"Red Clay" determining concentration to build on

[AlanB]

So, I have a big hole where I dug to red clay to get a firm base to build my shop on.

The mixed and topsoil that we have is very squishy and not really the stable surface I want to build on.

Several folks have looked and said I could mix "some" soil in with the red clay and still be stable enough, but how do I determine how much is appropriate?

It was suggested to hire a soil engineer, but I was wondering what kind of actual "test" he would do, or would it be one of those things where Pay $500 and the guy walks out looks at the ground and says oh, about 1 truck soil to 3 trucks clay should be about right, evenly distributed...........

Anyway, anyone have some thoughts or experiences that they would care to share?

 

[crusty 1]

Alan,I built my last three homes and have had to do as you are doing.I was told to remove the top soil down to the [undisturbed] base.Not knowing how deep you need to go makes for a kind of hard answer.Kinda like the better half asking if her butt looks big in a pair of pants:laughing:I have had to remove about 6 inches to top soil and then refill with sand that gets watered and packed with a vibrator.Thats what has worked well here but you may have a totaly different situation in your local so I quess I,d follow the advice of a contractor in your area.It,s the kind of thing you don,t get a do over for so be sure rather than sorry.Just my two centsDave

 

[beppington]

500 bucks for an expert's opinion & probably stamp of approval doesn't sound bad to me, considering the amount of the investment that'll be sitting on it.

I've heard the horror stories of million dollar houses built on MS/ TN/ GA red clay, half the house sinking, the other half drifting away, etc., or with raised floors, having to jack them back up to re-level the floor every 6 months or so. Doesn't sound like a good long-term solution to me.

 

[dave1949]

What kind of foundation are you planning on using? Slab, footer, ??

No red clay experience, but some with yellow clay. Crusty's compacted sand method sounds good to me. Also, I think the clay may be more stable if the 'wetness' level is reduced and constant. So, good drainage around the foundation should help.

Due to it's inherent plasticity, clay is one of the worst soil types to build on. Stony sand aggregate is one of the best.
Dave.

 

[CurlyDave]

I have had very good experiences with a soils engineer.

He will understand the type of soil you have, its load bearing capability, and will make recommendations for they type of foundation you need. There are a lot more types of foundation than slabs and footers. There are piers, grade beams, etc. A grade beam can be flat on the bottom, or pointed. The different shapes will react differently to soils expansion.

Best of all, he will carry errors and omissions insurance, so if you follow his recommendations and the house sinks into the ground or splits in half, the insurance will cover you.

In general, I would never build without a soils engineering report.

 

[dmccarty]

Hire the engineer. If you have to ask the question then you need a good answer.

Our house was built by a GC with a PE. We wanted a slab even though one side of the house is only about 18 inches off of grade while the other side is about 60 inches. The foundation was built and then 67 stone which is rock up to about 2 or 2.5 inches with no fines was used to fill up the interior of the foundation. No compacting was needed. The slab was poured on top of the stone. Well 2 inches of foam insulation was put down first.

The slab has not moved.

I still was worried about the foundation because we have expansive clay in our area but it has been fine.

Spending a few hundred dollars to get your foundation done correctly is cheap.

Later,
Dan

 

[Chuck52]

After paying big $$$$ to "stabilize" my house foundation, I think if I were building a new house in this area I would pay the extra bucks to put in helical supports in the footing. This would be for a house or other big dollar structure because the supports would add significant cost to the project. Around my immediate area we have deep top soil in places all underlaid with clay. The companies that fix foundations sometimes drive way over 20 feet to reach the resistance they need to lift/stabilize a foundation.

Chuck

 

[sweettractors]

So, I have a big hole where I dug to red clay to get a firm base to build my shop on.

The mixed and topsoil that we have is very squishy and not really the stable surface I want to build on.

Several folks have looked and said I could mix "some" soil in with the red clay and still be stable enough, but how do I determine how much is appropriate?

It was suggested to hire a soil engineer, but I was wondering what kind of actual "test" he would do, or would it be one of those things where Pay $500 and the guy walks out looks at the ground and says oh, about 1 truck soil to 3 trucks clay should be about right, evenly distributed...........

Anyway, anyone have some thoughts or experiences that they would care to share?

Would a treated posts set in the ground every 6-8 ft apart, eliminate the need for a foundation? That is usually, how we build shops in Ky. Ken Sweet

 

[Steve_Miller]

Any soil base without proper drainage will not be good soil base, clay included. If you can't drain it then you have to replace it wth a proper base of rock or whatever to suit the weight it will be bearing, but it still needs to be a relatively dry base to be firm.

Steve

 

[rScotty]

Any soil base without proper drainage will not be good soil base, clay included. If you can't drain it then you have to replace it wth a proper base of rock or whatever to suit the weight it will be bearing, but it still needs to be a relatively dry base to be firm.
Steve

I have both education and experience building on expansive soils and agree with Steve. Yes, you can build on a clay base - particularly if the clay is well compacted, dry, and undisturbed. Sometimes there isn't any choice. You also need to know just what kind of clay that you have. Some are more expansive than others. Regardless, there are techniques that will work. BUT....and this is one great big BUT...just as Steve says, you have to keep the base material dry forever. That means putting a lot of thought and some money into good drainage and particularly not ever adding any water to the area. Large overhangs and double drainage to absolutely keep water away from the base are necessary. Lots of structures that are built on good hard clay/shale base are fine until some successive owner who isn't aware of the possible problem decides to extend his lawn right up to the structure. He puts down a foot of sod around the perimeter, waters it everyday, then the water travels down to the clay...and next thing you know the expansive clay problems start. There are ways to build even on known expansive clay - most methods involve piers or floating floor slabs or both. That said, don't let it stop you. Just build to take into account what you have and realize you are going to have to have to be smart about doing it.
A good non-technical book on the subject is "Foundations on Expansive Soils" by Chen. Probably out of print, but Abebooks.com might have a used copy. Chen knows his subject and is surprisingly readable. I just checked my bookshelf for my copy and don't see it. Probably loaned it out....blue cover.
rScotty