Scott, the THD penetrometer is most likely identical to the standard CPT. I used to work for the Dept of Main Roads in Queensland, Australia, and they had there own method of CPT, but it was identical to the Australian standards. Most government departments will have there own test methods or, method numbers. It would be to your advantage to phone Texas Highways and ask if it is modelled from your national standards, whatever they may be. By memory a standard CPT is the centimeters drop to the number of blows. Calculating these into a formula will give you an insitu CBR value. Regards. Kane Kreeck.
kreecky@hotmail.com.