"Controls" Pocket Penetrometer

[VikingEngineer]

I am reviewing this handy little instrument and have some questions. The instrument was developed by Ing. Prof. Alberto Bucchi. It has a dial gauge that reads penetration pressure in kilograms. There are an assortment of five tips that may be selected of diameter quarter inch, 10, 15, 20 and 25 mm. The good professor claims that by "back calculating" from Terzaghi's bearing formulae you may calculate the cohesion or undrained shear stress of the soil, having determined the q by dividing the penetration force by the probe area. Some initial readings that I took indicate extremely high values of c, they seem unrealistic at 420 and 180 KPA. I am keen to hear whether anyone has used this instrument and if it is accurate? I have some reservations of applying Terzaghi's bearing formulae to very small probe diameters.

 

[jike]

I have used a pocket penetrometer in the field and I think it is a good tool for determining in place unconfined compressive strength for clay. Make sure you use it on undisturbed soil.

After awhile, you will develop your ability to estimate how strong some clay is without the pentrometer.

 

[oldestguy]

As to the instruments sold in the States by SoilTest and others, with two tips; I have found that they are reasonably accurate for clays up to an unconfined compressive strength of about 2 tons per sq. ft. They read direct, no calcs needed.

These penetrometers are not useful if there is more than about 20 percent sand content.