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We have undertaken a project is in Irving,TX. We gather that soil is rather fragile, heaves and there is lot of moment. Owner had almost six inches in the last decade or so - driveway dropped six inches from the foundation level.

To build a strong structure, we have decided that four piers be installed on each side, including the steps. Here are some pictures of the current state and idea board of how the driveway could look like..

old sunken driveway :
https://postimg.org/image/9bg5wm4fh/
https://postimg.org/image/87w1knjsd/

current state :
https://postimg.org/image/hpr76yg31/
https://postimg.org/image/6et4wbylp/

Owner would like 6" slab, 6" gravel, since the old one was a floating driveway should we attach the new driveway using dowel to the foundation ? Getting many mixed suggestions. The house is around 25-30 years old. House itself seems to be in a relatively good state.

Good pointers on what to consider and how we go about would be greatly appreciated.
 

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I assume you have expansive clay there, just like around Dallas. 6" of gravel isn't going to change that. If you don't want it to move, you'll have to take all the expansive clay out and them put in your gravel and slab.

Personally, I'd never pin a drive to a slab in an area with expansive soils - either the house moves or the drive moves, or both.


If the drive dropped 6 inches, I'd guess there is subsurface water washing the soil from under the drive slab. You have to do some homework to figure out if this is the problem or not.
 

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If the drive dropped 6 inches, I'd guess there is subsurface water washing the soil from under the drive slab. You have to do some homework to figure out if this is the problem or not.
That's kind of what I saw from the first pics....hard to tell. See what you can get by shooting a line from the garage to the curb....faster you can drain the water the better. Roof drainage/ downspouts a factor too. The lot just looks like one of those where water is a problem
 

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We have undertaken a project is in Irving,TX. We gather that soil is rather fragile, heaves and there is lot of moment. Owner had almost six inches in the last decade or so - driveway dropped six inches from the foundation level.



To build a strong structure, we have decided that four piers be installed on each side, including the steps. Here are some pictures of the current state and idea board of how the driveway could look like..



old sunken driveway :

https://postimg.org/image/9bg5wm4fh/

https://postimg.org/image/87w1knjsd/



current state :

https://postimg.org/image/hpr76yg31/

https://postimg.org/image/6et4wbylp/



Owner would like 6" slab, 6" gravel, since the old one was a floating driveway should we attach the new driveway using dowel to the foundation ? Getting many mixed suggestions. The house is around 25-30 years old. House itself seems to be in a relatively good state.



Good pointers on what to consider and how we go about would be greatly appreciated.


I deal with expansive clay often. Here's what my engineers have me do. First I soak the clay to get it expanded. ( I mean saturate it for a few days) Dig 2'x2' (minimum) structural footings all around. Then use #3 rebar both directions at 18" each way.4- #4 bar in footings with slab bar tied to footing bar. Pour on wet expanded clay using 4500 psi.

Edit: Soak pad after footings are dug.

This was an engineered slab on grade with really bad clay.
 

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if you have that much settling do not dowel to garage slab unless it has been engineered to carry the load.

an engineer can design a structural "floating" slab for your site conditions.....but....

your clients WILL not like the price....

and you will not like what is involved in building it....
 

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I deal with expansive clay often. Here's what my engineers have me do.
Where the OP is, there probably isn't 2' deep expansive soil before he hits hard pan. It's like that in lots of places in Texas.

The hard pan can and does cause soil movement from the subsurface drainage over the hard pan. The house slab footing is probably down into the hard pan. If it wasn't, and it's not isolated from the expansive clay properly, the slab would be cracked all to pieces by now. At least that's what I've seen in Dallas and Austin.
 

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Where the OP is, there probably isn't 2' deep expansive soil before he hits hard pan. It's like that in lots of places in Texas.

The hard pan can and does cause soil movement from the subsurface drainage over the hard pan. The house slab footing is probably down into the hard pan. If it wasn't, and it's not isolated from the expansive clay properly, the slab would be cracked all to pieces by now. At least that's what I've seen in Dallas and Austin.
The deep footings help to divert water around. Especially irrigation.

_________
 

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Discussion Starter #9
We are planning on putting a 12" x 48" wide pillars ..three on each side to keep the slab drifting.
 

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In my experience we usually have to "undercut" the site. Meaning we dig until we get all vegetation out, and get a suitable soil. Sometimes we punch #3 into the ground and then fill with either compacted #2a or #2b limestone. Usually we just lay fabric and fill with 2B and the the top 8" is 2A. Makes for a great base to pour on.
 
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