Thermo-hydraulic modeling of artificial ground freezing: Application to an underground mine in fractured sandstone

Abstract

The difficult geological conditions of underground mines in permeable and fractured rocks require the use of ground support and inflow management methods. Artificial ground freezing offers the opportunity to reduce the permeability of the ground and to consolidate it. However, the establishment of this technique can be made complicated by two phenomenas: the strong ground heterogeneity, which renders delicate an overall freezing prediction, and the potential presence of high seepage-flow velocities, which may have a negative impact on freezing progress. The present article presents a coupled use of the thermo-hydraulic model and the freeze-pipe ground model presented in Vitel et al. (2016, 2015) with an application to the Cigar Lake underground mine in Northern Saskatchewan, Canada. The first model allows the estimation of the temperature and pressure distribution in the ground during freezing while the second model simulates the heat transfer between a freeze pipe and the surrounding ground, which is useful to determine the boundary conditions of the thermo-hydraulic model. First, the article restates the governing equations of both models. Then, after the validation of the numerical results with respect to field measurements, a joint use of the models is proposed, in particular to (i) predict the ground temperature evolution, (ii) study the impacts of the geological conditions on the freezing progress and (iii) optimize the freezing system design.