Design effects on the accuracy of soil temperature measurements in thermometric wells

Abstract

Introduction. Temperature sensor systems installed in wells at various depths are widely used to monitor temperature conditions in permafrost soils. In this case, sensors are typically located inside special tubes protecting the equipment from mechanical and chemical impacts. However, design features of these tubes, such as material and diameter, can affect the efficiency of heat transfer from soil to the sensor and thus the accuracy of measurements. Moreover, the issue of thermal insulation for the above-ground part of the protective tube is relevant to eliminate the influence of air temperature on the readings of temperature sensors.

Aim. To determine the reliability of soil temperature values by depth depending on the thermometric well design; to develop the most optimal design of a thermometric well.

Materials and methods. The method involves analyzing archival survey and design documentation, as well as regulatory and other technical sources, conducting soil container experiments, and developing recommendations for taking into account the design parameters of thermometric wells when measuring the temperature of permafrost soils.

Results. The optimal design of a thermometric well is determined in experimental studies. Recommendations for amendments to SP 25.13330.2020 and State Standard 25358-2020 are provided.

Conclusions. For routine monitoring, protective PVC or steel tubes with a diameter of 57 mm should be used. The studies of the exact soil temperature in the seasonal thaw layer should consider the error caused by steel; otherwise, a PVC tube should be used. The head of the tube must be reliably thermally insulated.