Residential Rebuild on TC3 Land

This Christchurch residential site was heavily affected by the Canterbury Earthquake Sequence, with significant liquefaction-related land damage, more than 100 mm of floor level variation across the dwelling, and extensive cracking to the foundation and building. A rebuild was required.

The site presented challenges typical of TC3 land, including high liquefaction susceptibility, shallow groundwater and soft soils at shallow depth. The client wanted a replacement foundation solution that would improve resilience in future earthquakes while retaining a timber floor to match the feel of the original home.

Cook Costello provided the geotechnical and structural engineering input needed to develop a buildable solution suited to the site. Our work included:

• Ground investigations to define the subsurface profile and assess liquefaction and soft soil hazards

• Design of shallow ground improvement measures to help mitigate the effects of liquefaction and soft near-surface soils

• Structural analysis and design of a timber floor foundation system tailored to the site conditions

• Construction support and site involvement to help manage installation risks and confirm the works aligned with the design intent

The result was a code-compliant foundation solution suited to the site, the client’s preference for a timber floor, and the realities of building on TC3 land. By combining shallow ground improvement with a timber floor system, the rebuilt home is better able to tolerate future liquefaction-related movement. Importantly, the foundation was also designed so the home could be re-levelled more easily if significant earthquake movement occurs again.