Current Sampling Equipment?
Current Sampling Equipment?
(OP)
Hi all, experienced and new geotechnical engineers...
How does your firm obtain relatively undisturbed soil samples? My current employer seems to have massively outdated equipment in the lab and in the field. I am curious as to what is the most widely used equipment for field sampling at this time. We use a modified California ring sampler, but the particular brass or Teflon rings we use are no longer available for purchase and have not been available for quite some time. I have only been doing this for a little over a year now and need to know if working here is essentially a time warp into 1960.
Mahalo!
How does your firm obtain relatively undisturbed soil samples? My current employer seems to have massively outdated equipment in the lab and in the field. I am curious as to what is the most widely used equipment for field sampling at this time. We use a modified California ring sampler, but the particular brass or Teflon rings we use are no longer available for purchase and have not been available for quite some time. I have only been doing this for a little over a year now and need to know if working here is essentially a time warp into 1960.
Mahalo!





RE: Current Sampling Equipment?
There are methods of getting relatively undistrubed samples. The one we use most often is a Shelby tube. Typically a 3-inch diameter by 24-inch long sample. Two inch and 5-inch diameter tubes are also generally available.
The only other option I've seen specified is a Pitcher sampler, though I've never used one.
Mike Lambert
RE: Current Sampling Equipment?
Other methods to obtain relatively undisturbed samples might be by the use of the Swedish foil sampler - but I doubt this has been used more than a few times outside of Scandanavia . . . you might find something about it in a book. Our company in Canada had the rights to this sampler - but it had been used years before I had joined (1975).
If you are in test pits, then the use of block samples would be appropriate. See USACE, Hsorlev for how to take the sample.
RE: Current Sampling Equipment?
In much of the south, the clays are stiff to hard, and the main question is how much will the soil swell. The standard sampler is a thick-walled 3" tube that looks like a Shelby tube, but the wall is thicker and the tip is not swedged to cut an undersized sample. Some drillers are still using the tubes they started with 20 years ago. When they get nicked and bent on the tip, they saw them off. The more picky ones grind the tip sharp, but some just use the blunt cut end! The recovery is poor, but improved by pushing a 16-inch long tube 24 inches.
You probably won't have to try very hard to improve on the local practice. Read Hvorslev and recognize the principles. Are you concerned about reducing the undrained strength by remolding the sample too much, or increasing the apparent strength by compressing the sample due to high perimeter friction? buck the tide and try to improve your profession.
For more important strength and consolidation testing, Shelby tubes are still the standard. Piston samplers or foil samplers may be justified for very soft or sensitive soils. Larger-diameter Shelby tubes generally get less-disturbed samples. Don't over-push the sampler, and reduce the push to 12 inches or so for touchy soils.
Don't knock the 60s. Academics, in-situ testing,and computers have improved since then, but the local practice has deteriorated since the geotechnical report became a priced commodity.
RE: Current Sampling Equipment?