Christchurch earthquake: Wrecker's tip for leaning tower

The Hotel Grand Chancellor in central Christchurch city. Photo / Sarah Ivey

A demolition expert believes Christchurch's tallest hotel, the Grand Chancellor, will probably have to be knocked down by dropping a wrecking ball through the roof above its 26 accommodation floors.

"It will have to be done straight away - it's not the sort where you can actually deconstruct it, because it is leaning," said Demolition and Asbestos Association president Diana Stil.

Ms Stil is in Christchurch to join other industry experts in advising civil defence authorities on how to clear central Christchurch of earthquake debris.

"When I saw it last night it was very unstable. You can't load it - it's already leaning, collapsing on one side - so the scenario of a ball and crane is probably the safest as that means there is no human exposure.

"We believe it can't be saved, but that's up to construction engineers."

Ms Stil, a director of Auckland-based Nikau Contractors, said something like a 250-tonne high-reach crane was likely to be needed to tower above the 85m hotel in Cashel St to drop a wrecking ball through the roof "to get into the centre of the loading and collapse it inwards".

"Because it is shifting it is unsafe to put humans on top, to manually deconstruct it," she said. "It's got to be mechanically done, and putting weight on there to do it is unsafe as well. The idea is to do it at arm's length."

A vertical-action wrecking ball would minimise danger to surrounding buildings, although Ms Stil could not guarantee that there would be no more damage to some which had been left in a parlous state by the magnitude 6.3 earthquake.

Neither could she rule out prospects for stabilising and repairing the building, although she said it seemed unlikely given the suspected extent of damage to its foundation piles.

Alec Burrell, of Auckland's Burrell Demolition, said it was unlikely that controlled explosives could be used to bring down the building because that would involve long preparations requiring people to enter the building to lay them.

"But at this stage no decision can be made until things have stopped moving," he said. "Maybe it will be possible to take off the damaged side floor-by-floor and then rebuild it on new piles. I have no idea, but it would be a lot cheaper than mowing the whole thing down and starting again.

"Until the engineers are allowed a proper look at it nothing can be done - it might look 10 times worse than it is."

Mr Burrell said local contractors and structural engineers would be well up to the challenge of dealing with the building - a task which would be far more straightforward than the Newmarket motorway viaduct project.

"What concerns us is the Aussies or Yanks may say nobody around here can do it and they'll bring in a bunch of people and God help us."

A spokeswoman for Civil Defence Emergency Management said last night that structural engineers were still assessing the hotel.

Frank Delli Cicchi, group general manager of the Singapore-based owners, Grand Hotels International, said from Wellington that he had not received any progress reports on the insured building but he was pleased that all guests and staff managed to get clear of it after the earthquake.

He was unsure how old the building was when his company bought it in 1995, after it was converted from an office block to a hotel with 176 rooms and carpark, although Quotable Value records show that a new title to the site it occupies was issued in 1991.

Associate Professor Charles Clifton, a seismic engineer who was attending a seminar with other Auckland University experts in a hotel next to the Grand Chancellor when the earthquake struck, was surprised at the extent of damage to it.

But he said the earthquake hit central Christchurch with more than twice the intensity of the larger magnitude 7.1 but deeper-seated quake of September 4.

He said Tuesday's quake was of a force statistically unlikely to occur more than once in 1000 years and produced ground acceleration 1.5 to 1.8 times greater than modern buildings were designed to withstand.

That compared with about 65 per cent of the design loading exerted by the September quake, from which the damage was mainly confined to pre-1970s buildings.