Engineering geological mapping for urban areas of the Oltrepo Pavese plain (Northern Italy)

The objective of the study was to develop a methodology for engineering geological mapping to support urban planning and development. The study area is located in the province of Pavia and corresponds to the Southern and Central sector of the Po River Plain (Northern Italy). It has an extent of about 440 km 2 and several important urban areas are located there. Geomorphologically, fluvial terraces and piedmont fans characterise the area. The recent river deposits consist mainly of coarse-grained units (sand, pebbles, gravel). The upper part of the older alluvial deposits are strongly weathered and composed of a large amount of clay. The adopted approach was multidisciplinary, such that data regarding the geology, geomorphology, hydrographic network, urban development and history of the towns were used to develop a geological/geotechnical model of the area. In the first step the landforms (alluvial terraces, alluvial fans, etc.) were mapped from aerial photographs. In the second step, for each landform the nature of surface materials (lithostratigraphic, hydrogeological and geotechnical characteristics) was determined. The datasets included boreholes and trial pits. Collection of penetrometer results (DCPT, SPT and CPT), calibrated against soil profile logs, helped with the geotechnical characterisation of the soils. Geotechnical and lithological profiles were then constructed. Engineering geological zoning was carried out by assessing three attribute groups: lithologies, geometries, and geotechnical characteristics. The resulting engineering geological units (areas that may be regarded as homogeneous from the geomorphological and engineering geological point of view) are useful for studies concerning geohazard susceptibility and foundation conditions.