Exciting things are happening behind the Canterbury Museum façade in central Christchurch. Work is well underway on a world class new Museum and contractors have started the big dig to create the new storage basement.
The new basement under most of the Museum site and the Robert McDougall Gallery requires exceptional engineering to create a safe, waterproof and earthquake resilient underground storage space for the precious Museum collection.
And, as the above video explains, with big engineering comes big numbers. Workers will remove 25,000 cubic metres of soil from the site, which would fill 10 Olympic swimming pools. Then they will pour 9,500 cubic metres of concrete to build the basement floor and walls.
They’ve already completed the 12-metre-deep underground diaphragm wall, made of reinforced concrete, that forms a continuous waterproof barrier around the basement space. Diggers are now excavating inside the wall down to a depth of 6 metres.
The basement will have three layers of waterproofing to maintain a completely dry environment. The waterproofing technology is important as, at 6 metres deep, the basement will be 2 to 3 metres below the water table.
The 12-metre-deep underground concrete wall provides the first layer of waterproofing. If water penetrates the wall, it will be drained away from a 60-centimetre gap between this outer wall and the main inner basement space. The inner basement space will also be lined with a heavy-duty waterproof membrane to keep out moisture and water vapour.
New Zealand doesn't have standards for waterproofing basements, so the Museum space has been designed to the highest grade of the British Standard. The British Museum used this standard in 2014 for a four-storey collection storage basement that extends 30 metres into saturated ground beneath their London site.
With base isolation underneath, the new Museum building and the Robert McDougall Gallery will be able to withstand 2 to 3 times more shaking than expected from an Alpine Fault earthquake. The new building, Gallery and basement will rest on a base isolation system consisting of sliding metal bearings that absorb any shaking.
The new Canterbury Museum has been years in the planning and contractors are making good progress on the build. The Robert McDougall Gallery has been strengthened above ground, the tired twentieth-century Museum buildings demolished and the outer basement wall built. The underground strengthening of the Gallery is due to be completed by the end of the year. This will allow the building to be temporarily supported while the new basement is built underneath.
Once the basement is complete, Cantabrians will start to see the new Museum building emerge from the ground behind the heritage buildings on Rolleston Avenue. The Museum has the committed funds in hand to complete the storage basement and the new building so that they are weather-tight and insurable. If we have to pause construction to raise more money, it would be in 2028 when this stage of the project is completed.
A world-class new Museum, with restored heritage buildings, a dramatic new atrium and much more exhibition space, will rise on the site. Join us on this exciting journey to a new and amazing Museum.
