The “unexpectedly intact cellar areas” with some 1,200 metres of shelf space were found on Friday and will be salvaged early this week, the city said.
So far workers have managed to recover some 17 kilometres of documents out of the archive's total 30 kilometres, director Bettina Schmidt-Czaia said last week.
The archive, which held precious documents dating back up to 1,000 years, collapsed on March 3, killing two men in a neighbouring building. Over the weekend auditors working for the state of North Rhine-Westphalia estimated that the costs of the accident could top €1 billion.
Experts believe the collapse was caused by problems at the underground construction site near the archive. Media reports revealed that construction managers and city officials saw measurements that clearly showed the archive was sinking weeks before the building collapsed into the nearby underground metro construction site.
The city has since opened an investigation into what caused the accident and has raided the offices of construction companies involved in the subway line's construction.