Hello everyone!
I have been doing Level 1 Inspection & Testing for Soil Compaction in the field. The compacting material is basically, CLAY. I use nuclear gauge to measure the field density and moisture.
I wanted to have the expertise suggestion on "how can we say if the moisture is OK or NOT or simply if the moisture that is used for compaction is within the design limit like +_2% or +-3% of OMC". I usually, use this feel method by hand but that is way too confusing to tell and it's subjective. Yes, there is one method to tell that is carrying out one dummy test, however, by the time the dummy test finishes the lifts would be laid and compacted.
So, I was wondering if there are any suggestions in this regard from the experts. Even if the method is feel based, I shall be thankful to have a bit more explanation so that I can implement in the field from next time.
Thanking you in advance.
Sumit Maskey
Dear Sumit,
The test results which you had conducted in the field are to be compared with laboratory test results or needs to compared with the moisture recommended by the expert. Based on the analysis if results are closely matching with laboratory results than it shows that the desired compaction achieved in the field. I feel 5 % error is allowed in geotechnical engineering. ok all the best..
Clay is usually compacted with sheepsfoot rollers because smooth rollers tend to sink into the soil if moisture content is too high and if it is too low then the chunks of clay would not yield to rolling. Sheepsfoot rollers are most effective in breaking the clay clods and filling large spaces depending of course on the size of the roller's feet. Therefore a poorly compacted clay might show non-level areas or areas heaving under load (when a person walks or a car drives over them) indicating voids underneath. I don't think that there is a way to estimate OMC by feel.
Karthigeyan . S & Thomas Makedon
Thank heaps for your valuable time and comment sir.
Yes, I always perform a quick dummy test in the lab at the site & also check if the CLAY clods are sticking to the foot of the compactor (Padfoot). However, I wanted something quicker out there in the field to guide the guys placing & compacting the lifts. For instance, how the experts do, "grab the soil in the hand --> squeeze it --> & say, if the soil should be dried or should be wet [not telling or looking for the OMC but to see if the placed soil has got the moisture inside the the design moisture window like +-3%]
Sumit
It depends with the type of soil. Saturated clay soil can feel fluid upon squeezing. For sand or gravel with fines you can see it binding andfeel slippery while poorly graded coarse aggregates with no fines are difficult to see because of not much water absorption
In a pinch, rolling a test pad can be helpful, especially where the fill being placed is variable having a range of plasticity or fines content. Simply construct a lift in a small area, compact using multiple passes and test with a nuclear gage between passes until no improvement in density is achieved. Then adjust the moisture and conduct another small lift comparing the achieved density between lifts at different moisture content.
A practice I used to use for manual/visual checking, was to collect samples from the Proctor test mold in the laboratory at a known moisture content at or near optimum, preserve them in small sealed jars, or bags to be used for reference in the field. This enables the field technician to compare both the material type and moisture to the lab sample. The samples will, of course, dry out after repeated opening of the container, so it is good to have multiple duplicate specimens.
Regardless, if quality is important, the compaction activity, must be done in a way that permits verification. If the fill gets ahead of the testing, excavate small hand dug pits to test deeper layers. There is little point in constructing a deep fill, that will not meet compaction requirements that results in unsatisfactory performance or failure later.
By feel and squeeze one can tell if the moisture in the clay is workable or not,once clay is sticky it means it has more moisture than the OMC and when clay is squeeze and the bond between its portion can be broken easily, it means the moisture is below the OMC, so its all about striking the balance while you are at site.
Michael Byle Thanks heaps sir...I've been doing the same thing :) :) Conducting a Standard compaction dummy test in the lab before hand & collecting a jar of sample which is nearest to OMC and making few extra specimens that's inside the moisture window as per the spec. I would take this sample & show it to the moisture conditioning guy to direct him/her :) :)... Thanks once again sir :)
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