Excavation Failure & Building Collapse

Cremorne NSW

A series of underpinning excavations associated with a large basement excavation on a construction site in Cremorne, resulted in a partial collapse of an adjacent building.  Although the proposed underpinning was reinforced concrete panels to support the adjacent footings, during the excavations for the underpinning, the wall of the adjacent building started to crack, and some hardwood timber props and a steel Acrow prop were put in place as an emergency support measure.

However, after the construction site was closed for the night, the movements of the adjacent building continued, leading to the partial collapse of the wall which had been supported by the emergency props.

Shirley Consulting Engineers were engaged to investigate and advise on the site conditions and cause(s) of the failure, following a request for an "independent" investigation of the building collapse by the WorkCover Authority of NSW.

The investigation involved the careful excavation / exhumation of the collapsed building debris, extensive photographs, measurements, site sketching, analysis of the adjacent building cracking patterns and determination of the probable mechanism leading to the failure.  It was found that the temporary propping had failed gradually, following the bending of the Acrow prop and sudden breakage of one of the hardwood timber props, followed by collapse of the building wall.