failing compaction efforts in silty/sandy material

[kurtjfred]

Hi all. Newbie here and first post ever. Working in Southern Cal and getting my ass kicked trying to achieve 95% compaction on some very silty/sandy material in trench backfill. County inspection is using a caltrans wet density test with a nuke gauge and not getting results until following day at soonest. Working deep in some places (almost 20') and having to close up streets at end of each day. Can anyone explain to me with great detail the methods and differences between the dry density and wet density testing methods. Or can you direct me to someplace online that I can get a thorough education on the differences. I would like to learn every possible detail about them, even their history and development. Thanks in advance for any help.

 

[DarthSoilsGuy]

dry density is calculated once you know the wet density and the moisture content in the soil. Any test that is worth doing will give you both. The information should be measured in minutes not days.

i can't see any reason why a 1 day wait is needed. The only exception to this would be that you scheduled the testing needs with them on short notice and they weren't able to run the lab analysis on the fill soils until coming on-site. If this is the case, things will get better. They should be giving you enough information for you to continue filling while on-site, even if it is "preliminary until reviewed by PE".

i did a quick search on google with keywords (soil compaction Proctor) and the 1st link (below) looks like a pretty basic and all-around good starting place.

http://www.concrete-catalog.com/soil_compaction.html

after you learn more about it, feel free to post test results with your questions.

 

[dirtsqueezer]

What is the caltrans wet density test? I'm used to using a modified proctor test, and said nuke gauge. I can give more detail if you're truly not familiar with it.

 

[cvg]

discuss with the inspector and see why the delay and see if there is some reason why they can't give you the results sooner. One possibility is that the field density must be compared to the lab density for the soil. If they don't have lab test results for the soil, then they would have to take a sample back to the lab for the test and that might explain why you don't get an answer till the next day. The pdf below (second link) describes this 2 part testing procedure.

By the way, if you have your own geotech performing QC and you give it sufficient effort to ensure 95% compaction, then why can't you close up the trench and wait for the results? They are for quality assurance anyway and should only be confirming your own results of the quality control testing...

check the following which may give you more information

http://www.dot.ca.gov/hq/esc/ctms/ctmsindex100.html

http://www.dot.ca.gov/hq/esc/ctms/CT216Oct2006.pdf

 

[TDAA]

They may just be getting the wet density from the gauge and taking a small sample to get the moisture under lab conditions. This moisture would be used to get the dry density to compare to the curve (assuming they have that, and that is not what is being waited on as mentioned above).

There could be several reasons for this, including not wanting to mess with a trench correction for the gauge, the soils have a variable mica content (or other minerals) that would make using a moisture correction impractical, or the spec provides the ASTM method for "Laboratory Moisture Content" (as in oven moisture) and they do not feel like bending the rules to allow themselves to burn a sample in the field (using a cook stove).

Someone please correct me if I am wrong, but I do not think there is a wet density method. Everything that I have used is based on the dry. The reason is the wet density accounts for the weight of water and the weight of the soil. There is no way to tell how much of the total is from soil, or from the water, without determining the amount of water. Then you might as well calc the dry density. With experience, you can get some idea of where things are likely to fall based on the wet density, but it is not exact.

Ask the inspector what he is taking the samples for, and if it just the moisture, ask if he could burn one in the field to give you an idea of how your work is going. Unless this is SOP for them, he is holding you up.

Communicate and Document.

 

[Stoph]

I have occasionally seen the Sand Cone called a Wet Density method, but it doesn't sound like this what they are referring to in this case.

 

[msucog]

i'm varying from the question put forth a little, but why not just do drive ring or sand cone density testing and cook the dirt in the field? even if it does spec lab method, someone should see that they should do the field test for the sake of getting the thing backfilled. perform lab test as "confirmatory" testing if someone thinks it's that important. there's enough error (perhaps variance is a better word) in the method itself that i don't see the difference as far as the density and moisture tests. proctors with oversized particles is a different story (should be performed in the lab). as far as nukes, i won't use them on anything with mica (except GAB where the moistures are so low it seems to do fine--do multiple correlations each day though to back up the readings).

by the way, searched wikipedia (even though i don't like it) looking for an in depth explanation of the whole process since it's not a two paragraph type "thing". interesting line at the bottom about wet density testing in california. i'll keep my eyes open for a good site that discusses the caveats of Proctor testing. i'd say a lot of it makes much more sense when you actually perform a the testing yourself (sampling, testing, plotting curves, data anaylsis, trouble shooting why a modified Proctor came up lighter than the standard Proctor on the same material sample, etc) or have the opportunity to review a significant amount of data.

 

[kurtjfred]

Thanks for the input so far guys. I guess I could have offered some more info to make things a little clearer. I am the contractor and the county is the inspection/code enforcement agency/customer. The job specifications spelled out the testing method they would use and it is the CalTrans test 216. The time delay is that they take a sample and pound a curve for that particular sample at each and every locations a test is taken. Hundreds of services laterals coming off tens of thousands of feet of main.
In over 25 years of underground construction, I have always had a soils/geotechnical engineer observing our work and using a dry density test with the curves already having been pounded in the lab. The soil analysis usually is done previously when the initial soils report is done for the project. There are times when you may encounter some soil that they may not have sampled previous and would require a new curve to be found.
What I understand about this caltrans 216 test is that you cannot fail compaction due to moisture. There is not an optimum range given that you must fall in. Most work I have performed has a percentage of compaction and a moisture range that you must be in.
By the way, I am familiar with a sand cone test and this is not being used.

 

[msucog]

here's the wikipedia link

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

"The California Department of Transportation has developed a similar test, California Test 216, which measures the maximum wet density, and controls the compactive effort based on the weight, not the volume, of the test sample. The primary advantage of this test is that maximum density test results are available sooner, as evaporation of the compacted sample is not necessary."

i'm not familiar with this and not sure how it works. i'd be interesting to here the explanation about the theory from someone out west familiar with the method.

 

[oldestguy]

Just one comment:

If you are finding that your work does not pass the precentage compaction and the inspector is using a nuke gage, bring on an outside texting lab using sand cone. More often thatn not, the nuke reads lower than actual. Also, ask that the inspector show his calibtation data for his equipment against known soil density at your site, not some lab calibration. I believe ASTM requires this calibration, but most labs are ignorant about this.

 

[BigH]

Years ago, Ontario developed a site test for determining quickly the percent compaction. You had to take the proctor mould out in the field with you and scales, a special "ruler". You would do a field test via sand cone or rubber balloon and determine the volume of the material removed. You would then take the material and either dry it slightly (if apparently too wet of optimum) or you would add some water to it to bring it to optiumum. The ruler would tell you how many total blows you would need to use for a "Proctor" depending on the volume removed in the hole. Say you are to use 73 blows - then you would compact the material in the mould using 24, 25, 24 blows. You would then determine the volume of the material in the mould (also by the special "ruler") after you have compacted it. Then you compare the "in situ" volume vs the "mould" volume to get % compaction. Of course, your technician needs to be "good" at estimating if something is at or near optimum. This was always a good method - though slow.
What the agency appears to be forcing you to do is riduculous in my view and you should bring this up with the superiors or the agency. Some common sense "heads" must be able to make adjustments - but you need to propose a suitable and acceptable method to them. Sadly, one can argue that you bid the job knowing what the specifications say and that should be included in your price. . . .
You don't really indicate if your compaction is good or not - you are basically questioning the "time" it takes to go through each "round". Do you meet the specs on the "slow boat to China method?" If you do, this is another point to bring up with the agency.
Compaction is such an interesting topic. A topic that every Tom, Dick and Harry seems to think he is an expert in (regardless of training/education background) - yet, it always seems to have the most pages of any real good book of any other topic (see Winterkorn and Fang/Fang).

 

[oldestguy]

Interesting twist there BigH.

Years back I heard a lecture by a US Bureau of Reclamation soils guy, name forgot. He described the Rapid Compaction Control Method, then number E-25, as written in my 1963 version of the "Earth Manual". I see that Vulcan.com has a recent edition of this manual, but no test procedures shown there. It basically involves three compaction runs at differing moisture contents.
Many references in a Google search bring up comments about the "Rapid Method". However, my searching has not found it available in a recent publication. It is estimated to get the result in an hour out on the job.

Some references, such as ASTM papers, refer to USBR7240, but as I view that method, it is mostly how to log field explorations.

I wonder if it is still in use.

 

[BigH]

Not sure - my old copy of the Earth Manual is in deep storage. I wonder how much money is spent trying to get over the hurles of compaction control - what is good AND YOU KNOW IT, but tests come out crappy. On one job, the nuke was giving me 80% compaction (standard proctor MDD) for a coarse graded crushed sand and gravel that had 10 passes of a 15 tonne vibratory roller. Go figure!
Cornell lost to Princeton 34-31 on Friday night.

 

[DarthSoilsGuy]

kurtjfred-
don't push the argument that they have an existing proctor curve b/c of the preliminary geotech report, and that this is what is slowing things down. i'm sure this would be good enough for some people, but i would require another if i was running the testing department. Proctors in the geotech report are there to give the design team an idea of the suitability of on-site soils.

When you say the County is the inspector, does this mean that the guy/woman on-site is a town employee? or is the inspector employed by the County to represent them and they work for a variety of other clients?

I refuse to believe that a Proctor test with a 1-day minimum delay for every SINGLE test is standard industry practice anywhere. Especially, since only testing for wet density is in-my-very-honest-opinion inferior and goes against standard industry practice. I am from the east coast, however, and i recommend you call some local testing firms and get there opinions on this test (make sure you speak with ones that do Transportation work). i suspect that they will agree and will chat to you for free.

i wonder if the original intent of this test was to speed up construction compared to typical field testing methods. I also wonder if the inspectors are either missing the point or are not comfortable with the test and are taking it real slow. (i also wonder if you're giving us the full picture. you are a contractor after all! Hah!)

if the testing is done by a company that serves the County, you'll have a good shot of getting the Civil Egr to agree that compaction testing identified in (insert any Master Specification publisher used extensively for construction) is acceptable. if it's done by the County, the X-factor is their bureacracy and how it could affect recommendations.

i have to think that it is in the County's best interest for you to finish fast and get out.

 

[emmgjld]

Oldestguy

Committee D-18 is reapproving D5080-00 TEST METHOD FOR Rapid Determination of Percent Compaction.

I had forgotten about this procedure. Basically, the method is using the wet weights, both from the in-place test and a 3-point proctor curve to get a quicker, approximate answer.

 

[msucog]

"rapid"...so then you gotta confirm. why not just run the test in the first place? if the rapid test ends up showing a better compaction and then it comes back low, someone is going to look like an arse in the eyes of the contractor and owner who don't understand what we do anyways.

and proctors from geotech report are good for general info but field proctors during construction are absolutely necessary. it may all be essentially the "same" material but adding them together changes gradation, weight, etc. during the geotech report, i doubt there's pans running everywhere picking up dirt from here and there and then laying it down as fill. i often have jobs with 20-30 proctors...might not charge the client for all of them if i get repeats but at least i have a better feeling that my results are good.

 

[BigH]

msucog - that was the beauty of the Ontario way of doing it - you used the same material that had been compacted to make the "field proctor" (all: let's not quibble about a bit of additional particle breakdown on the "field proctor". But, it was slow. As another thought - don't they let you use speedy moisture meters anymore?

 

[msucog]

i'm not fussing over field proctors versus lab proctors for you average soil with little to no oversized particles. i'm talking about grabbing a bulk sample out of a borehole versus grabbing it from a soil stockpile that is about to go in as fill. here in the piedmont we see the proctors range from 80-125pcf and the geology is a mish-mash of stuff with multiple geologies on the same site. and the number of proctors usually follows the size of the site...the 20-30 proctors would be on a 100-200 acre site which is bigger than most sites.

all in all, it's sort of like running a proctor in january and then coming back a year later after 20' of soil has been moved around the site and using the same proctor. at a minimum, the tech should be running checkplugs daily to get them on the best proctor. however, i would have another proctor run...it's a relatively inexpensive test and worth the effort.

 

[kurtjfred]

Hey Darth, thanks for your input. I'll give you some more info to try and clear up any more confusion.
The project is a sewer line being installed for the county. The county put the job out to bid, are paying for the installation and will own the line. They are the inspection, and code enforcement agency for the project. They wrote the bid specifications and most if not all refer back to CalTrans specs. The inspectors are county employees and not subcontractors. They have a county lab with techs that are doing the testing as they do with any of the jobs that take place under their jurisdiction, such as any subdivisions or commercial projects that don't fall in the city limits or jurisdiction of the state like a highway might.
As I stated earlier, I have done civil underground and grading in California for over 25 years for both private and public ie: Caltrans, counties, state, and federal projects. Subdivisions, site work(shopping centers,commercial pads to school and airports) and lots of highway and street work. %99 of this has been in Northern California.
I think the job we are performing is overwhelming them. I know that they don't have the resources to cover the amount of work we are installing and how fast we are performing and they have yet to hire outside help like I have seen done in the past when this was occuring. They are making it my problem. I don't want to get into the legal ramblings, the timely inspection owed and all the other technicalities. What I am trying to resolve is the soils compaction method (a successful method) and the timely results of testing.
As I originally asked, I am trying to find a source of information that can explain in great detail about the ASTM Proctor tests, wet density, dry density, methods of determining them.
Where does the soil sample have to take place in relation to where the gauge was placed on the ground, in what time frame does the soil sample have to be taken in relation to when the gauge was placed on the ground. Even if a wet density test is being used, could the lab work and curve have already been pounded out. The trench is surveyed and you could return to the same spot(within inches) to place the nuke gauge and test compaction. These are the things I am trying to determine as well as recommended tools and methods for compacting silt and sand. I am using compactions wheels on Komatsu 220 excavators right now.

 

[AZEngineer45]

Wet density is dependant on moisture where dry density is not. That is to say a wet density taken today might be 134.5pcf with an accompanying dry density of 124.5. If you take the test tomorrow in the same location you might get a wet density of 133.5 but still a dry density of 124.5 - DRY DENSITY IS EXACTLY THAT, not influenced by moisture as the mosture is taken out of it mathmatically. We run densites here and provide contractors instantaneous results for acceptance. If a person does not know the theories behind density, moisture, unit weight / proctors /rock corrections and gauge bias, they will not be able to provide instantaneous results. Have the technician run a sand cone correlation against the gauge to determine unit weight and moisture bias and the lab run a method C proctor (assuming you have no rock greater than 3/4" which is probably the case in SoCal...

It's not brain surgery but I have been doing it for 18 years. It's also not so easy that anyone can do it. It provides a well rounded informed and TRAINED individual in the field to provide accurate and timely information.

It should also not take a day as if they are running lab oven dry samples, the same could be done using a calibrated speedy moisture tester that was calibrated in the lab against varying materials at varying moistures and establishing a correction curve....