Temperature anomaly as an indicator of groundwater flow prior to the shaft sinking with the use of artificial ground freezing

The study aimed to evaluate hydrogeological conditions for shaft sinking using artificial ground freezing in complex geological formations of the Upper Silesian Coal Basin (USCB) in Poland. Temperature logging was conducted to a depth of 460 m in five boreholes positioned around the freezing cylinder and four boreholes along the radius extending beyond the freezing cylinder. An effective borehole temperature acquisition system was created using autonomous sensors. A novel approach was developed for the quantitative assessment of temperature anomalies, enhancing data processing and interpretation. Two types of temperature anomalies-negative and positive-have been defined related to groundwater convection. The locations of temperature anomalies strongly correlate with the hydrogeological and lithological data obtained at the stage of preliminary geological recognition. Negative anomalies indicated increased temperature in aquifers, including fractured and tectonically disturbed zones. Positive anomalies indicated decreased temperature in zones of poorly permeable rocks. The study revealed that temperature anomalies not influenced by the geothermal gradient are almost half the size of those influenced by the geothermal gradient. The findings provide more effective insights into the applications of borehole temperature measurements to better monitor the freezing process. In the stage of shaft sinking, the research contributed to modifying the freezing technology and strengthening the shaft lining.