Housing New Zealand identifies TC2/TC3 foundation trial sites

Housing New Zealand’s earthquake recovery manager Andrew Booker said 32 Corporation properties had been identified in Aranui, Bryndwr, Bishopdale, Parklands, South New Brighton, Burwood, Avondale and Mairehau.

Five of the properties are zoned TC2 with ‘type B’ dwelling foundations (timber piles and concrete ring foundations), 13 are ‘type B’ on TC3 land and 14 are ‘type C’ (concrete slab foundations) also on TC3 land.

After site visits and discussions with the partners involved in the trials, the selection was narrowed down to five ‘type B’ dwellings on TC2 land, six on TC3 and nine on ‘type C’ TC3 land.  The selection was based on structural engineers’ input and geotechnical evaluation reports.

Housing New Zealand is partnering with Southern Response, the Ministry of Innovation, Building and Employment’s Engineering Advisory Group, and Arrow International on the collaborative pilot programme.

Mr Booker said the group had engaged three geotechnical firms – Golders, Geoscience and Tonkin & Taylor as well as structural engineers  Lewis Bradford and Powell Fenwick.

‘We need to ensure we have high quality professional expertise assisting us with this work,’ he said.  ‘The houses that have been identified on our properties are single storeyed buildings, one double-storey house and adjoining flats.  They are mainly brick buildings with concrete tile roofs.  Houses like these are common in Canterbury and the roofs are very heavy - up to 12 tonnes of tiles.’

‘The engineers will be fully occupied before Christmas with the property assessments.  Some sites need only shallow investigation (down to four metres depth) and others need deeper investigation down to 15-18 metres which will require heavy-duty equipment.’

‘In the new year, every property will be thoroughly examined with further analysis inside and underneath the house and the re-levelling work required. Discussions have already taken place with the contractors who will be undertaking the building and re-levelling work.  We are also looking at what products are available and how they can be used to best undertake repairs.’

Mr Booker said the project wasn’t about land remediation.  It was all to do with how houses could be repaired on land that had been zoned TC2 and TC3.  Results would be publicly available as they were completed and the building and construction sector would be advised of the work programme as it developed.

Definitions

• TC2  - minor land deformations possible in a future small to medium sized earthquake, and up to moderate land deformations in a future moderate to large earthquake.
• TC3 – moderate land deformations possible in a future small to medium sized earthquake, and significant land deformations in a future moderate to large earthquake.
• TC2/TC3 definition: Interim guidance for repairing and rebuilding foundations in Technical Category 3: Appendix C. Published by Building & Housing Group (MBIE) 27 April 2012.