Gravel compaction

[TurnipTruck]

After 25 years, we moved from 11 cars' worth of storage to a lake house with a single car garage. All of the cars, trucks, unimogs, tractors, and hardware store are now temporarily stuffed in connexes and tents or out in the open, so getting them under roof is a priority.
Towards that end, we hired a guy to dig the three feet of dirt off of the hilltop and replace with four feet of gravel. I erred in not specifying compaction of the gravel in at least one foot lifts. He did run a D5-sized dozer while spreading, but my concrete guy is skeptical that was enough. He did recommend watering the heck out of the build site and running around with the biggest plate compactor I can rent. I can borrow a couple gas-powered water pumps and firehose and run lake water all over.
I plan to have a 40x60 monolithic poured, and the site is gravel for 60' down, then a sand lense at the lake level and gravel for another mile or three after that.
Is this sufficient compaction? I would really prefer not to dig it out and reinstall the gravel in properly compacted lifts. What have you guys done or seen done? Nobody near has a nuclear compaction tester. Is a 1/2 dia sharpened steel spike takes X effort to beat in to the gravel Y distance sufficient to determine?

 

[bczygan]

What kind and spec. does the gravel have?

The sharper and less rounded the better. And having fines helps lock things together.

The best is limestone with fines. It compacts into a concrete like mass. Almost impervious to even water.

http://www.multiquip.com/multiquip/pdfs/Soil_Compaction_Handbook_low_res_0212_DataId_59525_Version_1.pdf

https://www.nh.gov/dot/org/projectdevelopment/highwaydesign/specifications/documents/2010_Division_300.pdf

Bill

 

[machsnell]

your guy is right.

if it were mine i would dig it out to at least 2 foot depth and roll with a large smooth drum. 84" 12 ton.

you only get one shot at a slab.

nuke gauge wont tell you anything deeper than 12" and you can get that to 95 plus percent with a large roller.

dont waste your time with a plate tamper. it will not get anything but the top layer.
i
if the guy with the dozer knew that he suppose to compact it in lifts and all he did was track it in i would tell him to come back and flip the stone to one side and rent a big dirt roller and beat that stone like it owes you money. then put 2 more lifts on and roll each of those.

4 feet is a lot to put in and track in only.

concrete doesnt give at all it cracks.

just saw that you didnt tell him to compact in lifts.

hire him to come back and flip it all to one side and do it right or you will have cracks


water is good for getting stone to tighten up. we use it in the dry season or if stone has dried out. most of the time the stone has 5 to 10 percent moisture in it already which is good. it helps it tighten up.

you shouldnt need to water if moist and you roll it quickly after it is spread. if you play with it because it takes a long time to grade it segregates and dries out.

only water if its all dry but usually only needed on the top layer when grading and you dont need to flood it just enough so it isnt saturated and doesnt dry up within 15 minutes of watering.

 

[ishiboo]

A plate compactor is not going to do anything on four feet of gravel. You'll get compaction of the top 2-3 inches if you're lucky.

Realize that even for a plain road, DOTs require anywhere from 6" to a maximum of 12" for a single lift - and they're running 70-100,000lb machines. On a 12" lift, the 12" immediately below it is going to see mild compaction and nothing below that.

A D5 weighs "a lot" in theory - but it's tracked, which does an awesome job of distributing the load. So you're best bet is it's the regular machine (not the low ground pressure variant) and you get 5.6 PSI. To put that in perspective: an average passenger car is 25-30 psi. A human is 3 times the ground pressure (PSI) of the dozer.

If this is a monoslab, I'd have it done properly. If you're going to pour foundation walls, they'll be below the 4' mark. So the only settling would be the floor and not the building itself.

 

[theoldwizard1]

Lots of water. Time (at least 1 year, 2 or 3 would be better). Biggest road roller you can afford.

Hopefully you spec'd sharp edge gravel like crush limestone/granite. Round edge stone (pea gravel. river gravel) does not "lock" together with compaction. It will just sink into the soil over time.

 

[brownbagg]

you cant test gravel with a nuke, because there no fines, you really cant compact it good for the same reason, it will never get tight, just keep rolling around

 

[machsnell]

Lots of water. Time (at least 1 year, 2 or 3 would be better). Biggest road roller you can afford.

Hopefully you spec'd sharp edge gravel like crush limestone/granite. Round edge stone (pea gravel. river gravel) does not "lock" together with compaction. It will just sink into the soil over time.

There is an optimum moisture Content to stone to achieve maximum density based on gradation and specific gravity of aggregates.

Usually this is between 4 and 7 percent.

Loose stone will soak it up and you will be doing yourself more harm than good if you put too much water on it.

Moist not saturated. Especially when doing lifts. You don't want to lock in a moisture level that is too high because it won't evaporate and will cause you to not get density on successive layers.

Like I said unless your stone is dry just water top layer once you habe your lifts done to help with segregation and to achieve maximum density. That way if you put too much water on it will be able to dry up and evaporate.

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[TurnipTruck]

This was all "pit run", which looks like grey/brown fines and stones up to large potato size. No crushed rock, no limestone within a thousand miles. Typically, the gravel in this area drains well enough it will not puddle even in a torrential rain. Humidity varies from 25-35% in the winter to maybe 65% during a wet Fall.
I can't do much for the next five months until Winter is over except worry and plan.

 

[theoldwizard1]

Moist not saturated. Especially when doing lifts. You don't want to lock in a moisture level that is too high because it won't evaporate and will cause you to not get density on successive layers.

I don't disagree with you, but remember, the OP did NOT do lifts. Letting it sit for a couple of years will allow "natural" compaction if it does not dry out too much.


Machsnell, what is you thought about adding a 3-4" lift of "crusher run" (mixed fines and gravel) ?

 

[machsnell]

send us a picture of the material you have.

what was the reason 3 feet was cut out and replaced with 4 feet of stone anyway?

was the soil bad?

what kind of building? footings or piers?
if you arent doing anything for 5 months it will have a chance to settle more but that isnt that long. i have heard it take 6 months to a decade as the "rules of thumb" on how long it takes soil to compact on its own. This would vary for stone and probably be on the lower end but not sure.


i would want to spread a thin layer of CR just to be able to grade easier around the potatoe sized stones.

 

[Modoc]

macshnell and ishiboo gave you your best options. there aren't going to be any quick, easy or magic fix's to not compacting that much fill in one lift. In other words your pretty much screwed, if you just run a jumping jack around, pour a slab and not expect it to not just crack but have major heaves that would trip a elephant. site prep using the proper material and compaction are the most import and most over looked steps to the out come of a quality concrete surface.

 

[TommyK]

You can rent an excavator mounted hoe pac which will compact effectively down to about 2 feet or so. You can probably compact that size area in a day. Regrade the area and compact with an 8-10 ton vibratory roller. You can have nuclear density testing performed which will provide results down to about twelve inches or so below grade. If you can achieve consistent results of 95% or above I would say you are good to go.

Alternatively, you might consider having the slab designed for the soil conditions as they exist right now. It may be cheaper to construct an engineered slab than to remediate the compaction problem.

 

[Modoc]

you could also have a geotec do a report on the material that was imported? and see if it is capable of reaching a proctor of 95% and at what moisture content.

 

[myredracer]

Shoulda been plated compacted in preferably 6" lifts, max. 12". Pit run and even sand can make a good base but needs to be properly compacted.

Before digging any of it up or doing anything else with it, the next step I would take is go talk to a structural engineer and see if a monolithic slab can be designed that will "float" on top of the new gravel. An engineer might be able to give you a few different options.

My experience with pit run is that if it gets saturated, with all of the round "marbles" in it, it can get soft. We have a secondary driveway for access to our field and had about 6" of pit run placed on it and a dozer, trucks and excavator ran umpteen times over it. When it rains, it still gets soft in areas even just walking on it. Never got around to putting down a granular layer on top. Weeds just love to grow in that stuff too.

 

[Bondo]

I can't do much for the next five months until Winter is over except worry and plan.

Ayuh,.... Just the normal freeze/ thaw cycle will settle, 'n compact it more than yer plans of water, 'n plate compactor,....

I agree with the opinions above, that whether a plate tamper, 5 ton roller, or 10 ton roller, yer only compactin' the top few inches,....

That's Why ya fill in lifts,....

I'd wait til Spring, 'n go dig a test hole to see if ya got compaction/ settlement enough to build on it,.....

Never seem yer steel pin compaction test, 'n doubt it'll work,.....
The best field test I've seen is runnin' a plate tamper, or 3 ton roller over the area, 'n hittin' the high vibration button,....

If the roller dances sideways, 'n yer teeth are rattlin',.... she's compacted,.....
but only the top few inches,....

 

[lakeroadster]

Proctor Compaction Test

Why guess?

There are specific tests that can be done that will take all the guess work out of compaction. This is what reputable contractors will do.

https://en.wikipedia.org/wiki/Proctor_compaction_test

Contact a local engineering firm and have them perform a Proctor compaction test to determine if the existing material is compacted enough.

This may require that you provide a 5 gallon bucket of the fill material to the testing lab so they can 1st determine what the proper compaction is. They will then bring the testing equipment out and perform tests on the site.

This testing will cost a couple hundred dollars and is money well spent.

 

[wssix99]

Is this sufficient compaction?

In general, for a slab that you will park cars on - yes. The thicker the slab you put on it, even more so. Heavy trucks on a concrete slab transmit just a few psi to the base below, so compaction is generally not a big deal. (If you were building a roadway with vehicles moving at speed or a foundation for a building - that would be something different, entirely.)

However; you may need to worry about nature's compaction through vibrations. Gravel doesn't settle by gravity and won't compact much from static loads. (Like a D5 sitting on it. BTW - The tracks on the D5 spread out its weight, making it a poor compaction tool. A 100 lb vibrating compactor is many times more effective than a 10 ton dozer.)

Do you get many earthquakes in your area? THAT is what I would be most worried about causing settling of the gravel under your slab.

 

[TurnipTruck]

what was the reason 3 feet was cut out and replaced with 4 feet of stone anyway?

was the soil bad?

what kind of building? footings or piers?.

Three feet of organics and duff and tree roots were removed to get to virgin gravel.

Planning on a thickened edge monolithic slab with a stick-built shop.

 

[Corsair4360]

All of the advise suggesting you talk to a civil / structural engineer are correct. Alaska is an earthquake zone so you need to take that into account as well as the freeze / thaw cycle effects. My first thought would be a "floating" slab, which is used in high shrink / swell clay which is horrible on concrete.

The main thing to take into account is that concrete is strong in compression only. Rebar is there to give it tension strength which is necessary other than in specialized situations. A good engineer can help you alot in your situation, and I would strongly recommend hiring one to help you, it will be money well spent.

 

[Streetbu]

Time is your best, cheapest friend right now. For that much gravel, I would wait 2 years minimum JMO

 

[404]

Rebar in the slab will prevent steps or big cracks. Since you are in Alaska I have no idea how much that would cost.

 

[ishiboo]

Monoslab no way I would do this without having it compacted correctly. If it were a foundation with a separate slab, the worst case would be you would need to have the slab mudjacked or replaced. With everything sitting on the slab, it's pretty critical it stays in essentially one piece.

There are various options for making a floating slab that would work independent of most issues, however they would cost more than simply doing this correctly.

 

[machsnell]

Monoslab no way I would do this without having it compacted correctly. If it were a foundation with a separate slab, the worst case would be you would need to have the slab mudjacked or replaced. With everything sitting on the slab, it's pretty critical it stays in essentially one piece.

There are various options for making a floating slab that would work independent of most issues, however they would cost more than simply doing this correctly.

what he said. no easy answer with some homeowner elbow grease to solve your 4 foot problem.

its only 60 x 40 and all of this can be done in a day and you dont have to wait years or guess or pump a bunch of water. a loader or a dozer and a big roller (BIGGER BETTER HERE) is all you need. a bobcat would be handy if just a dozer. the space is small.

proctor costs 1000 dollars and is a week plus test. not needed. geotech not needed. take that money and get a dirt or asphalt guy with yelllow equipment and do it right.

your slab will float you just dont want your sawcut slab to float unevenly because it will settle and drop and create opening cuts and uneven plane.

we did a pervious area in clean 3/4" stone which is supppose to be "self compacting" which is a loose term it just doesnt settle as bad as mixed stone gradations like what you have. That 2.5' area was put in with a dozer and rolled in one lift. we paved it and with the construction traffic over asphalt it settled 4 inches. we paved it temporarily until construction was done and then installed pervious concrte so it didnt matter.

Point is that 4 feet of your type of stone has a lot left to settle. imagine that for your slab and turndowns. IT HAS to be tight.

chalk it up to learning the way i learned a lot in life - the hard way.

**** it up and pay a guy you trust or your concrete guy who was wise to advise you not to pour on it and get it done.

guy just told me about welders - pay one time cry one time.

 

[lakeroadster]

Trust but Verify.....

Proctor costs 1000 dollars and is a week plus test.

Once the sample is analyzed (about $100) the test can be done on site in less than an hour (another $100).

Everything else is just speculation and trust without verification. That's why important projects always include Proctor compaction tests..... documented verification of compaction.

 

[ishiboo]

Re: Trust but Verify.....

Once the sample is analyzed (about $100) the test can be done on site in less than an hour (another $100).

Everything else is just speculation and trust without verification. That's why important projects always include Proctor compaction tests..... documented verification of compaction.

There was no consistent process used except "spreading the gravel". It would take many tests, both to get down 4' and to cover the area.

No, it just needs to be done correctly.

 

[lakeroadster]

Re: Trust but Verify.....

There was no consistent process used except "spreading the gravel". It would take many tests, both to get down 4' and to cover the area.

No, it just needs to be done correctly.

And verification is needed that is has been done correctly...

 

[ishiboo]

Re: Trust but Verify.....

And verification is needed that is has been done correctly...

Oh, sorry. I thought you were saying to do one test of the current setup... read too fast.

 

[machsnell]

I have never heard of getting max theoretical specific gravity or optimum moisture for 100 bucks on site.

We send out and two samples is 1000 bucks. And it takes time.

Beside the point really. If you are at gravel base and material is decent and you use a big vib roller you will make 6 half passes and I guarantee you will be over 95 percent. Probably higher with that base.

And if it so cheap to get a rice (Marshall) number on it and that is the route then the tech should be there as you are bringing up your lifts taking shots to get a roller pattern but since there is no trust then you would need shots on every lift and that would be more than 100 bucks.

Trust me this is being way over thought.

How many guys here had their dirt proctored and had their backfill tested and their stone compaction tested and just so you know you aren't being screwed on the concrete a slump and cylinders on your concrete for their garage?


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[wssix99]

Monoslab no way I would do this without having it compacted correctly.

what he said. no easy answer with some homeowner elbow grease to solve your 4 foot problem.

+2

You could probably get a monolothic slab engineered so that it can withstand some good movement and the development of voids underneath, but the cost of designing and building that would very likely dwarf the cost of getting some heavy equipment back out to your site to move the gravel around and properly compact it.

 

[lakeroadster]

I have never heard of getting max theoretical specific gravity or optimum moisture for 100 bucks on site.

We send out and two samples is 1000 bucks. And it takes time.

Beside the point really. If you are at gravel base and material is decent and you use a big vib roller you will make 6 half passes and I guarantee you will be over 95 percent. Probably higher with that base.

And if it so cheap to get a rice (Marshall) number on it and that is the route then the tech should be there as you are bringing up your lifts taking shots to get a roller pattern but since there is no trust then you would need shots on every lift and that would be more than 100 bucks.

Trust me this is being way over thought.

How many guys here had their dirt proctored and had their backfill tested and their stone compaction tested and just so you know you aren't being screwed on the concrete a slump and cylinders on your concrete for their garage?

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Local engineering place, $60.00/hr, on site Proctor tests... even if it is $1,000 how much re-work will that pay for?

You're a contractor, right? Would you be willing to back up your comments, meaning, I pay for all the testing, if it fails, you pay to re-work everything, including testing charges?

And then if the concrete cracks and fails (we agree ahead of time on what fails means) within lets say 5 years, you pay to have it removed and replaced?

It isn't a trust thing, it's a verification thing. You say "trust me" or "I guarantee", I say great, let's verify it.

Surely you don't have an issue with verifying what you are so sure about, when you are working on my dollar... right?

 

[machsnell]

Local engineering place, $60.00/hr, on site Proctor tests... even if it is $1,000 how much re-work will that pay for?

You're a contractor, right? Would you be willing to back up your comments, meaning, I pay for all the testing, if it fails, you pay to re-work everything, including testing charges?

And then if the concrete cracks and fails (we agree ahead of time on what fails means) within lets say 5 years, you pay to have it removed and replaced?

It isn't a trust thing, it's a verification thing. You say "trust me" or "I guarantee", I say great, let's verify it.

Surely you don't have an issue with verifying what you are so sure about, when you are working on my dollar... right?

You can spend your money how you want to I am happy to work alongside Geotechs. We do so with many crews everyday on commercial sites.

Most homeowners don't have the spare funds to spend on this type of testing. It is a SLAB on grade we are trying to guide him how to minimize cracking along his cj's not support a ten story building.

OP if you have an extra 2 g's to spend on getting proctors and compaction tests listen to him and your stone will be verified to be brought up to grade and you will know that it is. You can test your concrete for another 1500 and get slump air and break tests done for your pour.

If you want to go to quick school by someone who has been doing this for 20 years and is more than happy to help you save money from having to go the other route which I have never even heard of a homeowner doing.

Pm me if you would like to talk on email or over the phone I can put it to you plain and simple. I don't have many specialties but this definitely is my specialty and I would be happy to help.

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[coldh2o]

I don't have many specialties but this definitely is my specialty...

Hard to believe, when you suggest theoretical maximum specific density testing for aggregate compaction. This testing is related to asphalt compaction and mix design, and has nothing to do with Proctor testing of aggregates to determine optimal moisture content for compaction.

 

[machsnell]

Hard to believe, when you suggest theoretical maximum specific density testing for aggregate compaction. This testing is related to asphalt compaction and mix design, and has nothing to do with Proctor testing of aggregates to determine optimal moisture content for compaction.

Correct misspoke. Max density. Theoretical max for asphalt design. Brainfart.

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[lakeroadster]

I have never heard of getting max theoretical specific gravity or optimum moisture for 100 bucks on site.

I just had density testing done last Tuesday on the sub-grade prep on my 30' x 44' barn. We used Class 6 fill from a reputable gravel pit that had Proctor Data on file.

Total charge for on site density and moisture, including the mileage and report, was $160.

Spending $160 seems like pennies when compared to the thousands of dollars that will be subsequently spent on concrete and labor?

Trust but verify. Tell your contractor up front that you will pay for the testing, but that if it fails that the contractor will be required to pay for the rework. When the contractor knows you'll be testing, they'll do their due diligence to make sure it is right. And don;t pay them a dime until it is.

I just felt compelled to update this thread with this data... It's not much money, and you'll have the peace of mind knowing the job was done right.

 

[theoldwizard1]

Trust but verify. Tell your contractor up front that you will pay for the testing, but that if it fails that the contractor will be required to pay for the rework. When the contractor knows you'll be testing, they'll do their due diligence to make sure it is right. And don't pay them a dime until it is.

I just felt compelled to update this thread with this data... It's not much money, and you'll have the peace of mind knowing the job was done right.

Thanks for updating ! I will only add, "If it is not in writing, it has not been said." Write your own addendum to the original contract. Include all items that your had verbally discussed (type of gravel, source, method of compaction as well as testing and consequences of failing the test). If they won't sign the addendum, time to start looking for a new contractor.


(I had a clause in a landscape contract about $100/day penalty for not finishing on the agreed upon date. They were late, but I did not enforce the penalty.)

 

[matt_i]

@ lakeroadster: how thick (nominal) and how did they compact it before measurement? Standard walk-behind plate compactor?

 

[lakeroadster]

@ lakeroadster: how thick (nominal) and how did they compact it before measurement? Standard walk-behind plate compactor?

Mini-Excavator with compactor
Jumping Jack
Roller
Plate Compactor

Check out my build thread, start with thread 134, Page 7 ... link in my signature line below.

 

[matt_i]

Mini-Excavator with compactor
Jumping Jack
Roller
Plate Compactor

Damn!

 

[TurnipTruck]

The concrete guy was finally able to walk the thawed gravel pad yesterday, and is recommending two feet of gravel pulled off and compacted in lifts. We are awaiting an estimate from his preferred excavator guy who has a roller compactor.

 

[forAK]

I just spent 4 days and $2000 to do the work myself renting the equipment. I had to go down 14' to dig up an old crib and put it all back in with 12" lifts. You already have the gravel there. Strip it off with an excavator and start rolling, throw more in with the excavator and then roll. Take advantage of this awesome summer we're having. BTW, if you need another bid on the concrete, I can PM you his name. You can even check out the slab he just did for me at an INSANE price!