Engineers on the Canterbury earthquakes and building earthquake-resilient cities

The Science Media Centre blog has a Q&A session with earthquake engineering specialists.

The topics covered are:

  • What is an earthquake-prone building?
  • How do they vary in terms of factors causing their “prone-ness”?
  • In the wake of the quakes and the current commission, can we expect to see the building code or enforcement changed?
  • What possible areas of the code might be focused on in future review of the legislation?
  • Why does it take so long to analyse a building? What does it involve?
  • What are some of the ways a building which is earthquake prone can be brought up to a higher standard?
  • To what extent will the strong ground motions recorded in the Christchurch earthquakes lead to changes in New Zealand’s building code?
  • Has enough been learned in engineering terms to reduce the damage that liquefaction and lateral spreading does to foundations of structures?
  • And if sea levels rise 2m over the current century, will the higher water table increase the risks of liquefaction in Christchurch or Wellington?
  • Should households pay insurance premiums based on the perceived seismic risk of their site, the anticipated performance of their house design, and the risk that the suburb around them may be abandoned even if their specific house survives?
  • Should homeowners be rebuilding to a standard which will enable their homes to perform much better in the next big quake – such as a major shake on the Alpine Fault – rather than simply suffering exactly the same damage all over again?

The blog is here
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Christchurch Stadium

The Ministry of Economic Development have set up a web page to provide information about the new stadium being constructed in Addington. Key dates will be added as they become known and there is an on-line contact form for questions.

The web page is here.
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Land stability in the inner city – Tonkin & Taylor report

The city council has released Tonkin & Taylor’s interpretative report on the central city (land within the Four Avenues – Fitzgerald, Moorhouse, Deans & Harper, Bealey – but excluding Hagley Park). A copy of the report can be downloaded from here.

The following are from the report’s executive summary:

No areas within the CBD or adjacent commercial areas were identified as having ground conditions that would preclude rebuilding on those sites, although more robust foundation design and/or ground improvement may be required. The risks of lateral spreading adjacent to some sections of the Avon River will require detailed geotechnical assessments, however, the adoption of a minimum 30m set-back required for creation of the Avon River Park will likely preclude the worst affected areas from future development.

Christchurch is not unique in being located on soils susceptible to liquefaction within a seismically active region. There are a number of cities and large urban centres around the world (including Wellington on the North Island), where the level of seismic hazard is similar to or greater than that at Christchurch. Presuming that it is economically feasible to utilise appropriate foundation / ground improvement systems, there are few sites that would be considered unsuitable for development purely on the basis of a liquefaction hazard.

The following are a few extracts from the body of the report. While repeated here out of context, they may help understand the complexity of the geology of parts of the inner city.
It is important to appreciate that, whilst the presence of sand boils is a confirmation that liquefaction has occurred, the absence of sand boils or other ground disturbance does not mean that liquefaction has not occurred beneath the surface. The extensive coverage of land within the central city by large footprint buildings and thick pavements may have prevented significant formation of sand boils. Additionally, there are many locations within the central city where a relatively thick crust of non-liquefiable materials may have prevented surface expression of liquefaction. (pp 46-7)

The change in ground elevation since 04 September 2010 (inferred from the LiDAR data and taking account of likely regional tectonic uplift/subsidence), suggests that ground deformation has occurred in areas where little or no land damage was observed. (p 47)

The analyses indicate that a liquefaction hazard is present across virtually the whole of the CBD and adjoining commercial areas, and is not limited to those locations where liquefaction-induced land damage has been observed (i.e. suggesting that area wide deep liquefaction is likely to have occurred). This observation is considered generally consistent with the LiDAR data which suggests settlement may have occurred in some areas where no land damage has been mapped at the ground surface. (p 51)

It should be recognised that, apart from a few localised areas, the overall impact of liquefaction and lateral spreading on the central city resulting from the recent seismic events, has not been as severe as that which has occurred in many of the eastern suburbs and Kaiapoi. This is considered to be due to a combination of the generally better ground conditions present, greater land coverage from buildings and heavy pavements, lower groundwater levels and more substantial foundations. (p 56)

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Major road works on Woodham Road

Major infrastructure work (sewer renewal) along Woodham Road will begin on Monday morning (14th) and is expected to finish within 4 months. The map below shows the extent of the work that will be done. The first phase starts at Tancred street and heads east. 

From the Infrastructure Rebuild website:

Full traffic management will be in place as detailed below.
  • This work will start Monday 14 November.  We will be working Monday to Friday between the hours of 7am to 5pm, and on Saturdays between the hours of 7am to 3pm. On rare occasions we may have to work on a Sunday to complete essential work.
  • We expect the work to take about four months to complete, subject to favourable weather and on-site conditions.
  • This first phase of works will commence between Gloucester Street and Tancred Street, and extend east to the Ngarimu Street / Woodham Road intersection. 
  • This work will impact on traffic movements.  The following traffic management will be in place:
    • One-way east-bound traffic will be maintained along Woodham Road throughout this phase of the works. Please take care when exiting your property to ensure you travel in the correct direction.
    • Between Gloucester Street and Tancred Street, the west-bound traffic lane along Woodham Road will be closed.  A detour route via Gloucester Street and Linwood Avenue will be sign posted.
    • When the work site is extended east to Ngarimu Street, west-bound traffic will be detoured via Worcester Street, Surrey Street, and Gloucester Street to Linwood Avenue.
    • Provision will be made for parking and access to the doctor’s surgery on the Gloucester Street / Woodham Road intersection.
    • On-street parking will not be available in the vicinity of the works to maintain a safe traffic lane.
    • Full signage will clearly indicate detours.

• An update notice explaining progress with the works towards Avonside Drive, and further traffic detours, will be circulated early in 2012.

 Full details are available on the Infrastructure Rebuild website here.
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TV documentary – Battle at the Basilica

A documentary, called Battle at the Basilica, has been filmed around the post-earthquake work on the Cathedral of the Blessed Sacrament in Barbadoes Street. 

The documentary will be shown on TV One on Sunday the 16th of October at 11.30am.  It is to be shown again on TVNZ 7 on Tuesday the 18th of October at 6pm, and repeated on Wednesday the 19th of October at 12 noon.

More information is available on the Cathedral’s website here. The latest Cathedral update is here.
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