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PROBABILISTIC SIMPLIFIED SEISMIC
PERFORMANCE ASSESSMENT OF EARTH
SLOPES AND STRUCTURES
Jorge Macedo, Jonathan Bray & Norman Abrahamson
Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA, USA
Thaleia Travasarou
Fugro Consultants Inc., Oakland, CA, USA
ABSTRACT
Recently developed probabilistic simplified procedures to assess the seismic performance of earth structures and natural
slopes are presented. Seismic slope performance is assessed using the frameworks of a Newmark-based method to
estimate the likely amount of seismic displacement and a pseudostatic slope stability procedure that estimates a seismic
pseudostatic coefficient that is dependent on key factors, including the seismic hazard. The proposed procedures are
applied to two sites in the United States.
Under the first framework, the seismic performance assessment is based on the estimation of the displacement hazard
curve which provides the mean annual rate of exceedance of the seismic slope displacement. A methodology is proposed
and implemented for the estimation of the displacement hazard curve. The seismic slope displacement estimates
calculated with the recently developed fully probabilistic procedures are compared with the results from partially
probabilistic methods (e.g., Bray and Travasarou, 2007). Currently employed procedures, such as Bray and Travasarou
(2007), do not provide consistently conservative or unconservative assessments of the seismic slope displacement hazard.
The comparison of the results of the fully and partially probabilistic simplified seismic slope displacement procedures
depends on several factors and in particular on the seismotectonic setting (e.g., shallow crustal earthquakes vs. subduction
zone earthquakes). The fully probabilistic approach is preferred, because it is more rigorous than a partially probabilistic
approach.
Under the second framework, the seismic coefficient used in a pseudostatic slope stability analyses should be a function
of the dynamic properties of the earth system or natural slope, the seismic ground motion characteristics at the site of a
specific project, and the allowable level of seismic displacement (e.g., Bray and Travasarou 2009). Thus, a methodology
for a fully probabilistic based estimation of the seismic coefficient that depends on these factors was developed.
Comparisons of the results of the partially probabilistic procedure proposed by Bray and Travasarou (2009) show
consistent results for the seismic coefficient estimated with the new fully probabilistic procedure. However, the new fully
probabilistic procedure enables the engineer to address directly the target design level and associated uncertainties.
The fully probabilistic seismic slope displacement procedures developed in this study have been implemented as Visual
Basic applications (VBA) in an Excel spreadsheet. The procedures were developed for a wide range of earth structures
and natural slopes for shallow crustal earthquakes and subduction zone earthquakes. They can be readily used in practice
to perform rigorous fully probabilistic performance-based seismic slope stability hazard assessments.
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