Available methods for the identification of the foundation system and depth in case of existing bridges

The new Italian “Guidelines for classifying and managing the risk, assessing the safety and monitoring existing bridges” (LLG) are based on a multi-level and multi-risk approach. The Level 0 of this approach is focused on collecting the basic information about both the bridge under consideration and the environment in which it is located (for the assessment of seismic, hydraulic and landslide hazards). These can be retrieved in the project documentation, via available seismic/hydraulic/landslide hazard maps, accelerometric and hydraulic monitoring stations and interferometric data. The Level 1, instead, consists of carrying out visual inspections and compiling some inspection forms for each risk (structure-foundation, seismic, hydraulic and landslide). Then, in the Level 2 all the collected data are organized and used for defining the so-called Class of Attention (5 classes: low, low-medium, medium, medium-high, high) for each risk and the overall Class of Attention. Based on the experiences gained in the last three years by the geotechnical staff of the University of Pisa (member of the FABRE Consortium) one of the main issues encountered in the Levels 0 and 1 (and therefore in the Level 2) was the difficulty to properly identifying the type, geometry, layout, material, and depth of the foundation system of existing bridges. This contribution is focused on describing Non-Destructive Tests, such as Low-Strain Surface tests, Low-Strain Down-hole tests, Parallel Seismic testing (PS) and Electrical Resistivity Tomography (ERT) with the aim of showing main capabilities, limitations, and field of application. These techniques can be useful to improve the classification of existing bridges according to the new Italian Guidelines.