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Research papers, University of Canterbury Library

Advanced seismic effective-stress analysis is used to scrutinize the liquefaction performance of 55 well-documented case-history sites from Christchurch. The performance of these sites during the 2010-2011 Canterbury earthquake sequence varied significantly, from no liquefaction manifestation at the ground surface (in any of the major events) to severe liquefaction manifestation in multiple events. For the majority of the 55 sites, the simplified liquefaction evaluation procedures, which are conventionally used in engineering practice, could not explain these dramatic differences in the manifestation. Detailed geotechnical characterization and subsequent examination of the soil profile characteristics of the 55 sites identified some similarities but also important differences between sites that manifested liquefaction in the two major events of the sequence (YY-sites) and sites that did not manifest liquefaction in either event (NN-sites). In particular, while the YY-sites and NN-sites are shown to have practically identical critical layer characteristics, they have significant differences with regard to their deposit characteristics including the thickness and vertical continuity of their critical zones and liquefiable materials. A CPT-based effective stress analysis procedure is developed and implemented for the analyses of the 55 case history sites. Key features of this procedure are that, on the one hand, it can be fully automated in a programming environment and, on the other hand, it is directly equivalent (in the definition of cyclic resistance and required input data) to the CPT-based simplified liquefaction evaluation procedures. These features facilitate significantly the application of effective-stress analysis for simple 1D free-field soil-column problems and also provide a basis for rigorous comparisons of the outcomes of effective-stress analyses and simplified procedures. Input motions for the analyses are derived using selected (reference) recordings from the two major events of the 2010-2011 Canterbury earthquake sequence. A step-by-step procedure for the selection of representative reference motions for each site and their subsequent treatment (i.e. deconvolution and scaling) is presented. The focus of the proposed procedure is to address key aspects of spatial variability of ground motion in the near-source region of an earthquake including extended-source effects, path effects, and variation in the deeper regional geology.

Images, UC QuakeStudies

University of Canterbury Vice-Chancellor Rod Carr conferring with former Chancellor Rex Williams, inside the UCSA's "Big Top" tent. The tent was erected in the UCSA car park to provide support for students in the aftermath of the 22 February 2011 earthquake. Around them students have gathered to watch a local musician play. The student have spent the day clearing liquefaction from Christchurch properties as part of the Student Volunteer Army.

Images, UC QuakeStudies

The ruins of the historic Durham Street Methodist Church in the aftermath of the 22 February 2011 earthquake. The only parts of the building still upright are those supported by steel braces placed there after the 4 September 2010 earthquake to strengthen the building as it awaited repairs. Rubble has spilled out onto the street, knocking over the safety fences that were also erected after September. Silt from liquefaction has covered the road around the church.

Images, UC QuakeStudies

The ruins of the historic Durham Street Methodist Church in the aftermath of the 22 February 2011 earthquake. The only parts of the building still upright are those supported by steel braces placed there after the 4 September 2010 earthquake to strengthen the building as it awaited repairs. Rubble has spilled out onto the street, knocking over the safety fences that were also erected after September. Silt from liquefaction has covered the road around the church.

Images, UC QuakeStudies

The ruins of the historic Durham Street Methodist Church in the aftermath of the 22 February 2011 earthquake. The only parts of the building still upright are those supported by steel braces placed there after the 4 September 2010 earthquake to strengthen the building as it awaited repairs. Rubble has spilled out onto the street, knocking over the safety fences that were also erected after September. Silt from liquefaction has covered the road around the church.

Images, UC QuakeStudies

University of Canterbury Vice-Chancellor Rod Carr addressing a local musician inside the UCSA's "Big Top" tent. The tent was erected in the UCSA car park to provide support for students in the aftermath of the 22 February 2011 earthquake. The audience is made up of students who have spent the day clearing liquefaction from Christchurch properties as part of the Student Volunteer Army.

Images, UC QuakeStudies

A two-storey house in Avonside Drive with a warped upper balcony. The photographer comments, "This house is on Avonside Drive opposite the Avon River. The land in this area spread laterally and had bad liquefaction of the soil. This caused some houses to sink into the ground, but as the balcony supports did not sink as much the balcony came to rest at a crazy angle".

Images, UC QuakeStudies

Workers operate a drilling rig, sampling soil as part of EQC's geotechnical investigation of TC3 land. The photographer comments, "The work of getting 'soil' samples from all the areas marked as green/blue zones in Christchurch. These areas may be susceptible to liquefaction if a major earthquake occurs. The soil samples were a failure as all they found was sand".

Research papers, University of Canterbury Library

The paper presents preliminary findings from comprehensive research studies on the liquefaction-induced damage to buildings and infrastructure in Christchurch during the 2010-2011 Canterbury earthquakes. It identifies key factors and mechanisms of damage to road bridges, shallow foundations of CBD buildings and buried pipelines, and highlights the implications of the findings for the seismic analysis and design of these structures.

Images, eqnz.chch.2010

Our House - Liquefaction (22.02.2011) Woolston Christchurch Canterbury New Zealand © 2011 Phil Le Cren Photo Taken With: Canon EOS 1000D + Canon EF/EF-S lenses + 10.1 effective megapixels + 2.5-inch TFT color LCD monitor + Eye-level pentamirror SLR + Live View shooting. + EOS Built-in Sensor cleaning system + Wide-a...

Research papers, University of Canterbury Library

Using case studies from the 2010-2011 Canterbury, New Zealand earthquake sequence, this study assesses the accuracies of paleoliquefaction back-analysis methods and explores the challenges, techniques, and uncertainties associated with their application. While liquefaction-based back-analyses have been widely used to estimate the magnitudes of paleoearthquakes, their uncertain efficacies continue to significantly affect the computed seismic hazard in regions where they are relied upon. Accordingly, their performance is evaluated herein using liquefaction data from modern earthquakes with known magnitudes. It is shown that when the earthquake source location and mechanism are known, back-analysis methods are capable of accurately deriving seismic parameters from liquefaction evidence. However, because the source location and mechanism are often unknown in paleoseismic studies, and because accurate interpretation is shown to be more difficult in such cases, new analysis techniques are proposed herein. An objective parameter is proposed to geospatially assess the likelihood of any provisional source location, enabling an analyst to more accurately estimate the magnitude of a liquefaction-inducing paleoearthquake. This study demonstrates the application of back-analysis methods, provides insight into their potential accuracies, and provides a framework for performing paleoliquefaction analyses worldwide.