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The new Dunedin Hospital build seems set to become more complex and more costly, after drilling on the site found soils that will make the project more difficult.
Hold-ups in the geotechnical work and results have also caused a further delay of several weeks to the already overdue master site plan, which was expected at the end of last month.
Southern Partnership Group chairman Pete Hodgson said it was not clear yet what the effect would be on the planned starting date of 2020, despite logic suggesting the problems would delay the build.
Mr Hodgson said the delay of several weeks until the master site plan was finished was because there was not "sufficient geotechnical evidence to be sure where it might be best to place each of the main buildings''.
"In particular there is apparently a change between alluvial material underground and sedimentary material underground; in other words mud.''
That meant there were two types of material on a potential building site.
While it was possible to build on such ground with "decent foundations'', there was complexity in the transition from one material to the other.
"We are not yet sure where that transition occurs, and how clearly demarcated it is.''
While it would still be possible, to build, it would be more complex and costly.
``It is sensible to have better information than we have now before announcing where we think the main inpatient, or ward block, will go, and where we think the main outpatient building will go.''
Mr Hodgson said the University of Otago dental school building had faced a similar issue.
The Otago Daily Times reported last year inconsistent ground conditions had delayed work on the $130million dental school project.
The conditions meant different piles were needed, which took longer to install.
At one point last year the cost of the problem to the university was $1million.
Mr Hodgson said it was not straightforward as to whether or not the problem would delay the hospital build.
"Logically, that would delay the start date,'' he said.
However, it was not certain it would, "largely because decisions still need to be taken on how to best phase the buildings''.
Asked if he was still expecting a 2020 start date, he said that was more dependent on decisions yet to be taken about the phasing of different buildings, and the workforce needed, than it was by the geotechnical delay.
Mr Hodgson said he hoped to have a better understanding of phasing before Christmas.