Brian Perry Civil

CATEGORY 2: Projects with a value of between $5 million and $20 million

PROJECT: Christchurch Town Hall Conservation. CONTRACTOR: Brian Perry Civil

An inside job

As a result of the 2010/11 Canterbury earthquakes, the highly and acoustically acclaimed Christchurch Town Hall sank 300mm and rotated 600mm laterally towards the adjacent Avon River.

While the building itself held up comparatively well, lateral spread of the ground towards the river and liquefaction undermined the foundations.

Jet grouting was identified as the best solution to address the issue and to stabilise and mitigate further movement. The remedial work, including the complete renovation and strengthening of the building itself and the surrounding exterior patios etc was awarded to Hawkins Construction, which subcontracted the grouting work to Brian Perry Civil and Keller Ground Engineering in a joint venture (JV) contract. Geotechnical consultants Tonkin & Taylor were responsible for concept design and specifying performance requirements, with the JV responsible for construction design, column layout and physical works.

The upmost in careful detailed planning was required from the outset, with the logistical constraints identified as being key to the success of the project.

The design called for a reinforced, stabilised and encapsulated block of soil underneath the building. This was successfully achieved by inserting 1097 two-metre in diameter interlocking jet grouted columns to a depth of eight metres capped with a thick concrete slab. Over 15,000 tonnes of cement was used in the grouting and associated work.

This was a high risk project in terms of design, construction and safety. It also had constraints and logistical challenges associated with working inside the building which is heritage listed.

Close collaboration and integration with both the client, Hawkins and the consultant demonstrated the benefits of working together as a team in this project with regular meetings and liaison maintained throughout the design and construction period.

The Brian Perry Civil and Keller Ground Engineering team not only developed solutions that were both innovative and cost effective, they also raised the bar in terms of construction process and safety standards. The completed project complies 100 percent with new building standards and since completion has withstood further after-shocks and a 5.7 magnitude quake in 2016. l