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Work on raising 30 000 tonne Art Gallery under way

Christchurch Art Gallery

An injection unit is pumping bursts of quick setting grout into space created beneath the basement garage floor

4 March 2014 - Months of preparatory work to lift back to a level position the 30 000 tonne Christchurch Art Gallery Te Puna o Waiwhetu is coming to fruition as the building is raised millimetre by millimetre.

Stephen Hogg, technical director for Aurecon, said that the Christchurch Art Gallery settled up to 150 millimeters lower on one side of the building following the Canterbury earthquakes.

Quick-setting grout is being pumped into spaces between the foundations and recently built columns beneath the floor to help raise and level the building. The technique was first tested on a smaller building in Christchurch with such success that we had confidence to undertake the Art Gallery project. 

Stephen and Aurecon senior structural engineer, Forrest Lanning, are overseeing the multi-million-dollar repair of the Art Gallery and have contracted re-levelling works to international experts Uretek and The Chemical Grouting Company of Japan.

“Levelling a building of this size using this technique has never been undertaken in New Zealand, but our earlier tests were extremely successful,” Stephen Hogg said.

Re-levelling the building includes creating 100 cement columns underneath the Art Gallery, each three metres in diameter, which provide the platform to enable the building to be lifted and levelled. More than 25 000 bags of cement will be used.

To form a cement column, you drill a small hole through the foundation and then basically stick a pipe with an angled nozzle at the end to a depth of seven metres below the foundation. You then start pumping high-pressure grout out while spinning the pipe and slowly pulling it back out.

The grout travels out with such tremendous force it blasts the soil out of the way and you’re left with a nice three-metre-diameter cement column beneath the building.

The key is stopping a metre short of the foundation. This forms a void between it and the new cement columns.

This is repeated for each of the 100 columns that help ensure the Art Gallery’s basement footprint is covered.

The rest is a practical application of Isaac Newton’s theory that any action has an equal and opposite reaction. The columns provide a solid platform to start pushing off against as the building is lifted.

The metre-high void left between the new cement columns and the existing foundation is where the magic of lifting happens. Shorter pipes are inserted through the foundation to the void. Quick-setting grout is pumped through the pipes to the point where the void is overfilled. It builds enough pressure to start pushing the Gallery upward a millimetre at a time.

The grout is pumped in small bursts against the cement columns. These harden in seconds, pushing down against the columns. The next burst of grout shoots against the previously hardened grout, pushing off it and slowly raising the building.

The end result looks something like the Punakaiki Pancake Rocks, with blobs of hardened grout sitting on top of each other.

The pumping of the quick-setting grout is computerised and up to 90 locations can be synchronised at one time. The computer automatically compensates if one area gets ahead of another.

Up to 5 000m3 of grout will be used in the construction of the columns and the lift.

Christchurch Art Gallery director Jenny Harper says, like many others she speaks to about the repair work, she finds the process fascinating.

“The precision, calibration and expertise required to undertake a project such as this boggles the mind,” she says. “But the fact that the Gallery is now, quite literally, on the rise is a wonderful milestone and a welcome reminder that we are well and truly on the way to reopening in late 2015.”

Further information:

Stephen Hogg
Technical Director, Aurecon
T: 03 371 2042; M 027 240 8212
E: stephen.hogg@aurecongroup.com

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