sample pipes in SPT?

[fattdad]

Hi All,

We have an ongoing field exploration and the driller is driving samples with non-a-sized-rod. Maybe N-rod or such? I can certainly get those details in the days to come. My question is whether there are unique terms we'd have to use to normalize the SPT N-values ala N1-(60)?

D6066 is the ASTM standard and they seem silent on the matter.

Thoughts?

f-d

ípapß gordo ainÆt no madre flaca!

 

[GeoPaveTraffic]

I believe some work has been done looking at the effects of different size rods, but I don't have those details in front of me. My recollection is that the effect is small. I have never worried about rod size given the other "imperfections" associated with SPTs.

Mike Lambert

 

[fattdad]

Yes, I also want that to be true!

We are seeing some interesting data; however. Low N-value intervals in an old marine deposit (Coastal Plain, Virginia) that we haven't seen in other borings. Wondering if the heavier weight of the larger rods are forcing the sampler to, "Fail" the soil strength without any blows. Seeing WOR/WOH data and just noodling over the, "Why?"

Thanks for your considerations!

f-d

ípapß gordo ainÆt no madre flaca!

 

[Okiryu]

f-d, I think that if the N values are used for design, it should have some concerns. Since you mentioned that have other borings in the same area, perhaps a correlation between energies (from the typical and heavier loads) and SPTs can be done.

 

[fattdad]

Thanks Okiryu! I'm sure we'll do such correlations. That said, not sure they'll be of much value as the other efforts predate the safety hammer and then predate the automatic hammer. We'll know more when the cones are put in the ground.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

FD: With so many other things affecting the N value, I'd not be concerned. It's a very crude test.

 

[Ron]

f-d...as you know, N rod has a larger diameter than A rod, but it has a thinner wall. I have not run the calcs, but N rod is likely stiffer than A rod, particularly when the soil resistance goes up and the compression wave from the hammer goes down the rod. Read Schmertman's paper on the SPT energy correlations, "Energy Dynamics of SPT", Journal of the Geotechnical Engineering Division, August 1979.

 

[fattdad]

Dear All,

We did the calculations and for below water application, there is less than 100# difference between 150 ft of A-pipe and 150 ft of N-pipe. I feel better now.

f-d

ípapß gordo ainÆt no madre flaca!