I’m constructing a 18’x32′ one story addition onto the side of my house. The house is build on a concrete slab and I would like to pour a slab for the addition as well. The addition will require about 18″ to 20″ of compacted material for the pad. I have access to a 34hp Kubota tractor with a front end loader. My question, would this tractor be adequate to compact the fill if I layered the fill a few inches at at time or would I need to rent some type of compactor? What do you guys think?
thanks-
Replies
Not more then 6" of loose soil at a time, and use a proper tamper.
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Although the tractor is heavy, its not "really" a packer. It might work but not as good as a vibratory packer or such.
I'd rent one and do it the best way as they are like $50. a day.
Just my .02 cents of course
Put a load in the bucket and compact with the front wheels. About a 3" lift at a time. I run my tires full of water, it helps.
Even compaction is important so, driving north and south, working from left to right, keep the left tire next to the previous track. When it gets to the area compacted by the right tire, shift to new ground.
Then, drive east and west so you get a cross pattern. When a hard baseball or golf ball bounces nicely, do the next lift.
SamT
Dude, you're busted. On the last thread like this you made the point that most equipment has low ground weight and doesn't compact fill well. It's still true. As someone else said, for $50 you can rent a plate compactor. There is a world of difference. I did quite a bit of compacting recently after my excavator drove his mini around inside the foundation spreading gravel. While his machine is not large it probably does weigh 8 or 10 tons. Sounds like a lot of weight but the 200lb Bomag plate I used did a helluva lot better. I have another slab prep going on right now and have actually been parking my truck on the fill for several days, coming and going. It does damn near nothing to compact the gravel.
"Dude, you're busted. On the last thread like this you made the point that most equipment has low ground weight" You need to go back and reread that thread. I specifically addressed using a crawler. This guy is using a wheeled tractor. The crawler was used to compact 1 18" lift. I told this guy to use 3" lifts and how to test it. I know this works, but it is not time efficient. And time is spelled $$$$$.A crawler gently lays 5-7 psi down on the soil, a wheeled tractor with a full bucket is gonna put around 50 psi ROLLING load on it.It's a whole diff'rnt ballgame.BTW, your friends mini, might way 2 - 4 tons, and it's tracked, a crawler.SamT
Edited 9/17/2007 11:00 pm by SamT
jumping jack
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Haga su trabajo de fricken
No amount of driving will work. If it did, contractors would do it and inspectors' measurement instruments would show it was sufficiently compacted.
The only technique is vibratory compaction, and for small areas a jumping jack works the best. Plate type compactors don't work on stone base.
>>Plate type compactors don't work on stone base.
That sure isn't true of the crushed rock we fill with here. I see jumping jacks used occasionally but it's generally in ditches where a plate would be hard to get around, or too large.
"Plate type compactors don't work on stone base."
What a ridiculous statement! I have installed literally acres of paving stones over the last 20+ years. We have always used plate tampers. The key is to do small lifts, and tamp each lift.
Jumping jacks compact well, but do not leave as smoothe a surface, which is perhaps more important with pavers than concrete. But to say a plate tamper won't work on stone base material is absurd.Bear
from the standpoint of running density test on compacted aggregate. plate tamps do not work, they just make it look pretty.Haga su trabajo de fricken
I'm gonna put a fair amount of effort into this reply so I hope it doesn't fall on deaf ears.
The most expensive thing you can do is skimp on site prep. It's the cheapest part of the job (dirt cheap) if you do it right, and the most costly if you have to go back anbd fix it later, especially if you have a structural failure.
The short answer to your question is "probably not".
With a certain amount of experience and skill and on particular soil types it is conceivable that you could achieve an adequate degree of compaction by wheel rolling it, but we don't know what kind of dirt you're dealing with and the fact that youre asking this question tells me you probably don't have the experience.
That's OK -- you'd die laughing if you saw me doing finish carpentry.
The purpose of compaction is to achieve a predictable and adequate degree of bearing competence. That is in some part a function of the soil type; assuming suitable soil, that degree of compaction is expressed as a percentage of maximum theoretical density.
Hang onto that concept of density, it's important. Soil can be hard and still not be densified.
That theoretical maxium density (which is not the true maximum density) is typically indexed to a test called a Standard Proctor. It will be an expresion of how many pounds per cubic foot your soil will weigh at that theoretical level of compaction.
This test is really a matter of dropping a specific weight from a specific height a specific number of times on a certain sized sample that is at the optimal moisture content. The particulars are unimportant. If you were building a bridge or a power plant we'd use a Modified Proctor, which is mostly about hitting the sample harder.
So the max density Standard is not the same as max density Modified.
Why is this important?
How compacted is compacted?
Code is 90% of a Standard Proctor in most jurisdictions, most architects will call for 95% mostly because they are worried about covering their butts, however I have no problem with that. 95% is good to shoot for.
Undisturbed soil can run right around 88% to 90% but not always.
The scale is not linear -- 95% takes a lot more work to achieve than 90%.
And most importantly, the moisture content needs to be right -- that is, within about 3 points of optimal.
If the moisture content is not pretty close you're wasting your time.
Fortunately, this is fairly easy to determine without geotechnical engineering. If you have very sandy or very clayey soils (poorly graded) this doesn't work so well, but generally, if you wet the soil to the point where it will form a ball, squeeze it really hard and your palm should not be wet at all. Now drop the ball on a hard surface from shoulder height. If it splats it's too wet, if it falls all to pieces it's too dry, if it cracks in two or three big chunks, it's about right.
Now, what to hit it with?
They make all those different pieces of compaction equipment for a reason. And Brownbagg is of course right, those little 180 lb. plate tampers are for making asphalt patches pretty. Keep 'em away from the dirt, they're useless.
Short version -- the more granular a soil it is, the more it wants to be "vibrated" into place; that is, high frequency, low amplitude. This is your very large (880 pound) reversible plate or your vibratory smooth drum roller.
The more cohesive a soil it is (the more it sticks to itself) the more it wants to be "rammed" or "kneaded", that is, low frequency, high amplitude. This is your padfoot roller, sheepsfoot roller, jumping jack, and in some cases, a rubber-tire roller.
In the hands of a skilled operator, yes, a dump truck, loader, etc.
It's critically important that you do not over-wet the soil, if it starts acting even a lttle bit like jello ("pumping"), dig it up, dry it out, do it again.
Equally important that you don't overwork it -- once you hit density, stop. If you overcompact it you can shatter the subgrade and it will be far less compacted than when you started.
If you have a choice, you want to use soil that is well graded ( a good mixture of coarse to fine particles) and not too plastic. High plasticity can be trouble, both for expansivity and shear failure.
Gradation test: Take a handfull of dirt, put it in a glass jar 3/4 full of water and shake it. The sand settles out within seconds, the silt settles out in a few minutes, the clay can take hours.
Plasticity test: Now take a sample about the size of a golf ball, wet it, take a little bit and try to roll it out like a potter might roll clay out for a coil. If the resulting "worm" gets pretty long and less than about 1/8" in diameter before it breaks, you might have problem soils.
Work in lifts no more than 8 inches, blend the soil well to optimal moisture content, and take your time. As previously recommended, cross-rolling is often helpful.
I probably just screwed myself out of a magazine article here. <G>
Cat,
Lest you think that no one is listening;... much obliged for the edification.
Although the sensitivity to sounds above 15KHZ is just about shot now, I do still listen from time to time with what I've still got left.
Thanks,
STAINLESS
<<Although the sensitivity to sounds above 15KHZ is just about shot now, I do still listen from time to time with what I've still got left.>>Same here -- a few years in Uncle Sam's Animal Farm, a few years on old HDs, and a few years on tractors . . . well, it's earier to read than listen now. <G>Thanks for the good words.
I probably just screwed myself out of a magazine article here. better you than me.98% of all concrete cracking i due to uncompacted subsoil.Haga su trabajo de fricken
<<98% of all concrete cracking i due to uncompacted subsoil>>Why is that concept so difficult to convey?
Why is that concept so difficult to convey?Because the other 2% is concrete driver or concrete finisherwhen concrete leaves the plant, at that time it is perfect, its downhill from that point..Haga su trabajo de fricken
Yes - thanks for the edumication. I've got a couple of slab pours coming up and now I know what to ask for.
Forrest
<<Yes - thanks for the edumication. I've got a couple of slab pours coming up and now I know what to ask for.>>You're welcome. We haven't even gotten to bearing pressures, shear strength, and drainage, so any more questios, fire away.
I've made a document from your two posts that I saved as an instructive Word doc.
Forrest
For those of you who have never worked with a testing lab, here are two typical reports.
One (test2) is for concrete strength with cylinder breaks at 7 and 28 days. As you cann see, it was spec'd as 4000 psi mix, and we got 4350 at 7 days. Slump was only 3.25 inches. This project went really well, good GC, good concrete batch plant.
The other report (test1) is for soil compaction prior to laying asphalt in the parking lot. Somewhere I have a similar report for the under-slab work, but I can't find it. The compaction ranged from 95% to 101% with a new-kleer gauge."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I know Curtis Howe.last time I talk to him he was in Roanke Va..Haga su trabajo de fricken
I don't care what the other boys here say about you, you're pretty sharp."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
My profound thanks for the input from everyone especially catskinner for taking a lot of his time to educate us on soil compaction. I think you have talked me into hiring a contractor for the pad work and I'll stick to framing once the slab is poured. Again thanks to all.
I think you have talked me into hiring a contractor for the pad work
Don't give up too easily. With the right knowledge and a little help and the right tools, you can do it yourself. "Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Thanks to everyone for the good words.'Bagg is of course (again) correct -- the overwhelming percentage of foundation failures is due to inadequate site prep.There are foundation designs that can compensate for bad soil conditions, but it's usually cheaper to do the dirt work right.So to continue in this discussion, since we have some interest, and especially for those with upcoming projects, that glass-jar test and the field plasticity test are a couple of good indications of whether it's time to call for a professional opinion.I forgot to mention two other things on the glass jar test. First, the presence of any organics (dirt that floats) is sure trouble. Secondly, expansive clay is also trouble. Watch for this in the jar. If you suspect expansive clay, investigate right away.Assuming you want to proceed, take a clean representative sample (drywall bucket of dirt) to your local geotech firm. Tell them you want a sieve & PI and a Standard Proctor.The sieve report will give you a way to understand the gradation accurately. The PI (plasticity index) will most importantly tell you how this material might act under load, and most especially its shear strength when it gets wet.Your geotech folks can make some recommendations on the basis of this report.What's Plasticity Index?When you take some dirt and start adding water at some point it will start behaving as a plastic. There are normative criteria for this.That point, expressed as a percentage of water by weight, is the plastic limit.If you add more water, it will at some point (again, quantifiable against normative standards) begin to act as a liquid. That is the liquid limit.The arithmatic difference between the LL and the PL is the PI.At the low end, you have non-plastic material, like sand. The reason 'Bagg is always saying to use sand is because it works very reliably. It will not get hard, but it will get dense. Remember, never confuse the two. Soil compacted hard can still fail.At a PI of about 10 or 12 you've got a fairly cohesive material, easy to work, generally good shear strength. At a PI of about 15 you've got a soil that is somewhat resistant to the movement of liquid water at 100% of a Standard Proctor, but the structural engineers are on the edge of their seat.At a PI of 18 your engineer is thinking about telling you to pull it all out and blend it down with structural fill to a lower PI because if water gets under your house you could have a shear failure.Over about 20, I wouldn't need the engineer to tell me, I'd just do it.OK, so you've got your sieve and PI and your Proctor. In all that info there will be an optimal moisture content and a moisture curve.You want to hit +/- 3 points of optimal, and notice that curve. The steeper it is, the more careful you need to be.So you get a couple lifts in and call for your test. The tech comes out with a nuclear densometer, which measures backscatter and gives you a fairly sorta close reasonable guess as to how dense the soil really is. Geotechs like ND because it's fast and profitable. Contractors like ND because it's fast and fast.Smart architects and engineers worry about ND because it's not terribly accurate. My understanding is ND can have as much as a 4% bias either way. I don't know if that's with all machines, or if it's always true, but I err to the side of caution. So hit the 95% and you know you're to code even with the bias.Big kudos to the architect who supervised the compaction. I get written reports, specifying the absolute elevation (ASL)that we took the test at and where in the project it is taken. We keep these reports on file, and my geotech firm notifies the contractor if we fail a test. That doesn't happen very often. Maybe once every other year if the soils are really weird. If we do, we rip it up and do it over.So for those who can't get out into the field, just get the reports faxed to you before the formwork starts.That, and some practice, is pretty much it. I wouldn't discourage anyone from trying it. As for the OP, you can probably do this just fine. Anyone motivated enough to hang around here and learn is probably more than capable of doing a good job.
ND can have as much as a 4% bias either way.
My machine is 12 %, but I know it and allow for it. I compare with sand cone daily.Another point proctor curve. you have to hit 95 % on that curve so take the max compaction, multiply by .95 and that the lowest you can go, then look at moisture at that point. if you are at ten % on the curve and you trying to compact at 18 % or 5% you aint going do it, you wasting your time. so if you have 40 dump truck running at 5% moisture, you are throwing money away. get the moisture within 2% of the curve..Haga su trabajo de fricken
You're most welcome. I think on the balance I have still learned far more around here than I have ever paid y'all back for.<<I think you have talked me into hiring a contractor for the pad work and I'll stick to framing once the slab is poured.>>I'd think you can do this yourself with some rented equipment if it's available. If you're careful and want to do a good job you are already ahead of the contractors I see out there with bleeding to death backhoes, no knowledge, and bad attitudes.
Cat, quick note. Well said!!! Should be required reading, magazine or otherwise! Most homeowners or owners in general don't understand the critical nature of starting a building on the best foundation possible and that's not the concrete that goes down in the hole.
Here comes the fun part. As an Architect I do spec a Standard Proctor 95 for bearing and on one occasion have stood over a job and made sure I got it. (Steep hillside, side cut into it, two story with basement built on it, standing for 15years now and no problems).
Why 95? Most of the time I hope to get 90! I can't stand over every job. And that's not to say that every dirt pusher needs to be watched. Generally you guys are the least of my problems.
ciao, ted
Wow, you thoroughly scared me to death. Did clearing and grading and now ready for pad on sandy and clayey soil. You anywhere near Foley AL?:) Thanks for all the info. and expertise!