INFLUENCE OF UNDERGROUND STRUCTURES AND INFRASTRUCTURES ON THE GROUNDWATER LEVEL IN THE URBAN AREA OF MILAN, ITALY

Underground structures and infrastructures (i.e. metro tunnels and stations, deep foundations, etc.) locally affect the groundwater level of the aquifers in urban area, and they can bring about hydrogeological hazards especially in areas also interested by a regional raising trend of the water table. In this paper, the case of Milan (Italy) is discussed by means of the following steps: (1) monitoring data analysis for reconstructing the regional increasing trend of the water table; (2) numerical modelling of the groundwater flw system in steady state; (3) numerical modelling of the interference of underground structures and infrastructures with the aquifer system. More in detail, the study started from a numerical model of the aquifer system of Milan, calibrated in steady state with reference to the maximum water table observed in May 2014. Afterwards, a pilot sub-model of about 9 km2 was refied to simulate the major intersections between the metro lines and the stations. Modelling results pointed out a local increasing of the groundwater levels of about 10–15 cm over wide areas located nearby the tunnels intersections. Unfortunately, these areas coincide with those areas interested by the highest increase in water table due to the regional trend. Therefore, even if the local changes are quite low, they can negatively affect underground structures and buildings because of the superimposition of effects