Mixing gyp-dirt

[handtpipeline]

Ok, my background is in pipeline/utility line work. Over the years, we have also moved a fair amount of dirt. Built ponds, put in roads for sub divisions, house and building pads, etc...

Right now, we are working on a dam for a city resevoir (lake, I know I didn't spell that right...) Anyway, they did away with the earthen spillways on each end of the dam, we cut down about 350' long area in the middle of the dam, and they lined it with Roller Compacted Concrete. Now, we are filling on both ends of the dam, building the slopes and such. The basic fill work is not a problem for us, just loading out of a stockpile, moving, spreading, discing, watering and compacting... No big deal..

The big deal is, the top 5' of fill is gyp-dirt. We have to mix gypsum with the dirt. And nobody here, from us to the general contractor to the federal inspectors have ever been around this... Our first problem is delivery of the gypsum. We are working in south eastern Oklahoma, and the gypsum comes from western Oklahoma. They can only bring us as much as we can use in a day... Second problem, is mixing. Most of the slope is too steep to mix it in place, so we are going to have to mix it in a relatively flat spot, the transport and place it after it's mixed. Third problem is how to mix in the correct proportion... The spec calls for 3 pounds of gypsum per cubic foot of dirt. The mixing spec is to put down 4 1/2" of dirt, a layer of gypsum, another 4 1/2" of dirt, another layer of gypsum, then mixing it with a disc. How can we accurately measure the amount of gypsum and evenly spread it???

ANY ideas would be much appreciated... For equipment, we have our PC200 excavator, a 30 ton Terex arctic truck, a 550g John Deere dozer, a 750J John Deere dozer, Rome disc, large sheepsfoot roller, trench roller and water truck. We are bringing a D9 in to pull the disc, because the 750 won't pull it up the slope. Plenty of power, not enough weight... If we need to get something else to spread the gypsum we will. Just don't know what to get. We've got about 40,000 CY of this stuff to mix up they say.

 

[speedy]

Maybe there is one of these in your area - contact the manufacturer or a dealer.

http://www.stoltzspreaders.com/

 

[heavylift]

this is what we use to mix additives into the soil.
They deliver the product to the area we are working, we then spread the product with a blade, then bring in the recycler and water truck. Then compact the material


http://www.he-equipment.com/images/NewVehicles/2013/NV325607_0.jpg

 

[d9gdon]

Ok, my background is in pipeline/utility line work. Over the years, we have also moved a fair amount of dirt. Built ponds, put in roads for sub divisions, house and building pads, etc...

Right now, we are working on a dam for a city resevoir (lake, I know I didn't spell that right...) Anyway, they did away with the earthen spillways on each end of the dam, we cut down about 350' long area in the middle of the dam, and they lined it with Roller Compacted Concrete. Now, we are filling on both ends of the dam, building the slopes and such. The basic fill work is not a problem for us, just loading out of a stockpile, moving, spreading, discing, watering and compacting... No big deal..

The big deal is, the top 5' of fill is gyp-dirt. We have to mix gypsum with the dirt. And nobody here, from us to the general contractor to the federal inspectors have ever been around this... Our first problem is delivery of the gypsum. We are working in south eastern Oklahoma, and the gypsum comes from western Oklahoma. They can only bring us as much as we can use in a day... Second problem, is mixing. Most of the slope is too steep to mix it in place, so we are going to have to mix it in a relatively flat spot, the transport and place it after it's mixed. Third problem is how to mix in the correct proportion... The spec calls for 3 pounds of gypsum per cubic foot of dirt. The mixing spec is to put down 4 1/2" of dirt, a layer of gypsum, another 4 1/2" of dirt, another layer of gypsum, then mixing it with a disc. How can we accurately measure the amount of gypsum and evenly spread it???

ANY ideas would be much appreciated... For equipment, we have our PC200 excavator, a 30 ton Terex arctic truck, a 550g John Deere dozer, a 750J John Deere dozer, Rome disc, large sheepsfoot roller, trench roller and water truck. We are bringing a D9 in to pull the disc, because the 750 won't pull it up the slope. Plenty of power, not enough weight... If we need to get something else to spread the gypsum we will. Just don't know what to get. We've got about 40,000 CY of this stuff to mix up they say.

I've done this once before with lime stabilization on a conservation dam. I'm not an expert on it cause I'm used to rocky stuff in my area, and I wasn't the lead on this job. This is what I've picked up.

First thing to do is to get with your supplier of gypsum as they have technical people who can be a great resource for mixing strategies, end product soil testing, optimum moisture, and so on. They don't mind helping since it'll only sell more product in the future since you'll be a new customer. You'll also need to coordinate the optimum size loads that they deliver. We had to cut them back to 21 tons instead of 25 or 26 because our mixing area was so soft. We still got the full load freight rate per ton though, so no added costs there. You'll have a learning curve on how much you can process per day so start with one truck on the first day. They may send a rep out to see your project and give you some guidance on how best to stage your operations. Again, use them for all they're worth. They've seen most every type of project already.

Next, it sounds to me like you need a "mixing area". This'll be on relatively flat ground where you can process the gyp dirt. I'd definitely get with the Engineer to see if you could modify the way it's mixed. To get 3 pounds of gypsum per cubic foot of mix, you'll need to know what your fill dirt weighs per cubic foot. I think our heavy black gumbo weighed 105 lbs./cu. ft. To get the right results, you'll need to incorporate this weight and the actual weight of the gypsum per cubic foot into your soil testing proof results. What I'm saying is if your dirt weighs 105 lbs/cu ft, then you're not adding 3 lbs of gypsum to that to get 108 lb/cu ft material. That 3 lbs will be incorporated into the mixed dirt, so since gypsum weighs about 70 lbs/cu ft(according to the internet, check with your supplier) then the mixed dirt will weigh less per cu ft than your fill dirt. Maybe you'll sub this to a soil testing company, but we did it ourselves. IIRC, when using lime it knocked our cu ft weight down into the 88 lb/cu ft range.

Also, you'll need to know what mixing depth you're gonna use. For instance, if you have a 50,000 lb load of gypsum and you want 3 lb/cu ft then you'll need to mix it in 16667 cu ft of fill(50,000/3). If you're using a 1 ft mixing depth then that's 16667 sq ft of mixing area. A 9" working depth will make a bigger area(22223 sf) to get your 16667 cu ft(22223 x 9"). Since we wanted a long stretch so we could use scrapers to pick it up after it's mixed, we would mark off an area like 500' long x 33.5' wide. Then you would place your fill dirt to be mixed at a depth of 1 foot(or go ahead and put the entire 40,000 cu yds down in a big mixing area and only mix one foot depths at a time. For example, 500' x 670' area). Get this area flat enough to roll a marble across it, then unload the quick lime(gypsum) in this area spreading it the best you can as you dump out of the bottom of the pneumatic trailers and then spread it out evenly with a motor grader. If gypsum weighs 70 lbs/cu ft then that 50,000 lb load is 714 cu ft. That makes the depth of the gypsum over this mixing area a little over 1/2" thick(714 cu ft/16750 sq ft = 0.512 inches).

This is where you need to get with the Engineer. The way we did it was to incorporate it with a Rome plow with 36" discs. Instead of that 9 to pull it, I'd go with a Challenger rubber track tractor or very big 4WD tractor. You want to pull it about 5-6 mph, it just works better. We'd set the aggressiveness of the plow to achieve a one foot working depth. You can bury colored survey tape at one foot depths across the mixing area to see if you're getting the right depth. We then hit it with the required amount of water to reach a little above optimum, depending on ambient temps. Then we used a Bomag soil stabilizer to actually achieve the final mix, setting it at a working depth of 1 foot. That quick lime turned the Silly Putty clay into some of the nicest working loamy looking mix you've ever seen. We could self load with 621B's. Once you get it mixed, transport and place it where you want on the dam.

I probably didn't make everything clear, but it's not that hard to do. I couldn't figure out why you are getting a 9 to pull the Rome plow if you can't mix it on the slope. I guess that your 5' of fill is the top 5' of your dam?

To make everything 1000% easier, use a GPS equipped small dozer on your slopes.

 

[mitch504]

Not that this has any relevance here, but:

Lime = Calcium Carbonate (calcitic lime) or Calcium carbonate and Magnesium Carbonate (dolomitic lime or dolomite0
Quick Lime = Calcium Oxide
Gypsum = Calcium Sulphate

 

[Turbo21835]

40,000 cyds is quite a bit of material. Surprised this isnt being done with a pugmill. That being said, you can achieve the same result with a stabilizer as others have noted here.

 

[handtpipeline]

The main reason for the 9, is we have it available. That plus we have to disc the previous layer before applying the next lift, so we do have to disc the slope. This job was supposed to be done LAST December, and we just moved in on it about the 15th of December... And pretty much inherited a mess. We're the 4th dirt crew (so we've been told), and the only ones so far that had any kind of clue what we're doing. The previous crew thought the slope was too steep to work an excavator on it. Which they had a 318 cat with narrow undercarriage. My PC200-8LC didn't have a bit of trouble, although several people on the site commented that they could tell I have a lot more experience than the previous people. The excavator is our only piece of equipment on the job, the rest belongs to the guy we're doing the job for. The previous crew left the 750 hooked to the disc, and tried to hog dirt with the 550g if that tells you anything... The superintendant on the job commented that we moved more dirt in the first 2 days we were there than the previous crew could in 2 weeks...

 

[d9gdon]

Obviously a NRCS job. They love to see contractors fail and even word their specs vague to make it happen.

You still didn't answer my other questions...is it a cap or a total fill of the top 5'?