Analysis of Temperature Anomalies during Thermal Monitoring of Frozen Wall Formation

Abstract

The paper describes a distributed temperature sensing system that was used to monitor the artificial freezing of soils during the construction of a potash mine shaft. The technique of reconstructing the temperature field by solving the inverse problem in the entire volume of frozen soils using the measured temperatures in four thermal monitoring (TM) wells is described. Two local anomalies in temperature distributions in TM wells are described and analyzed theoretically using thermo-hydraulic modeling. The first anomaly concerns the asymmetric temperature distribution in one of the soil layers and is associated with the influence of natural groundwater flow in the horizontal direction. The second anomaly consists of a sharp decrease in water temperature in the section of the TM well located inside the freezing contour. Calculations showed that it is most likely associated with the entry of cold groundwater from the overlying layers of soils through a well filter at a depth of 160 m and the subsequent movement of the water up the well.

Analysis of the structural integrity of a frozen wall during a mine shaft excavation using temperature monitoring data

“…The spatial temperature distributions in the CT boreholes were generally correlated with each other, except for a small zone at a depth of 140 m, where a local maximum was observed in CT-2, and a local minimum was observed in CT-3. This feature was associated with the groundwater seepage in the sandstone layer at this depth, which was described in detail in [20]. Fig.…”

“…The horizontal soil layers had thicknesses of 10 m or greater. Regarding the middle horizontal sections of these soil layers, it was appropriate to accept the hypothesis of the smallness of vertical heat transfers and consider the heat transfer in the horizontal plane of each of the layers within the framework of the following mathematical model [20]:…”

“…It was for these temperatures that the design thicknesses of the FW were calculated.  Sufficient freezing of the soils at a depth of 140 m, where the seepage flow of the pore water was revealed [20]. In addition to this, the analysis of the dynamic change in the FW bearing capacity presented in this paper was conducted after the construction of the skip shaft in the AGF interval of 0 to185 m. Moreover, the analysis conducted in the present study will be useful primarily for mine shafts that will be built in the future.…”

Spatio-temporal analysis and volumetric characterization of interferometric synthetic aperture radar-observed deformation signatures related to underground and in situ leach mining

“…After careful reconsideration of mining operations at McArthur River, we examine the possibility of ground freezing contributing to subsidence at the site via thermal contraction of the rock matrix. Ground freezing is done as a safety precaution to protect against harmful materials removed during the mining process; a more in-depth discussion as to how this procedure works is discussed in the literature 6 , 27 , 28 . Generally speaking, ground freezing is accomplished by pumping cooled brine into an underground system (e.g., around mining zone locations) at temperatures between −25°C (248 K) to −35°C (238 K).…”

“…Ground freezing is done as a safety precaution to protect against harmful materials removed during the mining process; a more in-depth discussion as to how this procedure works is discussed in the literature. 6,27,28 Generally speaking, ground freezing is accomplished by pumping cooled brine into an underground system (e.g., around mining zone locations) at temperatures between −25°C (248 K) to −35°C (238 K). The brine freezes the surrounding rock matrix into which it is pumped, essentially creating a protective barrier around harmful materials.…”