Skin friction from CP Test

[tower2020]

I have cone penetration test results from a delta. The soil consisits of layers of sand, silt and clay (alternating layers of cohesionless and cohesive soils). The results from the test give qt, fs, fr, total stress, effective stress, pore pressure, Cn, N60, N160, undrained shear strength....etc, for the soil layers (all the way down to 25m depth).

My question is, using the cpt results, what is the best method for computing the allowable skin friction on a driven steel pipe pile.

I have found different formulas. Bowles suggests using qc (cone bearing pressure reading) to determine the skin friction. He also lists a formula to calculate the skin friction from the sleeve friction reading. Both these methods seem straightforward, but they give different results.... In addition, when I use the undrained shear strength values (for the cohesive soils) in the lambda method for calculating skin friction, I get much higher values.

Any info would be greatly appreciated.

 

[moe333]

A paper by PK Robertson & R.G. Campanella (1988 Balkema) did a comparison of CPT methods for axial capacity of driven piles. The LCPC method (Bustamante and Gianeselli, 1982) gave the best prediction copared with field tests. This method uses cone friction which is generally more reliable than sleeve friction. TRy doing a google search to find the paper.