What I do for cohesive soils is pretty straight forward: (Q(t)-effective overburden pressure)/Nk
Qt: Is the tip resistance corrected for pore water pressure.
and Nk will vary between something like 11 to 18 depending upon the soil conditions.
However, in sands it gets complicated, its based upon the relative density of soils. I am still trying to figure that out. There is a software called CPTINT published by University of British Columbia. Can't seem to find it anywhere. Anyone else have it?
I'm not sure if there is any commercially available software for this sort of thing. Check publications by Robertson, Wride, Lunne, etc... I know I used Peter Robertsons papers extensively in my Master's research. One of the best bets for sand CPT work would be to review the CANLEX data in the Canadian Geotechnical Journal (most of which should be available on line from Natural Resources Canada).
The free/shareware CPT data interpretation package that you are seeking is available from the Univ of BC Engineering website. It is now considered free shareware as it is no longer supported.
After you get some output from the CPT interp program then I would recommend that you double check the output with a spread sheet of your own design.
I have found that it is necessary modify the results a small amount based on the area of the country that you are working in and local knowledge.
Coneboy
(The Su formula you mentioned uses "Nkt" not "Nk" as a site specific cone factor)
Coneboy,
I have already tried the UBC website, however, can't seem to be able to download if from their server...its suppose to be free..doesn't anyone here have it?
There are a number of commercial software packages available to aid in interpretation of CPT. A useful link can be found at the Georgia Tech web site (
