An archival geomatics approach in the study of a landslide

Geomatic approaches were used to investigate a landslide in the Emilian Apennines in northern Italy which occurred during excavation works for high-speed railway tunnels between 2002 and 2007. The landslide damaged three buildings located on the upper part of a hillside. At the site of interest, the high-speed railway system included three contiguous tunnels—the main tunnel and two connecting tunnels, “odd” and “even”—all crossing the “Chaotic Complex” formation. The archival multi-temporal digital photogrammetry technique was employed for photogrammetric surveys performed in 1998, 2004 and 2007, at a mean scale of about 1:8000. For all the surveys, stereo pairs of the area were available, and the black and white photo-frames were scanned using a Wehrli Raster Master RM2 photogrammetric scanner (12-μm resolution). Digital images were obtained, with a ground resolution in the range of 9–10 cm. The reference coordinates of the Ground Control Points (GCPs), as required for the external orientation of the images, were measured in 2009 in a stable area using GPS methodology. Orientation of the images was carried out with SOCET SET software, obtaining orientation residuals in the order of a few centimetres. An approach based on the multi-temporal sets of photographs was used, comparing the coordinates and amplitudes of the motion vectors. In doing so, 3D vectorial representations were obtained, providing displacements of about 14 cm in the initial period (1998–2004) and of about 25 cm in the latter period (2004–2007). From a chronological point of view, this data corresponded with both the beginning of the damage and the progression of the excavation of the tunnels, thus confirming the vulnerability of the Chaotic Complex to stress changes during the works.