A FEW STUDIES ON SHEAR STRAINS INDUCED IN SUBSURFACE GROUND SUBJECTED TO BASE-ROCK MOTIONS

Abstract

 Strains induced in subsurface ground during an earthquake are the most influential seismic action upon underground structures such as urban tunnels. This paper discusses about shear strains which are caused by horizontal vibration of subsurface ground, and intends to provide some elementary knowledge about relationship between the strains and wave-form of input base-rock acceleration. First, assuming one-dimensional model of a viscoelastic continuum on rigid base, strains produced by simple base movements which are expressed as an impulsive acceleration and a single-cycle harmonic acceleration wave are analytically formulated. Then parametric studies are conducted with use of the formula to know the essential factors in the base movement that dominate the magnitude of the strains. Finally, a few thinking are made to clarify the relationship between movement velocity of base-rock and the strains induced.