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Gravel Roadbed Compaction - 1955 Measurement Methods

03/30/2009 5:22 AM

What is the most reliable method to determine roadbed compaction without the use of the latest technology? I guess another way to put it would be, "How was compaction determined by a road builder in 1955? The reason for the question is that I am starting a road improvement project and will be working with marginal inspectors that will have virtually no test equipment on the jobsite.

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#1

Re: 1955 Gravel Roadbed Compaction

03/30/2009 5:57 AM

You will need a lot of laborers for this one. 1955 road builders use prisoners for free laborers. Imagine the slaves in building the pyramid.

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#2

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/30/2009 12:04 PM

They still used the Sand Cone Method for road beds even 50 years ago. The sand cone method is the standard against which all other testing methods are calibrated. However, this is a very time consuming, labor intensive, and user-sensitive test method. It is very easy to mess up performing a sand cone test, and get compaction values that are too high or too low. By far the least user-sensitive, easier to use, faster, and highest precision method is nuclear guage testing, it is really only sensitive to the material being tested within the field between the probe tip and the sensors. It is really up to the geotechnical inspectors to provide the equipment to perform the testing adequately, as their geotechnical or civil engineer (specialized in geotechnical testing) will be responsible for stamping the testing results and submitting them to the local jurisdiction.

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#3
In reply to #2

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/30/2009 4:21 PM

"It (the sand cone test) is very time consuming, labaor intensive, and user-sensitive test method. it is very easy to mess up performing a sand cone test" This is what I am trying to avoid. The travel to and from the lab and the documentation chain with translators becomes very time comsuming. I thought about buying a couple of nuclear gauge testers but am concerned about the training required to operate them.

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#4
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/30/2009 4:48 PM

The sand cone test is done in the field. The compaction curves are run in the controlled environment of the lab, and these are only done infrequently. Compaction testing is always done in the field, even nuclear testing is completely done in the field. Also, you could do compaction curves in a field lab since it just requires a small oven to get to 205 f and the hand held tools. You would not get as good of results and would need to run compaction curves more frequently. It would also still take at least 2 days to get turn around, as you must oven dry samples for 24 hours, then crush and and screen them, before running the curves, then moisture condition, run curves, and oven dry samples used in the curves to get the optimum moisture. There is an ASTM microwave method to oven drying, but the soil grains tend to explode and pop out some what, stick to the covers and such. You must always have a chain of custody for samples, this is not the time consuming part, and you can overnight samples. so you get better results on a compaction curve with a 3 d turn around, or do in a field lab with a 2.3 d turn around. The fastest, easiest, most idiot proofed method for compaction testing is a modern nuclear guage method, as the guage logs the test results and can dump those results for reporting. The operator just has to name the tests and imput the curves to use for comparison. Sand cone is the cheapest compaction testing method for equipment but will give questionable results, limited number of results and cost more in labor (plus it will give you a very pissed of field inspector, so he wont be amenable to discussion solutions to your failure to conform to compaction requirements).

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#20
In reply to #3

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/06/2009 7:09 PM

Oh BTW the training for Nuclear Gauge operators is a one day course. Plus you must be licensed to store them at your facility. This doesn't cost too much if you use them, and is relatively easy to obtain, just takes time for license application processing.

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#5

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/30/2009 11:36 PM

Roadbuilding is not my field, but when we made roads on the farm, we kept running them until the "feet" on the roller were leaving craters less than about 0.25 inches deep. I suppose that indicated that the roller had done as much as it could for the given material.

We could not measure and tell "how compacted" the outcome was, just that the end result was as good as the equipment was able to produce.

(By the way, we used a 1955 Fordson tractor as the major piece of equipment for the roads if that's any help.)

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#6

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 8:40 AM

If you prepare your subgrade properly, i.e. with moisture-conditioning and compactive effort, you can evaluate it with the use of a loaded dump truck as a proof roller. As long as the tires leave little or no impression and there is no visible cracking or deflection of the surface as the tires pass over, you have a suitably compacted subgrade. I would stress the use of adequate amounts of water to insure that the material being compacted is near its optimum moisture content.

Once your subgrade is prepared, you can spread your aggregate base to the design depth. Assuming it is a well-graded product with mostly angular-faced aggregate, you can compact it using a vibratory roller at a low speed (2-3 mph). The key to producing a sound and long-lasting aggregate road surface invoilves the use of adequate amounts of water that is uniformly distributed through the material and 3-4 passes of a large vibratory roller operating at a low ground speed. The better modern vibratory rollers have both amplitude and frequency adjustment mechanisms. In your case the frequency should be low to moderate and the amplitude high. Historically, aggregate pavements were often described as 'water-bound Macadam' because they were placed in an almost saturated condition and compacted. With the use of vibratory rollers, this method is even more effective. I have placed many square yards of aggregate pavement using this method, in fact, many times with water being 'squeegeed' ahead of the roller drum during compaction. This method resulted in a virtually impenetrable pavement and one that is easy to maintain over time.

I once performed a lot of site preparation work under the direction of a very experienced and demanding Geotechnical Engineer. The soils in the area were typcially loose, clean sands. His approach for preparation of building and pavement areas was to require the use of a heavy vibratory roller making 15-20 passes over the area in each of two directions, with the roller travelling at no more than 2 mph. He would observe this process carefully and, if he thought the roller operator was travelling too fast, he would throw something at him to get his attention and make him slow down. He never required any field density testing and he never faced a lawsuit for structural failure on any of his projects. In those situations the amplitude was set low and the frequency high.

I hope this helps you.

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#7

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 8:42 AM

In lieu of testing, maybe you can be very specific in the construction methods. You can inspect for adherence to the construction specification. Not the best way, but may be adequate if the soil conditions are consistent. For example, a specified graded material placed at a certain height compacted x number times with a vibratory roller. Basically and construction specification vs. a performance specification.

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#16
In reply to #7

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/03/2009 4:13 PM

along with a performance spec, there should always be a construction specification identifying the materials used, gradations, strength of materials, and various properties

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#8

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 11:58 AM

Hello Vagabond,

Others have given you the correct info regarding the testing, however I suggest that you have the material being placed for the sub base and base inspected and graded. Not all road base materials are equal. Those with too much sand, or pockets of sand will be difficult to compact and ultimately fail to support the finished surface, weather it be shell, oil and stone or asphalt. I only buy these materials from pits certified for materials to be used on state highways. This material will cost a little more, and the haul fee may also be more, but it is a lot less than having to come back and repair areas that fail. Where no shell pit exists the next best solution is to use soil-cement as your road base. Soil-cement was originally known as posi-pack and was patented by Portland Cement Co. It is an excellent base for areas that experience ground freezing.

TooMuchFun

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#9

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 12:00 PM

Having built roads, highways and airports for 10 years I have seen / used the following:

If you lack a nuclear densometer ('nuke'), fabricate a pointed rod out of 1" smooth steel, and a base plate with a hole and weld a collar (with fillets) to guide the rod. The plate should be large enough to stand the rod on its own (or safely be stood upon by an erstwhile assistant) while you hammer the rod into the ground. By the count of the blows you can determine empirically if you've applied sufficient density. The more blows it takes to penetrate the rod to, say, 100mm, the denser your gravel.

Ensure that your subgrade is higher than the surrounding area so that it can sit free of water (ie. have ditches). Proof-roll with a loaded single-axle dump truck or loaded water truck (approx 8 tonne plus vehicle), if the subgrade 'rolls' ie moves under the wheels, then the gravel beds will not survive. The foundation is the critical for durable roads.

For compaction Doogleass posted a good compaction methodology. The most important aspect is water for compaction.

Ensure that water is added while placing and grading the aggregate and before compaction. Once the surface is smooth graded you can begin compaction.

You can determine the optimum compaction method of your gravel by working with your compaction train (rubber tired and steel vibratory rollers) and water truck on a control strip. Apply water and make a number of passes (3-5) over a 200m length - check the penetration with the rod method (or nuke) at three locations. Make another application of water and make more passes, repeat the testing. The rod penetration will become harder to acheive, and then, once the gravel is 'full' (ie. past optimum moisture), the penetration will be easier - this is the 'down' part of your proctor compaction curve.

The count of water application and compaction passes that got you to the hardest density is your compaction methodology for the entire road.

Subsequent lifts of gravel will have a slightly higher density (use the control strip again) than the ones below, and keep the loose lifts around 200mm thick (depending on your compaction equipment) for 20mm minus crushed gravel.

A 'nuke' needs to be calibrated to the gravel you are testing. This method relies on the idea that the proctor principle behind the test can be put to practical use.

There are a lot of nuances to roadbuilding, The control strip comes from the Alberta Goverment Highway spec, which is quite a rigorous spec.

Good Luck!

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#11
In reply to #9

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 4:54 PM

Thank you very much for what I would rate as a GREAT ANSWER! I just knew that there had to be another method of measuring compaction that didn't include the cone test or the nuclear densometer. I'll have the troopers get cracking on the rod and plate. Can you elaborate on the number of strokes to density.

"Just an Engineer" from Australia is also one person who read my question and "got it". I am working with people that have at best a third grade education and labs that can't compete with a high school lab in the EU or the US. My concern is getting an inspector, usually a kid from the States that is wearing body armor and carrying a rifle as his primary duty, shot either by an insurgent or by one of the contractor's cronies just because he is trying to do his job.

I would like to thank all of you for the advice. It has truely been a learning experience for me.

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#12
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 6:22 PM

Thanks for the mention.

That's one of the great things about this site. Everyone seems prepared to help and offer advice from their background and experience.

Often the full range of responses holds more information than the original post wanted, but these files remain available for review at later times by others and the information provided by others may help another person who isn't facing the challenges of your environemnt, and who might have access to that type of equipment.

How to calibrate a hammer stroke? that will be another interesting challenge. How heavy the hammer? Dropped from what height relative to the end of the rod? and so on. I'm sure that the other responders can give advice on how to "calibrate" the hammer strokes, or even if that's necessary.

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#13
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 7:53 PM

Glad to be of help - I will check on correlating blows and get back to you, however . .

As long as you are consistent in the with the blow count, ie 10 blows every time, measure and record the penetration - A five pound sledge on the rod should suffice. And a little experimentation should give you some comfort and confidence.

Calibrating real density to the blow count does need a lab. The density relies on the type and gradation of gravel you are working with, and every source will be different. Density for 20mm crushed minus > 20mm screened minus (angularity versus round). But for the 20mm crush you would be in the 2100 -2200 kg/m3 density range.

By the way this method is a bastard if you have to pound into a straight pit run gravel - the rod gets stopped by the uneven rocks - Best to use the proofroll method.

Usually when you get to 98% density, you can barely pound the rod into the gravel. I had a site dispute with a tester whose nuke kept reading 92-95% even after running his calibrating procedure. I was ready to pave, but the inspector kept my crew going another day on compaction based on the tester results (I loved it when my crew wouldn't use common sense and call me). I came out to site - couldn't even pound a form pin into the gravel - still had to bring out a 3rd party - but I backcharged them for a wasted day and the 3rd party- and got paid.

Stay Safe - Good Luck and thanks for the GA.

and I love your Mark Twain gold quote - I've often used it myself.

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#15
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/03/2009 2:07 PM

Sorry to take so long to get back to you.

As I thought, there isn't a direct density value that the number of blows will give you unless you can correlate with a nuke.

Just be consistent with your effort so that it is repeatable, ie 10 blows from 12", or 10 'free drops' from 18" so different strength is out of it. Your gravel will be at its most dense when you can barely penetrate.

Good Luck! Stay Safe.

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#18
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/06/2009 4:44 PM

Obviously, you must be aware that blow counts on a stake are not accurate in any way as the penetration of a material is dependant upon the moisture content. Undercompacted materials which are compacted on the dry side, a very poor contractor practice to save on moisture conditioning effort, maybe harder to penetrate then denser materials on the wet side of optimum moisture. Plus it represents only those material in a small area immediately underlying the point of the stake, so like a 3/4" diameter circle. One piece of gravel could present substantially higher results if it happened to underly the stake tip. Also, given your professional experience, you must be fully aware that the reason the nuke gauges fail to present accurate compaction rersults is almost never due to the nuke test, but rather due to a change in the materials the compaction curve is meant to represent. In well manufactured homogeneous aggregate base materials these changes should be minimal, except in situations where there was some loss of control, mixing during placement or some other lack of quality control on the materials. In these cases a new bulk sample should be collected and a compaction curve (D1557 or D698) run. However, the loss of quality control at some point between manufacture and placement may become an issue also if the curve changes substantially, which could lead to additional required testing of the material qualities like strength and durability. Usually it is just better to gwet the moisture a little on the high side through out the material evenly, and recompact.

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#19
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/06/2009 7:05 PM

Absolutely! Ideally, you are taking samples from the processing belt, the stockpile, and the workface, running your QA tests per day, per lot, per tonne of material etc. with a properly tested and calibrated nuke.

But that doesn't sound like an option here.

Going back to post #9 - the idea is to run the control strip such that you find the point where you hit over-moisture, so you can establish a repeatable methodology with any product of any quality. Given the local skills, location and the concern about being shot, it is simpliest to ensure that the product is watered prior to shaping, then recording the number of passes of the rolling equipment and watering.

The inspector can ask the workers continue to roll as opposed to 'failing' the work and risk offense. This method won't work very well with an unprocessed material greater than 1" minus, and especially with a pit-run where your rod can be fully stopped by a solid rock.

I've had my own crews try to pass off the 'dry' method as proper, watering after they've shaped and compacted - drives me nuts. But they learned because I'd make them do it again. The surest way to show a crew properly compacted work is to bring them back to the 'dry' work that got submerged after a rain, versus the properly compacted gravel. The properly done work stays just as compacted. If I really needed to drive the point home, I used to make them dig out the sopping loose gravel by hand.

It is definitely easier to let the weather tighten up over-moisure gravel, than to try to get water penetrate through a crust!

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#10

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

03/31/2009 12:41 PM

What many of the readers have not seemed to do is read your message, LOOK AT YOUR LOCATION, and then answer. Bud, I am in the Green Zone and know what you are facing. I have not 1955 technology to deal with but 1855... Or so it seems. I understand your concern and strongly suggest that you use the last option suggested by RJYOU, between the language and attitude differences between the workers you have and the rest of the world, this is a method that they can understand and will comply with. Good luck.

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#17
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Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/04/2009 2:42 AM

Good Bill H.,

If the sand doesn't blow and the birds fly I should be in the Green Zone at the new embassy sometime on the 14th. My cell number for the Baghdad area is 07704434165. Give it a buzz around 17:00 and maybe we can get together at the Off Site Bar (is that the right name) and discuss building roads in a war zone.

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#14

Re: Gravel Roadbed Compaction - 1955 Measurement Methods

04/01/2009 6:58 AM

I suspect that you have silt under your road base.

If this is so, it can be stabilised by lime slurry injection.

You use lime, sand (about 1:3 I think) mixed into pumpable slurry.

A spear point with some holes behind the point is forced 2-3 m into the soil and slowly withdrawn while the slurry is pumped in.

The lime is forced into the minute weak points of the silt and "reacts" with the silt to form a far stronger material. It takes a few months to gain near max strength (slower than using cement) but goes on gaining strength for quite a long time.

The sand helps to expand the mini cracks so the lime can penetrate better.

Injection is usually done on a grid about 2-5m spacing.

This could help if you have poor soil conditions,

If subsoil compacts well and there are not likely to be water logging problems this method would probably only give marginal improvement, but if you have unstable or soggy subsoil, or a water table which can be high for part of the year, lime slurry injection can give excellent results.

It also has the advantage that you can set the gear up so it can be used from inside a truck, or even armored vehicle, so workers are not exposed to snipers etc.

I'm not sure if this will be applicable to any of your work, but google "lime slurry injection" for more info.

Of course the previously described methods would be used for compaction of the layers on top, but this can significantly strengthen the subsoil underneath and give a far longer life to the pavement.

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