enough, and there was zero rain forecast swiftly get a digger in, dig the trenches, consolidate the bottom, drop in some rebar and pour the trenches off a laser level. You'd only need a window of 2-3 dry days. 

 

It would need nothing near the level of accuracy of a raft or insulated raft and you'd be out of the woods regarding the major risk of the ground turning into a quagmire. 

 

I wouldn't even get rid of the topsoil beforehand as you'd be exposing yourself to getting caught out by a shower of rain that could turn your site into a swamp. That could all be done after the foundations were poured.

 

Even if the top of the foundations weren't perfectly level the imperfections could be taken out with a secondary pour or some blockwork. 

 

Someone please tell me why this wouldn't work.