Plans to encase the historic Wall Street causeway in glass appear to be over after more than half of the logs were found to be rotten.
The deteriorated part of the causeway would be buried in situ today and the salvageable part rebuilt on a different location on the Wall Street site, project manager Dave McKenzie said yesterday.
"We have found 60% of the causeway is so deteriorated that it can't be preserved," he said.
The remaining 40% had been taken off site, immersed in a skip filled with water, and the developers were awaiting a visit from a wood conservator from the University of Auckland in the next few days.
"We don't know what the next step will be," Mr McKenzie said.
"We are in a holding pattern until the conservator gets here."
Historic Places Trust Otago Southland area manager Owen Graham said the council had employed experts to save the causeway and hoped the right decision would be made.
"We trust that advice is good advice and the city is still working towards the conservation of the material."
The causeway, unearthed on June 27 at the Dunedin City Council's $34 million Wall Street development, has been described as a find of national importance by the trust.
The council's economic development committee last month approved a decision to retain and display the 150-year-old causeway in glass at a cost of $310,000 rather than spending $40,000 to rebury it.
The price included the cost of driving sheet piling around the edge of the 12m causeway to protect it from flood risks.
Some initial piling work had been completed, but that would now be abandoned.
The causeway, made from manuka and kanuka, had been deteriorating for years before it was discovered, Mr McKenzie said.
The deterioration was not the fault of developers.
The eastern part of the causeway had begun to deteriorate due to it being raised out of the water which had previously helped to preserve the wood.
The western part of the causeway could be saved to be reassembled at a later date.
"We don't know what we will do with the 40% . . . if possible we will put it on display."
Work on the development, expected to be completed by early March, would have to "go to seven-days-a-week construction" to be finished on time.
The discovery of the causeway had added weeks to the project and final costs were not yet known, he said.
