コンクリート杭の打込みによる地盤ならびに構造物の振動

Ground vibration produced by driving in a reinforced concrete pile, as in construction jobs, is of importance because of damage which may be caused to structures, and of annoyance which may be suffered by the public. In this paper, some characters of such transient ground- and structure-motions are presented. Ground-and structure-acceleration-time curves for Diesel pile hammer excitation and their frequency spectra have revealed the following two.
(1) Ground motions in the near vicinity of the hammer contain a large number of frequency components, but have no remarkable dominant-frequency components.
(2) Within a distance of 70m from the hammer, the amplitude of ground acceleration, especially high frequency component of it, are damped down and the dominant frequency component of 5-8 Hz is observed with increasing distance.
A simple model simulated by an analog computer is proposed to represent ground- and structure-motions. And according to the analysis with the model, two results are deduced.
(1) Acceleration-time curves obtained by the model, are somewhat similar to that of ground- and structure-motions.
(2) The acceleration amplification coefficient of a structure becomes large, when the dominant frequency of the interior ground approaches to the natural frequency of the structure, especially when the mass of the structure is much smaller than that of the interior ground.