SPT, ASTM Standards 1

[sapperzues]

I am argueing with a college reguarding the ASTM standards for my Standard Penetration Testing (SPT). I have been through the D2937, D3550-01 and D3740 standards but can not find an absolute as to the N-value and the need to disclose a "no-recovery". I am contesting that the N-value is fifty and must be maintained for accurate repair data findings. It is also my contension that "no-recovery" or "NR" must be disclosed. If you have a copy of the ASTM's reguarding these subjects please E-mail them to me. I can not find the answers in the ASTM's. Maybe I am looking in the wrong ones.

 

[BigH]

Sorry, I don't have the ASTM's with me. I'm not quite sure what you mean by "... the N-value is fifty and must be maintained for accurate repair data findings."???? As for the reporting of the NR, it was our company's policy to so report. Losing a sample might be for a number of reasons - no trap in spoon for sands, very soft clay, etc. However, if we lost it, we almost always made an attempt to try to recover the material by use of a spoon-side sampler as given by Terzaghi and Peck (1967). At least you had a sample to view and describe.

 

[sapperzues]

Thank you BigH, the N-value is the amount of resistence at the bore point to safely call the job done. I am still looking for a standard on this. Please let me know.

 

[BigH]

We used to use 100 blows as the maximum blows in the "N" range of the drive. However, there is very little to be gained if you have driven 40 blows per 1 inch of penetration, as an example. A lot depens on when enough is enough. It is not always a question of "codes" but of experience. If I have a soil that has an N value of 70 or one that is 80 - doesn't really mean much does it? Also, it depends on the materials in which you drive the spoon. If you know you are in bouldery till or gravelly sand, you will be having strong influences of such larger pieces that won't fit into the spoon - again, what good is it to drive the spoon to where the tip is badly damaged. My view, my friend, is that instead of worrying about codes, etc., one should gain the experience and confidence in applying your judgment to the situation you have. As for the codes, you might not want to look into the code of doing the test - for it is a test method, but for a code relating to the geotechnical investigation (sorry, I don't have the ASTM books with me here in India to figure out which is applicable). You might wish, too, to check out British Standards Codes of Practice.