Compaction Specification - 5% air voids
Compaction Specification - 5% air voids
(OP)
I am wondering if anyone has experience with using a specification for earthworks based on achieving a minimum air voids percentage?
My theory being that:
1. material placed dry of standard optimum moisture may have satisfactory performance when you proof roll - but will deteriorate over time.
2. material placed dry of optimum will swell under low overburden.
3. material placed dry will collapse under high overburden.
Any thoughts?
My theory being that:
1. material placed dry of standard optimum moisture may have satisfactory performance when you proof roll - but will deteriorate over time.
2. material placed dry of optimum will swell under low overburden.
3. material placed dry will collapse under high overburden.
Any thoughts?





RE: Compaction Specification - 5% air voids
RE: Compaction Specification - 5% air voids
An awful lot of dams have been built dry of optimum and still hold water, and on a high embankment, it has advantages in limiting post-construction settlement and excess PWP.
I believe BigH is correct on 1, 2, and 3.
DRG
RE: Compaction Specification - 5% air voids
Minimum air voids percentage is something I've never seen, and the logic for it eludes me. Seems to me that you could just place your fill wetter and achieve the minimum air voids requirement without achieving good dry unit weight. Just for context, is this something you are proposing to do, or something that is being forced upon you, or what? What is the purpose of the earthwork (dam, highway, landfill liner...)?
RE: Compaction Specification - 5% air voids
Sounds more like an asphalt spec.
Have never seen such a specification for soils.
BigH is correct on 1,2, and 3. ( Or at least I agree with him and I also assume that when anyone's opinion is the same as mine, that person is correct by default!!
RE: Compaction Specification - 5% air voids
RE: Compaction Specification - 5% air voids
Primarily talking about medium to high plasticity clay fill for road embankments.
BigH - When modified specified I assume that you also compact to somewhere around 95 to 98% modified?
When you say way dry, how far? A specification is allows for 60-90% of OMC.
Ron - I have attached a standard compaction plot. Looks to me like 5% (or 10%) air voids would be reasonable.
RE: Compaction Specification - 5% air voids
Is their goal to optimize compaction and saturation on an equal basis?
RE: Compaction Specification - 5% air voids
I've had many discussions with some or my junior engineers years ago - for foundations (under them) I always specify MP MDD, even if I use 95%. They wanted to use 98 or even 100% SP MDD. I won as my name went on the report. The MP test could be called a "hernia test" - but by specifying this (or heavy compaction for the Brits), you are telling the contractor that this IS IMPORTANT; where when you specify SP (standard Proctor) many contractors and testing companies might get a bit lazy.
By very dry of optimum - you will find in the literature that you can have a higher dry density at very low moisture content - it might not be as high as the "real" peak but it can be there. I found it in India with a mix of fly ash and sand - which exhibited "two" peaks depending on the moisture content.
By the way - I try to stay away from moderate to highly plastic clays for embankment fills if at all possible. Have never had to deal with the use of such materials for fills very often . . .
RE: Compaction Specification - 5% air voids
RE: Compaction Specification - 5% air voids
When specifying placement criteria for compacted clay liners, for example, compaction moisture content is critical as when you are less than about 90 percent saturation the permeabilty is affected as much as two orders of magnitude.
I just don't think research shows that your conditions 1 through 3 are typically true.
Not to digress too much, please recognize that optimum moisture content for 100 percent compaction is not the same as optimum moisture content for 95 percent compaction. Just like there is a line of optimums that parallels the zero air voids curve (i.e., as referenced above, the optimum moisture content for modified proctor and standard proctor line up with the ZAV). This whole topic of material properties and optimum moisture content looses focus when your placement criteria accepts 95 percent proctor. This is true whether you are considering modified or standard proctor.
f-d
¡papá gordo ain't no madre flaca!
RE: Compaction Specification - 5% air voids
RE: Compaction Specification - 5% air voids
BigH - in your post on 4 Apr 11 you say "way it has always been done". I agree to a certain extent. As you also say, most of the time we try and stay away from moderate to high plastic clays. Sometimes this cannot be done. In that case I don't know that experience that is gained for low plastic clays can be applied to moderate to high plastic. At least not without a lot of careful attention.
I also think it is one of those things that, to tell the difference between a good and a bad compaction specification could take upwards of 10 years. And then to nail down that the poor performance (i.e. ride quality on a highway) is due to the compaction specification would be a very costly and time consuming process.
RE: Compaction Specification - 5% air voids
You are correct in that highly plastic clays are a different animal and I indicated that I tried not to use clays at all in fills - although I know that there are times that it must be done. For HP clays, one needs to know the effects of swelling and shrinkage due to moisture migration - both from the initial compaction moisture content and 'final' - but what seasonal changes might occur. I understand in California they use 85% compaction levels in many fills for this reason when dealing with such materials. One also might wish to use lime or other additives to reduce the level of plasticity - so when one deals with moderately to highly plastic clays there is really a solid need for treating the compaction level and equipment with a higher level of care.
RE: Compaction Specification - 5% air voids
Yeah, compaction is great, but if the topic is plastic clays, be careful about the long-term performance!
f-d
¡papá gordo ain't no madre flaca!
RE: Compaction Specification - 5% air voids
RE: Compaction Specification - 5% air voids
f-d do you have any references to the work you talked about?
I will have some more reading to do.
RE: Compaction Specification - 5% air voids