Shelby Tube Length

[DPirate]

Hi All:

I've questions about the length of the 3"OD Shelby Tube sampler. AASHTO T207 (ASTM 1587) Table 1 lists the length as 36 inches, with the proviso that "Lengths of tubes are illustrative. Proper lengths [are] to be determined as suited to field conditions." My question is how do you determine a 'proper' length? I've encountered a four-foot sampler in use; I haven't obtained test results as yet to correlate data compared to a three-foot sampler, but should I expect to see a difference in the two?

Thanks for any enlightenment!

 

[BigH]

We used to use 30 inchers, but not actually true shelby tubes so we called them thin-walled samplers. The stiffer the soil, the shorter your tube would likely have to be in order to get penetration using your jacking/hydrulic push. That is likely what they mean. I believe that if I was in a very stiff clay and I had the push to penetrate, I would likely only go 18 inch tube or so. Of course, you will not always fill the tube you go with - depends on the site conditions and what you are capable of doing. Anyway, that's my take on it - although I've been "out of the field" for years, I do remember the -25degC pushing in the thin walled tubes and keeping your car running the entire shift in order to keep the heater going so the samples wouldn't freeze.