I am building a 20′ x 30′ shop space and doing my own foundation work. I will be pouring a footing and a 4′ frost wall with a thin slab to serve as a crawlspace for ductwork and electric. The site has been excavated. The base for the footing is clay that, as the groundwater seeps in from the sides, gets softer and softer. Convention in these areas is to pour the footings as soon as possible even it’s in a soupy mixture of clay- the reasoning that the concrete will displace any water and find its own hardpan base. With limited foundation experience this still seems a bit suspect. Would it be better to lay down a foot of crushed stone or gravel, compact it and proceed from there with a drier base? Or should I slog through the clay?
Edited 5/11/2003 6:58:49 PM ET by atbuild
Replies
Atbouild,
On all the pours I've worked on we pumped water out for two to four days if posssible... If not, we would pour concrete soup and use that for a base and doubled the width of the footing.
Soup recipe = 1/2(-) gravel at a three bag mix wet enough to self level poured 1" thick.
BBUUTT, I think you're building a 4' deep indoor swimming pool under your shop because concrete is NOT watertight. Build in some proper drainage, maybe Form-A-Drain or gravel and perf'ed pipe.
Convention in these areas
Does it work?
the reasoning that the concrete will displace any water and find its own hardpan base
Seems to me that the only way the concrete has to find hardpan is to settle to it over time??? ...But I'm only a 12yo steelin time at mah daddy's 'putor. You never know.
What kind of shop are you building? What flooring system? just curious.
SamT
Situation like that - I like to get at least eight inches of stone tamped in ther first.
Excellence is its own reward!
The best advise is to contact either the local building inspector and inquire within, or locate a reputable foundation company that is experienced in your local. Or even better yet, contact an engineer and have him/her write you up the proper specs for the foundation. "One measurement is worth a thousand expert opinions"
I would agree with Woodrow. Find yourself a Geotechnical/Foundation engineer.
Peter