Cathedral rebuild would mean digging deep

Deep foundations will be needed if the Christchurch Catholic Cathedral is rebuilt on its present site, church officials say.

The fate of the Catholic Diocese of Christchurch’s Cathedral of the Blessed Sacrament is becoming clearer, as new information is released on the state of the current building and land.

The Cathedral Management Board has been working to provide recommendations to the Bishop about the future of the cathedral and the Barbadoes St land on which it sits.

Board chairman Lance Ryan said yesterday there were many complex issues affecting the decision making, but they had discovered new information on the state of the current Cathedral.

‘‘On the surface it may appear that we are becalmed, but there has been a tremendous amount of investigation and study being undertaken behind the scenes.’’

Ryan said that if the cathedral was rebuilt on the existing location, specific deep foundations would be needed to support the four internal dome columns and the heavy bell tower.

‘‘The remainder of the structure could use the existing shallow foundations, which would need to be strengthened to tolerate up to 90 millimetres of differential settlement in a major earthquake,’’ he said.

If land which previously housed the school of music was used, piles 25 metres deep would be needed, he said.

The Music Centre, the old convent, was extensively damaged in the February 2011 earthquake and subsequently demolished.

Ryan had also discovered that the building capacity of the damaged cathedral has been found to be between 20 to 30 per cent of the New Building Standard. This meant the building had over 10 times the risk of collapse compared with a new building during a period of normal seismic activity.

Although the diocese now had more information on the state of the land, Ryan said there were still more issues which needed to be considered before a decision could be made, including the future population of the central city.

They would also have to work with the New Zealand Historic Places Trust, Canterbury Earthquake Recovery Authority and the Christchurch City Council on the decision.

While it ‘‘took time’’, the board was ‘‘heading in the right direction’’, Ryan said.