Coupled thermal-hydraulic modeling of artificial ground freezing with uncertainties in pipe inclination and thermal conductivity

Artificial ground freezing (AGF) has been widely used as a temporary soil stabilization and waterproofing technique in geotechnical practices (e.g., tunnel construction). Many sources of uncertainty exist during AGF. Firstly, groundwater seepage flow can adversely affect the freezing efficacy. Secondly, freeze pipe inclination inevitably occurs during installation, which is likely to yield an unfrozen path and elevate construction risk. Thirdly, as a key soil parameter, the spatial variability in thermal conductivity can also affect the freezing process. In this work, a unit cell model of freeze pipes is established by a coupled thermo-hydraulic finite element method to examine the effects of these sources of uncertainty. The pipe inclination is considered in the unit cell model by prescribing various values of freeze pipe spacing. The thermal conductivity of soil solid is simulated as a three-dimensional lognormal random field to account for the spatial variability of soil. Results are tabulated to evaluate the additional freezing time required in the AGF system due to the existence of these uncertainties. The findings are capable of determining a reasonable range of freeze pipe spacings and the corresponding critical seepage velocity, and can offer practitioners a rule of thumb for estimating freeze pipe spacing.