Teflon-pads plan to shift heritage pub

Teflon pads could be used to move Auckland's historic Birdcage Tavern away from the Victoria Park motorway tunnel site on long "runway" beams beside Franklin Rd.

Structural engineer Adam Thornton, who has master-minded the transfer of several large and notable buildings, including Wellington's Museum Hotel, is confident the Birdcage can be moved 30m up Franklin Rd - as proposed by the Transport Agency - without undue risk to its 123-year-old brickwork.

Neither does he believe there would be any greater risk in moving it back to its existing site overlooking Victoria Park, once the $430 million tunnel project is finished.

"It should be no greater [risk] and should be able to be managed fine," Mr Thornton said. "I'm not saying it should be done - I'm just commenting on what is possible."

Disused railway tracks and a fleet of 96 bogeys were used in 1993 to haul the 3500-tonne Wellington hotel on wheels 120m, to make way for the national museum, Te Papa.

The move was completed in two days, after four months of preparation.

Mr Thornton said that technique was unlikely to be practical for a brittle old brick building such as the two-storey Birdcage, "which needs to be held very level at all times."

But he believed methods used by his consultancy Dunning Thornton to move Waihi's historic Cornish Pumphouse 300m from the edge of a collapsed mine shaft could work.

The 1840-tonne, three-storey pumphouse, built in 1904 and a far heavier building than the Birdcage, took three months to be shunted to its new position overlooking Waihi's main street in a $4.2 million operation.

Much of that was spent on earthworks clearing the way for the move.

Mr Thornton believed the $8 million to $10 million the Transport Agency has allocated to meet resource consent conditions would be more than enough for the Birdcage move.

But he said he had not worked on the Birdcage, and did not know details of ground conditions or what seismic strengthening would be needed to give the hotel a new lease of life.

The Waihi operation included laying pairs of concrete beams 18m long with stainless-steel surfaces to form parallel tracks, over which the pumphouse was slid on teflon pads.

As it cleared one pair of beams, these were rejoined to the front of the tracks, to be traversed five more times.

Although the pumphouse was made of concrete, Mr Thornton said his firm had also used a combination of teflon and stainless-steel surfaces to move a two-storey brick heritage building from the path of Wellington's inner-city road bypass.

"It provides a good sliding surface because of the low co-efficient of friction between teflon and stainless steel."

Mr Thornton said he had no data to comment on the engineering feasibility of moving the Birdcage back above the motorway tunnel's southern portal, which designer Richard Reid believes would offer the best urban design, but which the agency insists would require a unacceptably steep descent for traffic.

Auckland civil engineer Peter Riley says the easier and more sensible alternative to digging a deeper tunnel to maintain adequate vehicle space would be to taper a roof extension with suitably strengthened concrete.