shrink - swell soil stuff

[pforden]

Hi,
We're trying to avoid expensive engineering fees in Central Texas, choosing a site on our property to put the house. Clay soil is a huge issue in the area. We have two areas on the land that are supposed to be okay for houses without basements, some loamy fine sand and some deep fine sand. I thought I had read a test where you dig a hole, pour water in, come back 24 hours later to see if the water has absorbed... most likely this was for the septic, but, anyhow, I am wondering if there is something simple or inexpensive we can do that will tell us with some degree of certainty that we can build on a particular site?
Otherwise, assuming we have to get an engineer to do this for us, has anyone hired an engineer for this purpose? ideas of costs?
Thanks.
Penny :question

[jraabe]

What you would like to know is the bearing capacity of the soil and how likely it is to expand when wet and/or frozen.

I have been trying to come up with a simple test for bearing capacity. The idea so far is to take the tire of a car or truck of known weight and have it bear down on a small block of concrete or metal and measure the soil penetration over time to test the compression of the soil. To be truthful, I haven't come up with anything yet that I would trust for much information.

Your building department may have guidelines as to bearing capacity based on the soil color, structure, etc. Many building departments develop this information over time through experience working in local soils.

One simple test you can do for expansive soil is to fill a jar 1/2 full of soil from the footing area, tamp it down firmly and mark the side of the jar. Now add water to the soil until it won't absorb any more. Let it sit overnight and see if the soil level rises. Mark this if it does. Now, stick it in the freezer overnight. See if and how the soil expands. Mark that soil level.

If all three marks are very close together you are unlikely to have problems with expansive soils.

[glenn-k]

Another telltale sign of highly expansive clay is that in the summer you will get cracks in the soil - some places I have seen have 3/4" wide cracks in the ground every foot as it dries in the summer.  I guess that is only good if you've had it a while.

[pforden]

John and Glenn,
Thank you for your replies.
These both sound like helpful ideas. During late March we will look into this. I am going to look at our photos of the property taken a couple of months apart, with the area moving into severe drought in that time. We have some pretty close-up pictures of the area where we are thinking of building, and it is excavated there for a livestock pond, so bare ground shows -- most of this is highly improved pasture at this point, so it would be hard to find any cracking. Our next door neighbor, also building now, hired an engineer and is getting an engineered foundation. I am not certain what conditions are prompting that or if his contractor just uses these foundations as a standard in the area.
Of course, this is SE of Austin, Texas... not a lot of freezing and thawing of soil, I would guess, but the drought conditions may have quite an impact.
I'll let you know what we find out.
Penny