The “Strange” Case of the Scorciavacche Failure

Just after the completion of the upgrading works of the SS 121 national road connecting Palermo to Agrigento, in Sicily, the brand-new embankment linked to the northern abutment of the Scorciavacche viaduct suffered of two instabilities along the downhill side slope, causing the loss of two separate road segments of around 250 metres of total length. Early bird interpretation of the collapses ascribes the failures to a bearing capacity problem, consequence of the inadequacy of the embankment foundation. Surprisingly for the many actors on the scene, the subsequent forensic investigations have shown that the causes of the failure were different and not at all easily readable from the non-exhaustive observations of the initial scrutiny. Thorough geological and geotechnical investigations together with the monitoring of the site over a wide area made instead possible to discover clear signs of a quiescent instability which was bounded by a pre-existing failure surface that undoubtedly played a role in fixing the geometrical features of the collapses. The different picture of the scene that emerged after a careful geomorphological survey, a sound geotechnical investigation and a sufficiently long monitoring, convinced the technical experts of the defence that a wider scale model was needed to interpret this failure case that could not so simply be reconducted to a classical bearing capacity problem.