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(II)

In the present paper, following informations on the vibration of ground and structures are obtained, through the experimental data on free dropping of a weight and through the data measured on three different spots of construction where a Diesel pile hammer drives a pile into the ground.
(1) The empirical equation α = <cr>^<-a> is obtaind on the distance r from the center of shock and the maximum amplitude of ground acceleration α, where the constants c and a have different values according to the direction of the vibration and the natures of the soil. In general, the value of c is large in the hard soil.
(2) When a pile is drived in by a Diesel pile hammer, two types of ground vibration are resulted, one of which (p-type vibration) has high speed of propagation and the other (S-type vibration) has low.
(3) P-type vibration, a kind of longitudinal and dilatational waves, arises when a pile is driven into the ground by a Diesel hammer, or when a weight is dropped upon a disk or an anvil on the ground, as in the case of a forging machine. Its distinctive features are (a) the speed of propagation is high, (b) the amplitude in the vertical direction is larger than that in the horizontal direction. Its freqnency and duration time are large or small according to circumstances.
(4) S-type vibration, a kind of transverse and distortional waves, is caused when a pile and some amount of earth moving with it vibrate as one mass. This type of vibration does not grow in the case of dropping a weight on a disk or an anvil. The special features of this vibration are (a) small speed of propagation and(b) large amplitude in the horizontal direction. The frequency is rather small and the amplitude is large and the duration time is rather long, owing to a large moving mass. This type of vibration may damage houses and structures.
(5) Remarkable forced vibration occurs in a structure when a large shock acceleration is input to it. On the contrary, remarkable free vibration occurs when a small shock, acceleration is input to it.
(6) The model of the ground structure vibrating system, which has been proposed and simulated by an analog computer in our previous paper, agrees tolerably with the actual vibrating system.