Soil Compaction
Soil Compaction
(OP)
Hi
Just a few questions on compaction.
Is there any correlation between Impact Value (determined by site testing using a Clegg Hammer) and Density?
What are the methods used to determine whether compaction has attained 95% or 100% modified density.
What is the best way of determining if the bottom of a fill is compacted? Does excavating to the bottom disturb it enough that additional prep work has to be done before it is tested?
Thanks
Just a few questions on compaction.
Is there any correlation between Impact Value (determined by site testing using a Clegg Hammer) and Density?
What are the methods used to determine whether compaction has attained 95% or 100% modified density.
What is the best way of determining if the bottom of a fill is compacted? Does excavating to the bottom disturb it enough that additional prep work has to be done before it is tested?
Thanks





RE: Soil Compaction
A sample of soil, (in situ), is measured for volume and weight and is compared to the maximum density achieved by the proctor run in the lab per ASTM. Variety of methods to measure soil in place density; sand cone, nuclear gage, shelby tube, etc.
Bottom of the fill:
1) during construction, test and record the density of each lift at random locations per testing schedule.
2) after completion, drill to elevation in question and push a shelby tube to obtain a sample or excavate a pit for tester to check density.
RE: Soil Compaction
As for methods to determine percent compaction, you have the lab determine the moddified Proctor density. You then determine the in-place field density via (sand cone, nucular densometer, drive tube, bulk sample, water ballon, etc.) and compare the densities.
As for methods to determine "...if the bottom of the fill is compacted?" you need to give us some more information. Are you saying that the fill was placed to some significant depth and no tests were taken and now you want to know if it was done correctly?
RE: Soil Compaction
The site has already been filled and no tests were taken.
Civilperson....are you saying that you can't excavate and then test?
If a fill has been compacted to spec...say 95% modified proctor and then exposed to rain, can this impact the compaction test results? If so, then it leads back to my previous question. How do you determine where the compaction is still acceptable so that we can establish how much material needs to be removied.
The Clegg hammer is a simple impact hammer that is commonly used to measure "stiffness and strength". They come in different weights and are dropped from a specific height and the decceleration of the weight is measured.
Thanks
RE: Soil Compaction
RE: Soil Compaction
As for compacted soil exposed to rain, etc. Yes the percent compaction for the upper 1/2 to 1 inch will be effected. But deeper within the fill, there should be pretty much no effect. If the fill is only a couple of feet deep a trench could be excavated with tests taken either in the bottom of the trench as it is excavated or in the sides of the trench. However, if the fill is several feet deep, a drill rig pushing Shelby tubes would be the better way to go.
That said, if no one was watching the fill being placed and compacted; no one know what might have been burried in the fill. Could be ok, but could also have a car incorporated into the fill.
RE: Soil Compaction
i'm not aware of Clegg so i can't comment on that. i hope this helps a little.
RE: Soil Compaction
RE: Soil Compaction
RE: Soil Compaction
I'd say it depends on how deep your fill is. Like BigH said, you can start out with a test pit and do a density tests(sand cone, if you don't have the license to use a nuclear densiometer), but you can only go 4 feet in the states without danger of wall collapse. Using the N60 value with an SPT (drill rig) would be expensive, but if your fill is very deep; on the order of 10-20+ feet, it would be more feasible to just take the N60 value and try to correlate stiffness. You could at least compare the upper layer results (probably more compacted, or you could have them roll it) to your lower layers and see if there's any difference in the blow count. Just depends on the depth of your fill.
If you're wondering about methods of density testing go to the ASTM website and look up nuclear densionmeter and sand cone methods. That should pretty much cover your bases, if you don't have a local testing lab to call.
RE: Soil Compaction
"no good deed goes unpunished"
RE: Soil Compaction
RE: Soil Compaction
In the other hand, in field, having or not the maximum dry density established in lab you can correlate th IV to certain field density and moisture content values by using any of the avaiable test methods to determine on-site density (nuclear gauge, sand cone, rubber ballon, etc). Impact Tests are performed in a place and then compaction or the field density is determined.
I'm not saying that test is flawless, some considerations should be made, for instanse, oversize particles, in any of the compaction methods you can determine a corrected density (field or lab) following the procedure described in ASTM D 4718, however, how these oversize particle may affect the IV, my best guess is doing something like nuclear gauges technicians commonly do, excavating by hand the testing point to observe the soils surronding the test hole, speecific information related to IV test is included within ASTM D 5874
Regarding to bottom of the fill is compacted, I have participated in some forensic jobs to determine if compaction was reached in some embankments and the procedure used was firstly established in a meeting with contractors, project owner, laboratory , if any other firm is participating, and commonly the agreement reach is, perform the first test on top, then partially excavate the layer, using a construction equipment (usually a backhoe)and complete the excavation by hand to the top of the next layer and perform the next test, this procedure is followed until bottom is reached (certain conditions requiere a safety plan for trenching, it is certaing disturbing degree, nevertheless, is there any sampling method in soil testing that not induce certain disturbace in samples?, generally speking, geotechnical engineers and cmt engineers have to work with soil samples as reasonbly undisturbed as can be obtained, so that is why a procedure should be agreed and signed by anyone involved before testing starts, just to avoid that if test results were different to those expected by any of the involved part, no one can come out and said that procedure used to reach certain depth is not adequate, or ask for a re-test or use it as argument in court.