Partial reactivation of a DGSD of ignimbrite and tuff in an alpine glacial valley in Northern Italy

This paper describes the surveys, site investigations, field measurements and laboratory tests carried out to analyze the stability of a slope in the Isarco alpine glacial valley, in Northern Italy, where rocks and debris of ignimbrite and tuff outcrop. This valley is crossed by the major transport infrastructures connecting Italy to the central Europe: SS12 State Road,A22 (E45) Motorway, Verona-Brennero railway, high-speed railway network TNT-T5. Recently, large deformations of the pads of a viaduct were identified and were supposed to be caused by the downslope movement of the piers. In effect, subsequent investigations and measurements revealed the existence of sliding surfaces with movements smaller than 1 cm per year. Surveys identified that movements occur at the toe of a DGSD and back-analyses revealed that the residual shear strength estimated with shearbox tests is mobilized on the sliding surfaces.