Artificial Ground Freezing for underground excavation: a coupled modelling approach supporting tunnelling design
Artificial Ground Freezing for underground excavation: a coupled modelling approach supporting tunnelling design
This study develops a numerical thermo-hydraulic model to simulate the Artificial Ground Freezing (AGF) intervention as a ground improvement. Frozen soil is modelled based on the partially saturated framework, considering a three-phase material composed of solid grains with liquid water and ice filling the voids. A physically based criterion is proposed to estimate the freezing temperature at which the soil attains the impermeable conditions and thus is completely frozen. According to this criterion, coarse-grained soils freeze around a temperature of -1°C, and fined-grained soils freeze progressively for lower temperatures, down to -9°C. The modelling approach is applied to the AGF case study of the Isarco River Underpass in the Brenner Base Tunnels project. The incoherent and heterogeneous coarse-grained soils under a water seepage regime that characterise the site, within the few-meters thin covering separating the tunnel from the riverbed, make using the AGF necessary to furnish the proper safety conditions for the excavation works. The accessible geotechnical investigation surveys and the monitored soil temperature data aimed to validate the proposed numerical model. The model predictions regarding temperatures reveal a strong dependence of the freezing process on the soil's hydraulic and thermal properties and the seepage flow regime. An optimised freezing temperature aims to improve the process of artificial freezing by reducing the time of freezing activation and designing an efficient configuration of probes, maintaining equal levels of safety against the waterproofing of the excavation area.
G. Guida; Francesca Casini; A. Restaini; A. Celot
18th European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE2024)
D - Current and new construction methods
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