Police will dig beneath the site of Christchurch's CTV building in search of clues as they investigate its fatal collapse.
The collapse of the building accounted for 115 of the 185 deaths in the February 2011 earthquake but so far nobody has been held responsible.
On Monday, eight trenches will be dug around the area where the north and south walls once stood, to enable the police inquiry team to examine the foundations.
Soil specialists and engineers will carry out the work.
The latest development is despite an announcement in June that police had completed their investigation and were about to hand it to the Crown for a decision on whether charges could be laid.
Inquiry head Detective Superintendent Peter Read said the decision on charges was now expected to be made later this year.
He was unable to be more definitive at this stage, he said.
Last year police raided the offices of structural engineer Alan Reay, whose firm was linked to the CTV collapse during the Royal Commission into the disaster.
Police subsequently broadened the investigation to include other buildings that had collapsed and killed people.
Investigators had interviewed more than 100 witnesses.