Analysis of Soil Penetration by a Whirl-Excited Probe

Abstract

The vertical penetration of sedimentary materials is of importance for many scientific and engineering purposes, including soil sampling and pile driving. One approach to this problem is to achieve orbital motion of a probe in a horizontal plane, thereby displacing the soil radially, with excitation produced by a rotating unbalance. The probe thus reacts with the soil, resulting in radial and tangential forces. The former produce hole enlargement, and the latter are in the nature of frictional drag related to orbital motion. The analysis indicates that such a system is bistable, with radial probe amplitudes dependent upon whirl frequency, soil friction, soil compressive resistance, probe mass, and exciter unbalance. Such a device exhibits several desirable operational characteristics, tending to enlarge the hole at increased radial resistance, and to decrease amplitude at reduced resistance, thus being somewhat self-regulating. A prototype has been built and tested experimentally; however, this paper is primarily a study of the steady-state vibratory behavior of a whirl-excited probe, with basic design equations presented.