I am looking at a soil report that I need to use to design a foundation. Maybe I should first mention that about 75% of the text of the report discusses what was not done and what is not covered, and some information on local tort law.

In the text of the report, there are three locations that are listed as having c less than or equal to 2000 psf. When I look at the boring log, these locations all have penetrometer readings of 4.5 TSF, just like all the other tested depths. When I called the soil engineer to ask about the discrepancy, I was told that there was only 66% recovery in the shelby tube at these locations. So they provided a design value of 66% of the measured value. They have correlated c with 1/3 the penetrometer reading. So 4.5 TSF / 3 * 0.66 = 1 TSF = 2000 psf.

Two questions:
1. Is it typical to reduce the cohesion by the % recovery? I have not seen this before
2. If the soil is "loosely compacted" as the soil engineer suggested on the phone, does compression by the shelby tube actually increase the measured penetrometer resistance of the soil as the engineer suggests?

Thanks!