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Research papers, University of Canterbury Library

The focus of the study presented herein is an assessment of the relative efficacy of recent Cone Penetration Test (CPT) and small strain shear wave velocity (Vs) based variants of the simplified procedure. Towards this end Receiver Operating Characteristic (ROC) analyses were performed on the CPT- and Vs-based procedures using the field case history databases from which the respective procedures were developed. The ROC analyses show that Factors of Safety (FS) against liquefaction computed using the most recent Vs-based simplified procedure is better able to separate the “liquefaction” from the “no liquefaction” case histories in the Vs liquefaction database than the CPT-based procedure is able to separate the “liquefaction” from the “no liquefaction” case histories in the CPT liquefaction database. However, this finding somewhat contradicts the assessed predictive capabilities of the CPT- and Vs-based procedures as quantified using select, high quality liquefaction case histories from the 20102011 Canterbury, New Zealand, Earthquake Sequence (CES), wherein the CPT-based procedure was found to yield more accurate predictions. The dichotomy of these findings may result from the fact that different liquefaction field case history databases were used in the respective ROC analyses for Vs and CPT, while the same case histories were used to evaluate both the CPT- and Vs-based procedures.

Images, UC QuakeStudies

Dried liquefaction in North New Brighton. The photographer comments, "This shape formed as the liquefaction after the 23 December earthquake in Christchurch started to dry out".

Images, UC QuakeStudies

Liquefaction in North New Brighton. The photographer comments, "This was the liquefaction pouring out of a split in the road where it joins the side-walk. The quakes felt pretty violent, but the damage was less severe than the February one. Unlucky for me the epicentre was only 9.6km away and smaller aftershocks were a lot closer".

Articles, UC QuakeStudies

The Christchurch liquefaction study was initiated to better determine liquefaction susceptibility in Christchurch city. It aimed to improve on earlier liquefaction susceptibility maps, which were based on soil type and distribution, by incorporating soil strength data into liquefaction analysis. This stage of the study included collating available geological and geotechnical data from Environment Canterbury and Christchurch City Council into a database, modelling liquefaction hazard and ground damage and presenting these as maps. The report contains many recommendations, which were taken up in subsequent stages of the study. (Note that the results of Stage 1 of the Christchurch liquefaction study were provided to Environment Canterbury as a letter rather than a report. This was a summary of work completed to 30 June 2001, including a review of geological and geotechnical data available within Environment Canterbury and Christchurch City Council records.) See Object Overview for background and usage information.

Research papers, University of Canterbury Library

The city of Christchurch and its surrounds experienced widespread damage due to soil liquefaction induced by seismic shaking during the Canterbury earthquake sequence that began in September 2010 with the Mw7.1 Darfield earthquake. Prior to the start of this sequence, the city had a large network of strong motion stations (SMSs) installed, which were able to record a vast database of strong ground motions. This paper uses this database of strong ground motion recordings, observations of liquefaction manifestation at the ground surface, and data from a recently completed extensive geotechnical site investigation program at each SMS to assess a range of liquefaction evaluation procedures at the four SMSs in the Christchurch Central Business District (CBD). In general, the characteristics of the accelerograms recorded at each SMS correlated well with the liquefaction evaluation procedures, with low liquefaction factors of safety predicted at sites with clear liquefaction identifiers in the ground motions. However, at sites that likely liquefied at depth (as indicated by evaluation procedures and/or inferred from the characteristics of the recorded surface accelerograms), the presence of a non-liquefiable crust layer at many of the SMS locations prevented the manifestation of any surface effects. Because of this, there was not a good correlation between surface manifestation and two surface manifestation indices, the Liquefaction Potential Index (LPI) and the Liquefaction Severity Number (LSN).

Research papers, University of Canterbury Library

The 2010–2011 Canterbury earthquake sequence began with the 4 September 2010, Mw7.1 Darfield earthquake and includes up to ten events that induced liquefaction. Most notably, widespread liquefaction was induced by the Darfield and Mw6.2 Christchurch earthquakes. The combination of well-documented liquefaction response during multiple events, densely recorded ground motions for the events, and detailed subsurface characterization provides an unprecedented opportunity to add well-documented case histories to the liquefaction database. This paper presents and applies 50 high-quality cone penetration test (CPT) liquefaction case histories to evaluate three commonly used, deterministic, CPT-based simplified liquefaction evaluation procedures. While all the procedures predicted the majority of the cases correctly, the procedure proposed by Idriss and Boulanger (2008) results in the lowest error index for the case histories analyzed, thus indicating better predictions of the observed liquefaction response.

Images, UC QuakeStudies

A van partially submerged in liquefaction. The photographer comments, "A van that unluckily drove into a hole caused by the terrible liquefaction on Beach Road, North New Brighton during the Christchurch earthquake".

Images, UC QuakeStudies

A 'sand volcano' of liquefaction silt in Bexley. The photographer comments, "Liquefaction is just a mixture of sand and water squeezed up from the ground, but with a little imagination it has a beauty in its untouched state".

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "I found this face amongst the liquefaction. It is like one of them diagrams where they segment different parts of the brain depending on their functions".

Images, UC QuakeStudies

A van partially submerged in liquefaction. The photographer comments, "A van that unluckily drove into a hole caused by the terrible liquefaction on Beach Road, North New Brighton during the Christchurch earthquake".

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "The liquefaction after the 23 December earthquake in Christchurch started to dry out and the thicker deposits started to curl up like broken drain pipe".

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "The day before this was liquefaction pouring out of the ground, but within a day it has dried up and will soon turn into a gritty dust".

Images, UC QuakeStudies

Liquefaction and flooding in Waitaki Street, Bexley. The photographer comments, "Waitaki Street a week after the Christchurch Earthquake. Because of the damage to the drains and liquefaction in the area the streets are not drying out".

Research papers, University of Canterbury Library

Recurrent liquefaction in Christchurch during the 2010-2011 Canterbury earthquake sequence created a wealth of shallow subsurface intrusions with geometries and orientations governed by (1) strong ground motion severity and duration, and (2) intrinsic site characteristics including liquefaction susceptibility, lateral spreading severity, geomorphic setting, host sediment heterogeneity, and anthropogenic soil modifications. We present a suite of case studies that demonstrate how each of these characteristics influenced the geologic expressions of contemporary liquefaction in the shallow subsurface. We compare contemporary features with paleo-features to show how geologic investigations of recurrent liquefaction can provide novel insights into the shaking characteristics of modern and paleo-earthquakes, the influence of geomorphology on liquefaction vulnerability, and the possible controls of anthropogenic activity on the geologic record. We conclude that (a) sites of paleo-liquefaction in the last 1000-2000 years corresponded with most severe liquefaction during the Canterbury earthquake sequence, (b) less vulnerable sites that only liquefied in the strongest and most proximal contemporary earthquakes are unlikely to have liquefied in the last 1000-2000 years or more, (c) proximal strong earthquakes with large vertical accelerations favoured sill formation at some locations, (d) contemporary liquefaction was more severe than paleoliquefaction at all study sites, and (e) stratigraphic records of successive dike formation were more complete at sites with severe lateral spreading, (f) anthropogenic fill suppressed surface liquefaction features and altered subsurface liquefaction architecture.

Images, UC QuakeStudies

Dried liquefaction silt in North New Brighton. The photographer comments, "This is the the top layer of liquefaction that has dried up in the hot sun. A broken eggshell is around 5 times stronger than these, but a fallen leaf is just not enough to break one. You can see underneath that the heavier sandy layer of liquefaction has dried and has cracked as well".