# Moisture Conditioned Pads



## Dirtguy (Dec 17, 2006)

Is this done on a regular basis anywhere else in the country?

We are lucky here in San Antonio to have a large limestone formation (Edwards escarpment) at the foothills of the Texas hill county that gravel is quarried from to produce concrete and asphalt aggregates, road base and many other stone and associated byproducts here locally. We have been spoiled over the years by the cheap cost of crushed limestone. Much of the materials manufactured here are shipped by rail to Houston, Dallas and other areas in the south. However, here recently we have been experience a construction boom and material prices have increased substantially due to supply and demand. This has created a need for other means and techniques for constructing building pads which have most always been constructed of crushed or naturally occurring (pit-run) gravels.

Method:
Rather than installing a gravel pad in compacted lifts, the Geo-technical Engineers are having us preswell the existing soils with water to some predetermined depth to a achieve a potential for vertical rise of less than 1". The existing soil is removed, for example, 5 feet below bottom of slab and then reinstalled to +5% to +10% of optimum moisture and compacted to +90% density in 6" compacted lifts. This can be a pretty muddy situation considering the optimum moisture of many of these clayey materials is about 17% to 20% and we have to achieve at least 5% above that (approaching snot). One of the Engineers insists we mix the mud with a pulverizer/mixer to insure complete amalgamation of soil and solution. I can't even begin to tell you what a quagmire that is, the mixer won't even pull itself through the mud under it's own power, we have to pull it with a D6.

Anyway, just wondering if any others are doing this procedure.


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## jmic (Dec 10, 2005)

Dirtguy said:


> Is this done on a regular basis anywhere else in the country?
> 
> We are lucky here in San Antonio to have a large limestone formation (Edwards escarpment) at the foothills of the Texas hill county that gravel is quarried from to produce concrete and asphalt aggregates, road base and many other stone and associated byproducts here locally. We have been spoiled over the years by the cheap cost of crushed limestone. Much of the materials manufactured here are shipped by rail to Houston, Dallas and other areas in the south. However, here recently we have been experience a construction boom and material prices have increased substantially due to supply and demand. This has created a need for other means and techniques for constructing building pads which have most always been constructed of crushed or naturally occurring (pit-run) gravels.
> 
> ...


Thank the Lord No!:no: :laughing:


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## denick (Feb 13, 2006)

Gee Joe's never been so right with so few words!


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## Dirtguy (Dec 17, 2006)

To add to the problem the pads are typically warehouses around 200,000 to 150,000 square feet.


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## concretemasonry (Dec 1, 2006)

I guess we can scratch Texas off as one of the possible locations for the Garden of Eden.

Dick


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## denick (Feb 13, 2006)

Gee, When will the video be out?


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## Dirtguy (Dec 17, 2006)

It's a horror flick, we're editing right now.


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## rino1494 (Jan 31, 2006)

So, are you telling me that you are not using crushed stone for under slabs ??

I don't see the benefit to saturating the soil above it's optmium moisture content and then compacting.


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## Dirtguy (Dec 17, 2006)

The "theory" by the Engineer is the that we are preswelling the soil by saturating it to the point that it will not swell anymore. For constructability purposes a 12" layer of gravel is used to cap the moisture conditioned soil. This allows the concrete contractor to have a workable surface to pour the slab. Here's a pic of a pad about 40% complete.


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## denick (Feb 13, 2006)

I don't want to sound ignorant but what happens when it shrinks?


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## jmic (Dec 10, 2005)

Dirtguy said:


> The "theory" by the Engineer is the that we are preswelling the soil by saturating it to the point that it will not swell anymore. For constructability purposes a 12" layer of gravel is used to cap the moisture conditioned soil. This allows the concrete contractor to have a workable surface to pour the slab. Here's a pic of a pad about 40% complete.


Gee I thought that was an airport.


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## Dirtguy (Dec 17, 2006)

Well I asked that same question. There is a +/- 8' deep trench that is dug around the perimeter of the pad and poly is installed along the inside wall of the trench and over the pad. The trench is then backfilled before concrete is installed. This creates a moisture barrier around and over the pad that is suppose to keep the moisture trapped in the pad and keep it from drying.

The whole process is a real pain in the a%#, but it is still cheaper than importing 30,000 in place yards of select fill and hauling off 20,000 of fat clay. Given my preference, I would much rather install the select fill. I can set up 20 trailers and have the pad installed in about 60% of the time it takes us to perform this process. But to import the select fill would cost about $12/CY and to export is about $7/CY (all in place CY). That's about $500,000 worth of import and export that is not needed, and man I can move alot of dirt with just labor and equipment for that kind of money.


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## jmic (Dec 10, 2005)

Nick,
I guess it true what they say about Texas. Everything is bigger out there!:w00t:


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## denick (Feb 13, 2006)

The Headaches Too?


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## Dirtguy (Dec 17, 2006)

10-4


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## denick (Feb 13, 2006)

Dirt,

How long have they been using this type of soil preperation?


You didn't just make it up did you. We really can't see much in that picture?


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## tgeb (Feb 9, 2006)

WOW... 

I am glad we don't have too much expansive clay around here!

I see some know and then, but very rarely.

Maybe you should have stopped by sooner, there was guy selling clay, or trying to, to the Corp. of Engineers, to import down to the levees in New Orleans, back in the spring I think.

Do you all remember that guy, he was gonna dig up the family farm or something, wanted to know how much to charge for the clay? :blink:

But Back on topic, DirtGuy you have a heck of a project on your hands, good luck in that mess. It must drive ya nuts to get to work in the AM to a nice dry site then turn the water on and make a huge muddy mess!:w00t:


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## Dirtguy (Dec 17, 2006)

No, I'm a contractor not and engineer. Tell me what to build and I will find a way to bid it, build it and bill it.... and hopefully collect it. 

The moisture conditioning is a fairly new process in these parts. Howe er, we are starting to see it more often. 

We have a 600,000 SF pad that bids in a couple of weeks and it's specified to recieve 60" of select fill. Due to the cost of importing 120,000 CY I would not be suprised to see the owner's engineer request an alternate price to provide a moisture conditioned pad.


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## PipeGuy (Oct 8, 2004)

Dirtguy said:


> ...This creates a moisture barrier around and over the pad that is suppose to keep the moisture trapped in the pad and keep it from drying.


Why can't a moisture barrier be used to stabilze the expansive soil in its in-situ state; that is by precluding both absorption and evaporation instead of just evaporation (after the soil's been moisture conditioned)? At first glance I'd think it much more practical to protect the soil from 'wetting' over time than to preclude it from drying.


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## Dirtguy (Dec 17, 2006)

That is a good point. Like I said I'm the contractor, not the engineer. I guess the reason is that they (the engineer) know that by performing this process there is good consistency of moisture and compacting through out the entire pad of a predetermined thickness.

There are also contractors that do a process of injection that is suppose to achieve the same result, but they have had problems with consistency. If while injecting and the water finds a sand seam it will follow the path of least resistance leaving a large portion of the clay untreated.

The injection method was specified for the stabilization of the ground under the SBC Center (where the Spurs play). After we excavated the hole a contractor from Dallas came down and started injecting using a "snake-oil" concoction of potassium and lignite. Don't ask me why they chose to use that, I can't tell you. Anyway, they got about 50% complete and we had some serious rain that left about 3 to 4 feet of water in the excavated hole, and that was a big f*%&$# hole! Well, the engineer decided that the water had diluted the solution to a point that the process would not work so they had to redesign the basement floor. Rather than use a slab-on-grade configuration they changed the entire floor to be suspended on carton forms. We got a change order to excavate and additional 14" in the bottom.


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