Seismic Ratings for Degrading Structural Systems
205 GEOTECHNICAL ASPECTS OF THE 22 FEBRUARY 2011 CHRISTCHURCH EARTHQUAKE Misko Cubrinovski1, Brendon Bradley1, Liam Wotherspoon2, Russell Green3, Jonathan Bray4, Clint Wood5, Michael Pender2, 6 7 8 1 John Allen , Aaron Bradshaw , Glenn Rix , Merrick Taylor , Kelly Robinson1, Duncan Henderson1, Simona Giorgini1, Kun Ma1, Anna Winkley1, Josh Zupan4, Thomas O’Rourke9, 10 11 Greg DePascale , Donnald Wells SUMMARY The 22 February 2011, Mw6.2-6.3 Christchurch earthquake is the most costly earthquake to affect New Zealand, causing 181 fatalities and severely damaging thousands of residential and commercial buildings, and most of the city lifelines and infrastructure. This manuscript presents an overview of observed geotechnical aspects of this earthquake as well as some of the completed and on-going research investigations. A unique aspect, which is particularly emphasized, is the severity and spatial extent of liquefaction occurring in native soils. Overall, both the spatial extent and severity of liquefaction in the city was greater than in the preceding 4th September 2010 Darfield earthquake, including numerous areas that liquefied in both events. Liquefaction and lateral spreading, variable over both large and short spatial scales, affected commercial structures in the Central Business District (CBD) in a variety of ways including: total and differential settlements and tilting; punching settlements of structures with shallow foundations; differential movements of components of complex structures; and interaction of adjacent structures via common foundation soils. Liquefaction was most severe in residential areas located to the east of the CBD as a result of stronger ground shaking due to the proximity to the causative fault, a high water table approximately 1m from the surface, and soils with composition and states of high susceptibility and potential for liquefaction.
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