Author(s): Paola Gattinoni; Loris Colombo; Fabio Marelli; Laura Scesi; Luca Alberti; Angelo Ortelli

Linked Author(s): Paola Gattinoni

Keywords: Groundwater table; Italy; Numerical modelling; Statistical analysis; Tunnel design

Abstract: When dealing with the design of underground works (i.e., foundation, tunnel, etc.) in urban areas, detailed and reliable information about the groundwater level and its fluctuation is fundamental. Common practice is to presume a groundwater level with a specified return period, empirically based on the peaks of groundwater hydrographs in the time series. Nevertheless, this kind of approach involves some limitations, arising from the relatively short time period of available data, as well as its impossibility to take into account for economic, social and environmental changes, which can significantly affect the water table. This paper deals with the identification of the designed groundwater level in urban areas interested by a water table rising trend started 45 years ago. In particular, this study pertains the urban area of Milan (in northern Italy), where previous studies analyzed the future water table trend through a groundwater flow numerical modelling approach, pointing out the related potential hazards and the possible mitigation solutions, as well as the hydrogeological hazard for the existing underground infrastructures. Starting from the reconstruction of the phenomenon previously obtained, in the present paper the 3D numerical model of the groundwater flow was coupled with statistical analyses of time series in order to overcome the above cited limitations. At this aim, the study develops starting from the simulation of several future scenarios of the groundwater flow, related to different climate and socio-economic conditions. More in detail, a combination of an intermediate climate change scenario with average recharge conditions and average withdrawal decrease was considered for the 2050. Moreover, fluctuations of the water table were considered based on the data observed in the last 35 years. Therefore, a probability distribution of the levels of the unconfined groundwater was identified and the potential hazards for the existing underground infrastructures were evaluated. Moreover, the design groundwater level was pointed out according to the Italian law (NTC 2018), in long term condition, corresponding to the expected lifetime of the underground infrastructures (equal to 150 years).

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221606

Year: 2022