A major ground collapse at Newburn near Newcastle last week could have been caused by the earlier collapse of a culvert which runs through the site in May, according to Newcastle City Council.
The washout and collapse of ground at Spencer Court by floodwater on 25 September exposed between 3m and 4m of the piled foundations of an apartment building.
Newcastle City Council engineers said they expected that it would have to be demolished. Other properties on the estate are also under threat.
More than 80 household were evacuated following the initial ground subsidence in Spencer Court that started early in the morning as flooding intensified.
Since the initial incident the ground collapse has progressed along the line of the culvert towards the area where the culvert first collapsed.
Newcastle City Council said that the ground collapse last week followed a period of prolonged rainfall.
“The culvert collapsed in May and we became aware of the problem when a hole opened up in the road at the junction of Millfield Lane and Spencer Court at that time.
Since then the area has suffered from surface flooding during heavy rainfall,” he explained.
“The floodwater has affected the Spencer Court area twice since the culvert collapsed but it was the heavy rain earlier this week that led to the erosion around the foundations of one of the blocks of flats.”
The culvert, which carries the River Dene 12m beneath Spencer Court, is Victorian.
Northumberland Estates, which owns the land crossed by the culvert, declined to comment on the maintenance of the structure.
The city council’s spokesman said the culvert used to discharge into a natural ravine south of Spencer Court before entering another culvert.
Northumberland Estates initially denied responsibility for the problem but has since issued a statement apologising to residents for the problem.
The council spokesman confirmed that repair work had started but that efforts to construct a shaft to access the failed culvert had been delayed.
Northumberland Estates said that it would take three to four months to repair the culvert.
It gave no indication of what action will be taken to reinstate land at Spencer Court.
The five blocks of flats were built by Dunelm Homes in 2006 and had been unaffected by flooding until the May culvert collapse.
Dunelm Homes has denied responsibility for the flooding or ground collapse and issued a statement to say that the cause of the damage was a culvert blockage outside its site boundary.
As NCE went to press, the block of flats was still standing but Newcastle City Council engineers said they expected that the block would have to be demolished.
Speaking before the collapse had progressed further into Spencer Court, Arup director Tim Chapman said: “The building looks in very good condition considering, but the stability of the building is dependent on the pile design.
“At the moment, it appears as if only 3m to 4m of ground has been washed out and the piles could extend to 25m below ground so it could be possible to repack the area around the piles and save the building.
“However, if only the top 5m of the piles is reinforced, then effectively the piles may only be acting as concrete columns. “If this is the case then the building is only meta-stable and any changes in the site conditions may result in catastrophic collapse,” he said.
“Thank goodness the buildings were not constructed on shallow foundations and the support of the piles allowed for the safe evacuation of residents, otherwise this might be a very different story.”