The failure of an earth retaining wall: investigation and assessment of the causes

After seven years from the end of construction, a reinforced concrete cantilever wall sustaining a 9 m high embankment along a State Road in Italy, showed a sudden and unexpected outwards displacement at its top. This event caused the immediate closure of the traffic over the road and promoted an investigation by the Contractor to design and implement suitable remedial measures. Early interpretations suggested that a rigid rotation of the entire wall may have occurred due to a bearing capacity failure, so that the underpinning of the wall base through bored piles was planned. However, during the repairing works, the wall stem rotated and collapsed by full overturning. In Italy every collapse involving public works has to be prosecuted, irrespectively of the severity of the consequences and a judicial investigation was then open implying new analyses and studies even by the Contractor. In the paper, the results of these latter studies are presented and the factors playing a role in the collapse are analyzed.