Ground is all sand, foundation questions?

[phalynx]

We bought a piece of property, beautiful with tons of Oak and Cedar trees.  The ground is a very very fine sand.  almost like ash.  The sand goes down for many feet.  In fact, I can't find anything hard yet.  I expect there is clay somewhere.  Several feet down, is sand.  I am planning on building the 2 story 20x34 but I am concerned about what foundation to build and how..  The land is in Central Texas so basements are not even considered.  I could do a slab or a pier and beam.  What should be reccommended and how?

thanks,

[Okie_Bob]

Suspect things may not be as bad as you say. The oaks you mention have to have something to hold onto as they have a substantial root system that has to support the weight of the tree. The cedar is not so well supported but, if the ground is as fine sand as you say, the strong Texas winds would blow the trees over.
Could it be you have picked the worst spot on your lot to build? Could you find another location what has something more like stable soil under it?
If not, I think you must have something solid under the surface. Does the sand become compacted a few inches or feet below the surface? I'm pretty familiar with the soils in a lot of TX/OKLA and find there is a lot of sandstone and clays all mixed together and have not run into a real fine sand that extends down many feet.
If you have that one location, I don't have a clue how to proceed but, bet there is someone on here that can get you started in the right direction.
Okie Bob, my .02 cents worth!

[glenn kangiser]

Sand is quite commonly used under slabs as fill because it compacts well.  Seems if it is contained well by a continuous foundation under a slab on grade there should be no problem- as long as it can't get out from under the slab.  You may want to see how others nearby have handled similar conditions and/or consult with a local professional.

[John Raabe]

I would also think that a reinforced slab would probably be the way to go. The Universal Cottage plans have two types of slab foundation plans. One of them will probably be pretty close to standard practice for your area. There may be some local modifications (extra mesh, larger rebar, etc.) that will be suggested by the builder, inspector or a local engineer.

Most places where people have been building for many years have accumulated wisdom about what works and doesn't work for local soils. Keeps us from having to invent wheels all the time.  

[n74tg]

Phalynx:
Where are you in central Texas; I grew up in Mexia.  

For all the rest of you guys on the forum; that's pronounced "Ma-hay-uh"

[phalynx]

Our property in about 9 miles NE of Elgin.  That's about 45 mintes East of Austin.  I would really like to use pier and beam so that I don't have to spend the money to get a driveway put in that can handle a concrete truck..  That's money I don't have right now.

[JRR]

I bet the local ready-mix guys know how to navigate on the sand.  Probably have all-wheel drive delivery rigs.  It would be worth it to at least give them a call.  You don't want concrete rigs on your finished driveway.

I'm from the flat Piedmont area of the Carolinas ... lots of sand ... no rocks, not even a pebble.  Slab foundations have become very popular there.  

100 years ago most frame houses were built on top of brick and mortar piers.  I guess the bricks were expensive, so there never was enough sq ft of pier footing to prevent sagging.  Never saw an old plaster wall that was not covered with major cracks.

[phalynx]

I should probably redefine my "driveway".  It's a clearing between the trees that I can drive my truck down.  At some point, I might add some hard dirt and MAYBE some gravel..  The sand is really soft and I bet would sink an 80,000 lbs concrete truck.  But, I will probably call one of the concrete places and see what they say.  Good idea.

[Amanda_931]

I spent a fair chunk of my childhood in the Sandhills of North Carolina.

Which in addition of sand had plenty of red--and a little white--clay.  and enough rocks, IIRC to put log cabins on.

[phalynx]

Ok, we were out there this weekend doing some more cleanup so I started digging in a different spot with my front end loader.  The sand is best described as sandy silt.  Very VERY soft.  I dug down about 24" and hit something different I was getting 4-6" of sand in a pass but when I hit this, I couldn't scrape 1/4".  It had a different color to it.  The best way to describe it is sand with a little orange in it.  When I hit it with a stick, it sounds like you are hitting concrete.  But, if you dig in it with a stick you can scrape up what I would describe as "thick flakes" which you could break up with your fingers.  After pouring some water on it and rubbing it, I would have to assume it is some kind of clay.  To me, I thought it might be sandstone, but I have been told, it doesn't exist around here.  

So, if it is clay, or not is just a question.  With the brief description I have given, and I am not holding anyone accountable, do you think I could do a post and beam construction if I go into this "substance" 2-3'?

[JRR]

That's probably much lower than frost depth in your area ... I would think it's ideal to "rest" upon. ... .  Maybe a cone shape concrete footing under each pier to make sure to get above any occasional wetness .. could be done with Sakrete if necessary.

[Daddymem]

You could do the contractor test.  Get it wet and try to ball it up then throw it at the contractor.  If it sticks, it is clay, if it doesn't it is silt.    

Seriously though, clay is just like you think, you can mold it, it has very little to no grit in it.  You can squeeze it between your thumb and forefinger into long ribbons.  If you can almost do all the above, it is a silt.  Snakes is another test, try making a long snake 1/8" diameter, if you can get it down that small and it still snakes, it is clay, else it is a silt.  All the aboves test have to be done on moist soil.  

If you were to look under a microscope, you would see clay in flakes close to what corn flakes look like, that is why they are troublesome, if the plates are all out of order the soil reacts one way, get it wet enough that the flakes settle flat to each other and the soil reacts in another way.  Silt on the other hand is very small but not flakes.

What you describe sounds very similar to a soil I found in Nantucket.  I call it Nantucket concrete.  This stuff looks exactly like the sand above and below it, but it is similar to flowable fill, you have to scrape at the stuff like a soft concrete.  This material is a fine sandy loam.  Loam indicates silt is in there.  Not that I have seen your exact soil, just a pot shot across the 'net.  

[phalynx]

Daddymem,

It sounds like the Nantuckett concrete to me as well.  This "soil" is very gritty when dry, very gooey when wet, but I don't think I can mold it into a snake at all.  I will try the contractor method (just to be sure  )  

So, the question is, the sandy loam, can it be used to support a pier foundation?

[Daddymem]

The question isn't can it be supported, it is how best to support.  Unfortunately that would be one for locals with experience or a foundation engineer, both of which I am not.  

[Billy Bob]

Phalynx, sounds like you might have hit some caliche.  You might take a sample to your local ag extension to confirm.
Caliche, hardpan, Nantucket concrete; all terms for a similar alluvial phenomenon.  The finer particulates leach through the soil until they find an agreeable settling point.  I recall some especially stubborn stuff in Georgia... even got a DI to admit it was unsuitable for foxhole digging! [smiley=wink.gif]
If you do have caliche, it may be a good thing.  One of the principle components of it is calcium carbonate, which they really do make cement from. Caliche is a component in road bed material, and is also the reason many of the early Native American earthen buildings are still around in the Southwest.

[Jimmy C.]

Estimating Soil Texture: Sandy, Loamy or Clayey?

http://www.ext.colostate.edu/PUBS/garden/07723.html

[phalynx]

I took a chunk of it into the office and asked a couple of people what they thought.  1st one said, that's clay, right off the bat.  The 2nd one said, that's clay, with sand in it.  Going through that flow chart posted by Jimmy, It's clay loam.  

[Billy Bob]

Hey, man, sounds like you have the raw material for cob building projects.
Have you checked out Glenn's cool cat stove, for instance?

[Amanda_931]

Apparently the dust bowl blew a lot of very fine silty stuff in here.  It's bad for a lot of things.  Needs sand and organic matter to grow much of anything, my spring silts up all the time, needs a couple of inches of hard rain to clean itself out.  What you can't do is roll it into a log, make coil type pottery in it.  Not good for cob--house or something like Glenn's oven.  Clay/sand can be very good.  Especially if it shrinks instead of expands.  The sand keeps it from doing too much of that.

And we've got clay veins around as well.

[phalynx]

Hum,,,  I hadn't thought about that.  I have been following Glenn's work for a while.  I might actually have to give it a try.  I have plenty of hay on my current property.  The new property is all woods.

[Amanda_931]

Straw will be stronger than hay.

[glenn kangiser]

The grasses will make a fine straw after they go to seed and just the stalks are left-- green is no good as Amanda says--- not as tough as rice straw but it will work.

[phalynx]

To bring back a point of discussion on this, I want to resummarize and ask the question differently with all of the answers.

On this property, we have a very fine sand for 12-24" and then is sandy clay loam.  It's a very hard clay.  I want to do a pier and beam construction.  The concrete guys around here won't venture on anything that isn't prepared and packed dirt.  They won't chance it.  So, I don't have the "real" ability to do concrete.  I don't have water out there at this time.  It will come later.  So, what I can do is do a method they use a lot down here for pole barns and such.  They put a little gravel in a 48" hole,  put the post in the ground and then fill the rest up with plain concrete mix, dry.  When you come back in a couple of days, the concrete is as hard as well, concrete.  It uses all of the moisture in the ground to set it.  It's worked well for my pole barn and other posts.  Now comes the question:

The 2 story house is gonna be heavy.  What is my best method for supporting it with pier and beam, on this clay, without traditional concrete.  I understand it won't be ideal, but I just need a "It'll work" method that won't "likely" collapse later.  Could I dig down and precast blocks under the posts? or just use a wide 18" hole? or what should I do?

[glenn kangiser]

If the dry concrete procedure is the common way of doing it there, then I would say away to improve it but still do the same would be to tie it together with rebar, and a bigger footing will support more weight.  I don't know what an engineer would say on this.

additional info--

I just pulled the plans to look this up and it is on the post and pier drawings.  John has an option with pressure treated wood and gravel with a treated double 2x12 bearing plate over gravel -- or an optional 16" dia. concrete footing with 2 crossed number 4 rebars under it as I mentioned above.  The dry mix would work -  i use it when setting posts sometimes - gets very hard too..  My engineer for the project I'm on now wants all steel 3" from the sides in the concrete so 3" con-mix under it then steel  then more concrete - just follow Johns plan - and if you have any question about your soil and are not getting an engineer remember that bigger footings and extra steel support more weight.

[phalynx]

Glenn,  Thanks for the reply.  I just looked at the plans.  I guess I missed the last page.  So, on this double 2x12 PT plate, would this just be 2 2x12x?? stacked on top of each other horizontally laying on a bed of crushed gravel?  If so, how would you tie the 6x6 to the 2x12's?  And, are you saying the substituting the gravel for the dry concrete mix might actually work?