# TC1, TC2, TC3, the ground, graded

The red zone answered whether a suburb could stay; for the land that stayed, the 2011 grading answered what the ground asks of the foundations. 9,603 hectares of flat residential Christchurch in 296 mapped areas.

## The grades

- **TC1**, Technical Category 1, Grey. Future land damage from liquefaction is unlikely. Standard foundations for concrete slabs and timber floors acceptable. Minor additional foundation works may be required eg more reinforcing 1,651 ha in 29 areas.
- **TC2**, Technical Category 2, Yellow. Minor to moderate land damage from liquefaction is possible in future significant earthquakes. Standard timber piled foundations or enhanced concrete foundations 5,768 ha in 157 areas.
- **TC3**, Technical Category 3, Blue. Moderate to significant land damage from liquefaction is possible in future significant earthquakes. Site-specific geotechnical investigation and specific engineering foundation design required eg deep pile foundations, innovative ground strengthening, etc 2,185 ha in 110 areas.

## Also in the earthquakes

- [The sequence](https://www.chch.live/sequence), every shake since 2010, counted
- [Earthquakes, live](https://www.chch.live/quakes), the ones that just landed
- [The faults](https://www.chch.live/faults), the traces under the plains
- [Liquefaction](https://www.chch.live/liquefaction), the ground that moved
- [The red zone](https://www.chch.live/redzone), the land the Crown wrote off
- [The rebuild’s receipts](https://www.chch.live/rebuild), SCIRT’s photograph archive
- [The earthquakes, explained](https://www.chch.live/how-nz-works/canterbury-earthquakes), what happened and why
- [Liquefaction, explained](https://www.chch.live/how-nz-works/liquefaction), why the east failed
- [The rebuild, explained](https://www.chch.live/how-nz-works/rebuild), the machinery that put it back

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Christchurch City Council open data: QuakeFoundationDesign, the CERA technical categories of 2011, simplified 30 m. A category is a 2011 engineering verdict for a patch of ground, not a finding about any one address. The line under the worst of it: https://www.chch.live/redzone; the ground: https://www.chch.live/liquefaction. The files: https://www.chch.live/technical-categories.json · https://www.chch.live/technical-categories.geojson