Co-Seismic Slope Displacements; A Comparative Case Study

Estimation of co-seismic slope displacements remains an area of discussion and uncertainty in geotechnical design. While there are several available methods, with varying applicability to site conditions and design scenarios, it is relatively commonplace within New Zealand engineering practice for the same three methods to be used for legacy reasons, namely the rigid block methods described by Ambraseys & Srbulov (1995), Jibson (2007), and Bray & Travasarou (2007). The objective of this paper is to discuss the importance of applying the right analysis method for the site conditions. An assessment of the most appropriate co-seismic displacement method at three bridge sites was carried out, with a different method ultimately used for each. At Site 1 a simplified Newmark-type displacement method was deemed appropriate. For Site 2, a coupled analysis using selected time history records was used due to the slope height and depth of predicted failure surfaces from pseudo-static analyses. For Site 3, Newmark displacement methods were not considered appropriate due to the presence of deep liquefiable deposits. As a result, finite element analyses were used to better estimate potential seismic displacements.