pq test
pq test
(OP)
Recently a large multinational construction firm requested that we do a soil investigation for a project. What we find odd, is that they "required" soil capacity to be determined using a pocket penetrometer. How common is this elsewhere? My experience in using the pq is that it is not terribly reliable. It may be ok for the field as a reference to a complete soil report, but not for providing recommendations.
What are your thoughts, particularly in relation to its use in giving recommendations elsewhere.
What are your thoughts, particularly in relation to its use in giving recommendations elsewhere.





RE: pq test
If you propose on it as was requested, with bearing pressures determined using a pocket pen, it could come back and haunt you.
The only case I can think of where it would be of much value is if you needed a rough estimate of short-term bearing capacity for a fndn on clay (so the pocket pen can give you an estimate of undrained shear strength you could apply in spread-footing bearing capacity calculation with phi=0).
Best regards,
DRG
RE: pq test
RE: pq test
RE: pq test
f-d
¡papá gordo ain't no madre flaca!
RE: pq test
Judging by some of the questions in other posts, and this information, I wonder how things are in other areas of the country, and if this is the general direction of the industry. This certainly isn't the case for all architects, contractors, and engineers, as some definately know what it is they are doing and needing in regards to testing.
RE: pq test
(Still, I regard the pocket pen as more of an index property to use in logging samples in the field, or at the ends of Shelby tubes when opening undisturbed samples, not something whose results I would use to design a cut slope of any consequence.)
It isn't necessarily ridiculous to do a soils report using only auger samples. All depends on the situation. If the guy knows the local soils well, that may be all he needs for the purpose at hand, if it's light residential, a cut slope in sand and gravel, or something like that, where knowing the material descriptions could be sufficient. For a heavily loaded structure or a steep cut in clay (where Su is critical), that's not likely to be adequate.
RE: pq test
I don't see much of a bearing capacity issue. I do see a lateral earth pressure issue, which should include a piezometer in the fat clay, just to see if you can get hydrostatic conditions from partings in the clay. I also see an issue on backfill materials. Just how will the excavated fat clay perform during backfill operations (i.e., will the contract requirements specify 90 to 95 percent compaction when the excavated soils are slow to dry and saturated)?
The field program needs to consider piezometers, Shelby tube sampling, direct shear, UUTXC and likey a 1-d consolidation test (just to look at the extent of preconsolidation). That said, I'd still require the field exploration to include pocket penetrometer tests on all SPT test samples (and Shelby tubes also). Just for reference, the test program that I'd suggest would likley be less than $2,000.00 in many of our local markets. Where our profession is going downhill is engineers are having a hard time marketing the necessary data (and shade tree geotechnical firms are willing to under price what's needed).
f-d
¡papá gordo ain't no madre flaca!
RE: pq test
Question, is the UUTX an abreviation for the triaxel test? Thanks.
RE: pq test
If there is a battery of testing on "undisturbed" samples and these data were used in the overall engineering analyses, then I'd also want to use a pocket penetrometer during construction to document (qualitativelly) that the soils in the field relate to the soils from the design field exploration.
Sounds like an interesting project.
f-d
¡papá gordo ain't no madre flaca!
RE: pq test
RE: pq test
RE: pq test
I pointed out to an architect the other day that the reason his building cost so much wasn't because the structural engineer had been conservative (for some reason they blamed the poor structural guy) it was because the geotechnical engineer had given them allowable bearing capacity of 2500 psf for clean sands with SPT blow counts of 80. But I think they went back to that same geotechnical firm for their next building because he was $5,000 cheaper than me.
On UUTXC, my practice has been to consolidate the samples (drained) to slightly more than the in-situ stress and then shear them undrained. I figure the strength gain from the slight extra consolidation won't be significant and the consolidation should remove some of the effects of sample disturbance. I'd be happy to be talked out of that though.
RE: pq test
RE: pq test
CUTXC is a different test, which is first consolidated. UUTXC takes the Shelby tube sample and replicates the in-situ stress with out consolidation, then shears without drainage. You'll get the undrained shear strength at that confining stress.
f-d
¡papá gordo ain't no madre flaca!
RE: pq test
RE: pq test
f-d
¡papá gordo ain't no madre flaca!