WAVE-PROPAGATION IMPEDIMENT IN A STRATUM AND WAVE IMPEDING BLOCK (WIB) MEASURED FOR SSI RESPONSE REDUCTION

This paper investigates a soil-structure interaction system with due attention to wave propagation in soil and the impediment effect of a stratum depth when a rigid base is assumed. The physical insight into the response feature across the cutoff frequency is first demonstrated analytically by taking an out-of-plane harmonic motion of a stratum under an imposed surface strip loading. The time-domain boundary element method is then utilized for the in-plane motion of a soil-rigid foundation interaction when impulse loading is imposed on the foundation. The Ricker wave type loading of various predominant periods is chosen to clarify the wave motion as propagating or impeded in relation to the stratum depth; or equivalently the period ratio between loading and the fundamental period of the stratum is best chosen for a parameter for the investigation. Furthermore, the response reduction measure is proved for an installed stiff obstacle, a wave impeding block (WIB), below the foundation at an appropriate depth from an active use of the cutoff frequency criterion of a soil stratum.