Geotechnical Earthquake Engineering

Geotechnical Earthquake Engineering - 25 Geotechnical...

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© 2003 by CRC Press LLC 25 Geotechnical Earthquake Engineering 25.1 Introduction 25.2 Earthquake Strong Shaking 25.3 Site-Specific Amplification Illustrative Site Response Problem 25.4 Soil Liquefaction Illustrative Soil Liquefaction Problem 25.5 Seismic Slope Stability 25.6 Summary 25.1 Introduction Geotechnical factors often exert a major influence on damage patterns and loss of life in earthquake events. For example, the localized patterns of heavy damage during the 1985 Mexico City and 1989 Loma Prieta, California, earthquakes provide grave illustrations of the importance of understanding the seismic response of deep clay deposits and loose, saturated sand deposits. The near failure of the Lower San Fernando dam in 1971 due to liquefaction of the upstream shell materials is another grave reminder that we must strive to understand the seismic response of critical earth structures. The characteristics and distribution of earth materials at a project site significantly influence the characteristics of the earthquake ground motions, and hence significantly influence the seismic response of the constructed facilities at a site. Moreover, the composition and geometry of earth structures, such as earth dams and solid waste landfills, significantly affect their seismic response. Geotechnical considerations therefore play an integral role in the development of sound earthquake-resistant designs. In this chapter, geotechnical earthquake engineering phenomena such as site-specific amplification, soil liquefaction, and seismic slope stability are discussed. Case histories are used to illustrate how earthquakes affect engineered systems, and estab- lished, simplified empirical procedures that assist engineers in assessing the effects of these phenomena are presented. The field of earthquake engineering is quite complex, so the need for exercising engineering judgment based on appropriate experience is emphasized. 25.2 Earthquake Strong Shaking The development and transmission of earthquake energy through the underlying geology is quite com- plex, and a site-specific seismic response study requires an assessment of the primary factors influencing the ground motion characteristics at a site. They are • Earthquake source mechanism •Travel path geology Jonathan D. Bray University of California at Berkeley
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•Topographic effects • Earthquake magnitude •Distance from zone of energy release •Local soil conditions Earthquakes are produced in a particular geologic setting due to specific physical processes. A midplate earthquake (e.g., New Madrid) will differ from a plate margin earthquake (e.g., San Andreas) [see Nuttli, 1982]. The principal descriptive qualities of the earthquake source are the type of fault displacement (strike-slip, normal, or reverse), depth of the rupture, length of the rupture, and duration of the rupturing.
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Geotechnical Earthquake Engineering - 25 Geotechnical...

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