Model Studies of Rapid Driving of Piles Into Permafrost

Abstract

A comprehensive study was made of rapid pile driving into permafrost. This paper is limited to a discussion of flat-tipped model piles penetrating artificial permafrost under the influence of their kinetic energies alone. The first part of the paper is a study of the penetrations of thin, hollow, circular piles as a function of their masses and impact velocities. Experimental results show that, within the range of velocities explored [40 to 500 ft/sec], three types of resisting forces are predominant during penetration. These forces are: crushing, drag and frictional. A model of penetration was developed on the basis of these three forces. The law of penetrati'on, expressed by an empirical equation derived from experimental results, was explainable by the simultaneous existence of these three forces. The second part of the paper is a study of the penetrations of cross-shaped, solid-and hollow-circular, rectangUlar, and square piles as a fUnction Of their shapes. An effective cross section was defined which permitted reduction to a common level of the penetrations of piles having the same mass and impaci velocity. The effective cross section was defined as a function of the perimeter and a reduced thickness of the cross section of the piles Distinctions were made between thick and thin piles. As a corollary of this investigation, the results of a series of field tests conducted in Alaska are presented.