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Concrete Slab Foundations - Best Practices

Tips for Building with Board Form Concrete
Published on Apr 29,
The most common foundation in the South is a Slab On Grade. In this video Matt will give you an overview of the process as well as some Best Practice tips you can use on your #BUILD!

How to Build a Foundation on Piles

Tips for Building with Board Form Concrete
Transcribed Video Published November 4, 2016 on YouTube

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If you're planning a lakefront build, I'm going to show you how to do a steel pile foundation. Our company is just starting this beautiful new home here on Lake Austin.  We're working with Shiflett Group Architects and I want to talk to you about the foundation that we're doing for this very special lakefront house. As you can see, we've got a beautiful flat lot here and it drops onto Lake Austin. Beyond us, Lake Austin is a man-made constant level lake. We're right near downtown Austin and the beauty of that is we don't have to worry about the rising and falling water levels.  However, the downside of this property is we've got a water table that's just a few feet below my feet right now.  If I were to dig a hole right next to me here, about four feet deep, it would start filling up with water.   And the way that we deal with that on this particular lot is we're going to be using steel piles.   Anytime you build a foundation the first step is always going to be to get a geotechnical engineer out to do a core sample for you. And when he came in corded this lot, he drilled all the way down until we hit rock just a little over 50 feet deep. What we found was good soil the first couple feet and then very super soil from that water table all the way down until we got rock.  

So, steel piles were the recommendation from the structural engineer.  Here, so let me talk about how this works.   When we get finished this is going to look like a very typical slab on grade foundation but the steel piles are really going to be doing the heavy lifting of supporting this foundation. Here's how we do those the steel piles.  They are put in by a pile contractor.  The first step on installing these steel piles is the drill about a 10-foot deep hole and that's going to give us a starter for these columns. Now these steel piles they come in about 30 foot length. There are three eighths inch wall steel and there about eight inches in diameter.   And before we start driving these we're going to well to cap, we don't want to have that column fill up with either water or mud. We want to keep that column free so we can fill it later with both rebar and concrete.   So, the first step after we drill that then is we're going to drop that first pipe in. And you'll notice when the forklift comes that first 30 feet goes down like nothing. All we're going to do is just press it down with the forklift.

Now, I mentioned rock was 50 feet and depth and these columns come in 30 feet so once we're just a few feet out of the ground that first column, we have to bring another column.  And well these two sections a column together and then we can continue pushing that once we get to about the last five feet or so.  Before we hit rock, the forklift can't do it any further and that's where we need to bring in the pile driver.  In this case, we're using a crane supported piledriver which is going to drive that steel column all the way down until it hits refusal.   In this case, we hit rock between about 55 and 60 feet in depth and so now these steel pounds, once they hit rock and hit refusal each one of them can hold 300,000 pounds of bearing capacity.   Very, very impressive.   The engineer designs these in a very specific grid pattern so that our point loads from the house onto the slab are distributed to these piles and now in effect our house is floating above all that super miss below us.  Now, the steel piles are in place for both the house and the landscaping.  

We're going to bring our concrete crew, Boothe Concrete, to be forming up the house slab and we're going to integrate the house's rebar into the steel piles.  We will come back in a couple weeks and we show you the progress.  Ok, we're back it's been a couple weeks and as you can see the Boothe Concrete guys have done a fantastic job.   We're just a few days away from pouring the slab, but let me show you now that we're set how we've integrated this concrete slab in with those steel piles that we drove.   So, remember last time we drove those piles all the way down to bedrock and you'll notice those piles are at the bottom of our beams.  If you're not familiar with the reinforced concrete slab, you typically think of your slab thickness is just a few inches.   In fact, this will be a 5 inch thick slab but all the strength from the slab comes from the beams.   That's that grid pattern you're seeing.  It's deeper all the way through this foundation inside those beams.   We've got a rebar layer that's going to integrate into the concrete and stiffen the slab and give it strength.   And at the bottom of the beams, that's what that steel piles are going to be.  

Before we got to this point, we filled those steel piles with concrete and then we've got rebar sticking out.   And that rebar is going to integrate into our slab rebar so that now we've got this grid pattern of beams.  At the bottom of those are piles and in fact, the entire concrete slab is going to sit on those piles.   Each one of those piles can bear 280,000 pounds of bearing so we've got several million pounds of bearing capacity on that steel.   Now that we're all set is a really impressive foundation. If you're not familiar with the yellow plastic, that's our vapor barrier. We're using 15 mil stego wrap here that's going to keep any moisture that's in the soil from getting into our concrete.  And now when we pour this next week, we'll cover it for a few days and then we'll be ready to move on.   You know you want to spend the time and the money on your foundation right because no matter what you do on top of your foundation, moves are going to have big problems with your house.   This is the best way to do it if you've got really bad soil.  I highly recommend you talk to your engineer, your builder, and/or your architect about whether steel piles might be an option for your property.

How to Build Board Formed Architectural Concrete Walls

Tips for Building with Board Form Concrete
Published on Nov 6, 2013
It has texture, structure, and rugged beauty all at once!
Architects love it, but it's not an easy detail to get right. Watch to see how my Concrete Craftsman do it right. I'll show how we formed these board formed concrete walls including tips on wall ties.