In the period between September 2010 and December 2011, Christchurch was shaken by a series of strong
earthquakes including the MW7.1 4 September 2010, Mw 6.2 22 February 2011, MW6.2 13 June 2011 and MW6.0
23 December 2011 earthquakes. These earthquakes produced very strong ground motions throughout the city
and surrounding areas that resulted in soil liquefaction and lateral spreading causing substantial damage to
buildings, infrastructure and the community. The stopbank network along the Kaiapoi and Avon River suffered
extensive damage with repairs projected to take several years to complete. This presented an opportunity to
undertake a case-study on a regional scale of the effects of liquefaction on a stopbank system. Ultimately, this
information can be used to determine simple performance-based concepts that can be applied in practice to
improve the resilience of river protection works.
The research presented in this thesis draws from data collected following the 4th September 2010 and 22nd
February 2011 earthquakes. The stopbank damage is categorised into seven key deformation modes that were
interpreted from aerial photographs, consultant reports, damage photographs and site visits. Each deformation
mode provides an assessment of the observed mechanism of failure behind liquefaction-induced stopbank
damage and the factors that influence a particular style of deformation.
The deformation modes have been used to create a severity classification for the whole stopbank system, being
‘no or low damage’ and ‘major or severe damage’, in order to discriminate the indicators and factors that
contribute to ‘major to severe damage’ from the factors that contribute to all levels of damage a number of
calculated, land damage, stopbank damage and geomorphological parameters were analysed and compared at
178 locations along the Kaiapoi and Avon River stopbank systems.
A critical liquefiable layer was present at every location with relatively consistent geotechnical parameters (cone
resistance (qc), soil behaviour type (Ic) and Factor of Safety (FoS)) across the study site. In 95% of the cases the
critical layer occurred within two times the Height of the Free Face (HFF,). A statistical analysis of the
geotechnical factors relating to the critical layer was undertaken in order to find correlations between specific
deformation modes and geotechnical factors. It was found that each individual deformation mode involves a
complex interplay of factors that are difficult to represent through correlative analysis.
There was, however, sufficient data to derive the key factors that have affected the severity of deformation. It
was concluded that stopbank damage is directly related to the presence of liquefaction in the ground materials
beneath the stopbanks, but is not critical in determining the type or severity of damage, instead it is merely the
triggering mechanism. Once liquefaction is triggered it is the gravity-induced deformation that causes the
damage rather than the shaking duration.
Lateral spreading and specifically the depositional setting was found to be the key aspect in determining the
severity and type of deformation along the stopbank system. The presence or absence of abandoned or old river
channels and point bar deposits was found to significantly influence the severity and type of deformation. A
review of digital elevation models and old maps along the Kaiapoi River found that all of the ‘major to severe’
damage observed occurred within or directly adjacent to an abandoned river channel. Whilst a review of the
geomorphology along the Avon River showed that every location within a point bar deposit suffered some form
of damage, due to the depositional environment creating a deposit highly susceptible to liquefaction.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/8743 |
| Date | January 2013 |
| Creators | Bainbridge, Sophie Elizabeth |
| Publisher | University of Canterbury. Geological Sciences |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Sophie Elizabeth Bainbridge, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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