"compaction" tests in residuum
"compaction" tests in residuum
(OP)
I understand that compaction tests are impractical for residual soils. Does anyone know of a paper or reference speaking to this issue?
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
"compaction" tests in residuum
|
RE: "compaction" tests in residuum
A compaction test is just a density determination compared to a standard. Therefore, they can be conducted on any material.
If your question relates to making judgements about "natural" soils by comparing a density measurement to a standard, then I would say that is meaningless not just for residual soils but for all soils.
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
a) strip the top soil and replace with compacted fill
b) compact the top soil in place
c) test the top soil for in-situ density and evaluate
d) allow for the settlement in the design
I would not say the tests are impractical and we often require minimum density for the subgrade, even if it is topsoil.
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
Thanks, everyone, for trying!
RE: "compaction" tests in residuum
At the least I would require proofrolling for uniformity. It only costs a little more to check and achieve reasonable compaction (95% of Modified Proctor)if the soil conditions are good. Then you'll be able to sleep a bit better and you will have met your professional standard of care to fend off the lawyers if something does go wrong.
RE: "compaction" tests in residuum
vollEngineer, Assuming that the soil is clay or silt, i.e. cohesive; I would say that density is not a valid measure of soil strength or allowable bearing capacity. Soil structure has a lot to due with the strength of the soil in these conditions. This seems to be your opinion as well.
As for your client, tell them that it is not necessary to excavate and recompact the soil, but if that is what they want to do and they have the money. I say go for it. You got nothing to loose and the client is the one who is making a bad choice and costing him/her self the money.
Clients are like horses, you can tell them what they should do, but it is there choice to drink.
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
Here's where the body is buried: Let's say the natural soils have some favorable undrained shear strength (e.g., some residual micaceous silt or clay) and let's say the moisture content is at 95 percent saturation. Let's say you "check" the compaction and it's at 90 percent. You (incorrectly) run the compaction equipment over the subgrade and because the natural soil is not at a favorable moisture content for compaction, you stir up a subgrade of mud. WHY? Do you blame the site conditions" Do you blame the contractor? Should the owner pay? There's no good reason (if the original geotechnical study was complete), it's not a changed site condition, the contractor was following "spec," but the owner should not pay (but likely will).
If the OP relates to cut-to-fill operations, then sure use a nuke gauge (for the fill placement). If the residuum has mica, do a few lab mositure contents to make sure you are not being affected by the mica (or field burn offs).
If you have a natural subgrade that's become disturbed by construction, it needs to be repaired. Dead reckoning will tell you that (or a proofroll) and any repairs will likely entail fill placement, which requires compliance to the earthwork spec.
Sorry for the long post.
f-d
¡papá gordo ain't no madre flaca!
RE: "compaction" tests in residuum
I think one of the lessons learned, here, can be that the geotechnical engineer should have the opportunity (and take it!) to review the drawings and specs during design to ensure these erroneous interpretations of fill recommendations are kept out of the specs during construction. If we had reviewed the specs during writing, we might have helped the architect avoid this confusion. It's much more difficult for architect, contractor, owner, building official, and inspector to change them now that we're under construction.
RE: "compaction" tests in residuum
the writer of the specs likely hasn't updated the specs in 20 years and probably doesn't understand half the things in there. i'd dare to say they don't even understand the difference in standard and modified proctors much less the difficult topics such as foundation support. assuming you're the geotech, do your client a favor and get it fixed. also, if you ever end up in court, the lawyers don't care what is appropriate...if it's left in the specs (ie. CONTRACT documents), then it could be a sticking point for someone to try and kick you...simply because you didn't follow the contract. (not saying it would work but you've still got to spend money/time defending the ridiculousness that the opposing lawyers come up with).
RE: "compaction" tests in residuum
I got quite a setting back once when the contractor was not getting 95% in a clay. He asked us to test the cut material as it sat before being excavated. It had an unconfined compression value of a few tons per s.f. I'ts "percent compaction" was 82.
Contractor's question was why we allowed him to build on that undisturbed clay at its condition and wanted 95 in the fill?
Why dry the stuff out to get that spec. when in a few years it would revert to its former moisture content.
Then, another job comes along where our inspector enforced the 95 percent in a highly plastic clay. Later the buildings (plural) were all distorted as the clay took on water reverting to its former condition. A very embarrassing situation I tell ya.
The subject is not that clear cut for the average job.
RE: "compaction" tests in residuum
RE: "compaction" tests in residuum
Residual soil/completely weathered bedrock in our local has shown from post-construction distress in roadways and structures that the new improvements change drainage conditions. Where water previously did not accumulate in the soil, it did after the construction. Over time pavement subgrades that were resistant to deformation, and difficult to cut, saw that strength degrade with moisture development. Completely weathered siltstones/claystones in some cases behaved well, and in other cases expanded and lifted improvements.
The question that I bleieve needs to be addressed with these materials is how will the material's behavior will change to the likely changes associated with changes in the residiums moisture contente with time. The answer to this question is your guide.
RE: "compaction" tests in residuum
I would also second your opinion that the geotechnical engineer be retained to review the plans and specs. I cannot tell you how many times I have run into this - or similar issues - that could have been resolved by properly educating the architect, owner, and/or local byuilding officials about what we do.
RE: "compaction" tests in residuum