Water damage could have caused the collapse of an Italian building site last week, a geotechnical expert has told New Civil Engineer.
The collapse in the Balduina district of Rome happened when a piled retaining wall surrounding a 10m deep excavation at the site failed, destroying a road and causing the emergency evacuation of two nearby buildings.
No one was hurt.
Mott MacDonald geotechnics global practice leader Tony O’Brien said that it appeared that the piled wall had rotated into the excavation, causing the road to collapse behind it, taking several cars with it.
It is not yet known what caused last Wednesday’s collapse. Italian media reports say there have been several cases of fragile water pipes leaking into the ground in the Balduina district, affecting the structural stability of the buildings.
#Roma #15feb, proseguono le attività di verifica dei #vigilidelfuoco a causa della frana che ha interessato la zona della #Balduina: sul posto il nucleo #SAPR (sistemi aeromobili a pilotaggio remoto) e sistemi #Georadar di #vigilidelfuoco e @SapienzaRoma pic.twitter.com/38K476gF1w— Vigili del Fuoco (@emergenzavvf) February 15, 2018
O’Brien said that, although it was too early to tell what caused the collapse, water was the cause of many geotechnical failures. He said even very small movements in the soil could cause ageing pipework to crack, allowing water to be released. This, he said, could have added load to the back of the wall and could also have weakened the soil, affecting the stability of the works.
“From looking at photographs it’s not sensible to go into detail about what the failure mode might be, but it’s an interesting looking failure,” he said. “Often these failures can be traced back to a misunderstanding of the site history or the geology or hydrology. Were these water pipes surveyed before the excavation progressed?
“Often ground water is a very common cause of geotechnical failures,” he said.
Photographs from the Rome Fire Department appeared to show no internal propping on the site. O’Brien said it was not unusual but it depended on the ground type and the design of the retaining wall.
However, he added that minimising ground movements was the primary concern in urban areas. This could involve the construction of a stiff retaining wall system for the entire wall height. He said it was therefore unusual for the piled wall to only be part height around the excavation with a different construction formed above it.
The University of Rome and its geotechnical engineering spin-off company Nhazca have installed remote sensing instrurments to monitor for further wall movement at the site.