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INFLUENCE OF UNDERGROUND CAVITY ON THE SEISMICRESPONSE OF U-SHAPED CANYON USING BEM

A 2D scattering and diffraction of plane P and SV waves induced by a U-shaped canyon above underground cavities is proposed herein to account for the topographic effect of such a canyon. Time domain boundary element method(BEM),were performed to study the behaviour of this problem. To show the interaction between U-shaped canyons and underground cavities and their effects on the surface ground motion, a parametric analysis is carried out in very long periodic bands.Influence of various parameters has been investigated. It is shown that site geometry, wave characteristics, and cavity location are the key parameters governing the canyon’s response. In this regard, the important parameters considered in this study are: the width of the underground cavities; the cavity depth; radios of cavity and shape of canyon. INTRODUCTION Recent destructive earthquakes have shown significant evidences of the effects of surface geology and topography on ground motion characteristics at a site. So, explorating of thewave scattering and seismic amplification problems of natural or artificial subsurface cavities is important in geophysics, seismology and earthquake engineering both in theory and practical application.Also, with rapid development of cities, utilization of underground spaces becomes the very important factor affecting the sustainable development of urban society. When an underground space is excavated, it inevitably causes strong ground motions, which may cause serious damage to adjacent structures. The experiences of pastearthquakes as well as analytical, experimentaland numerical studies have disclosed considerable effects of underground cavities or holes like natural karstic cavities, subway and tunnels on the seismic ground response. On the other hand, it is completely evident that the geometry and topography of sites have a significant effect on the seismic ground response and distribution of damages due to earthquakes. The most of cities, dams and bridges are located on canyon shaped topographic features ( Sanchez-Sesma, 1987; Gazetas and Dakoulas,1992; Aviles and Perez-Rocha, 1998). Extensive parametrical studies are done to discriminate the topographical and geotechnical effects on seismic ground amplifications in 2D irregular configurations. Also, most of existent studies concentrated separately on the seismic behavior of topographic features and buried engineering structures and studies about seismic interaction between topography especially canyons and underground cavity have seldom been published.