Free-Falling Penetrometers: A Laboratory Investigation in Clay

This paper presents the results of a series of laboratory model free-falling penetrometer (FFP) tests in kaolin clay. A thin-shafted FFP has been allowed to free fall and has also been pushed at a relatively slow constant rate into clay beds. Different configurations are used to examine the influences of various properties (FFP mass, tip diameter, tip shape, impact velocity, and clay-bed strength) on the rate effects in FFP tests. The rate effects are determined by comparing the dynamic and static penetration resistances measured from the free-fall and constant rate of penetration tests. The rate effects are found to be independent of the FFP mass, tip shape, and tip diameter but are influenced by the clay-bed strength and FFP velocity.