BPT for Soil Characterisation

[ONENGINEER]

The soil during initial site investigation contains some loose gravelly sand materials with trace cobbles.

Becker Penetration Testing has been proposed for the next stage of SI instead of SPT. The object is to find soil parameters and liquefaction assessment. Would appreciate feedback on pros and cons of the close and open ended BPT.

 

[dgillette]

There are two different correlations for estimating equivalent SPT N60 from closed-bit BPT. One is by Les Harder and H. Bolton Seed at Berkeley, approx. 1988. It uses the bounce-chamber pressure in the LinkBelt / ICE diesel hammer to adjust the blowcount for driving energy. The other is by Alex Sy and Dick Campanella at U. British Columbia, approx. 1991. It uses Pile Dynamics Inc. pile-driving analyzer for measurement of energy, and wave-equation analysis to calculate rod friction so the driving resistance can be separated into the tip resistance and the rod friction. A little Googling will find the references for you I'm sure.

Open-bit BPT testing has been tried, but was found to give very inconsistent results, possibly due to alternate plugging and clearing of the bit. You can sample with open-bit Becker with compressed air, but all you get is cuttings collected in a cyclone.

Production is fairly rapid since the rods don't have to trip in and out like with a SPT sampler.