DIN Standards Committee Building and Civil Engineering
Determining the thermal conductivity of soils using the needle probe method
Abstract
Determining the thermal conductivity of soils is of key importance for many geotechnical applications, particularly in the design of buried high voltage direct current (HVDC) cable routes. As power cables emit heat, it is crucial that the ground dissipates this heat efficiently to avoid overheating and damage to the cables. The approach proposed in the draft standard is specifically designed for the specific requirements of underground cables. However, the results can also be applied in other areas, such as geothermal energy. The better the thermal conductivity of a soil, the more effectively the heat generated can be dissipated, which increases the performance of underground cables and at the same time ensures their operational safety. Despite its importance, there is currently no standardized method worldwide for determining the thermal conductivity of soils. International standards, such as ASTM D 5334, offer methods for measuring thermal conductivity, but only regulate the construction of the needle probe and the determination of thermal conductivity on the basis of these measurements. Important boundary conditions for the measurement methodology, such as soil-specific sampling and preparation, are not described in ASTM D 5334. This often leads to unreliable and difficult to reproduce results. The aim is therefore to develop a test methodology for all soil types that provides unbiased, plausible and reproducible results, taking into account factors such as water content, degree of compaction and dry bulk density, which strongly influence thermal conductivity. The needle probe method is a proven method for determining the thermal conductivity of partially saturated soil samples and is both more economical and practicable, especially in comparison to the plate measuring method or other large-scale tests. It allows measurement with a low measurement uncertainty and can be used in many soil laboratories with standardized equipment. Nevertheless, there is still a need to standardize the exact test boundary conditions in order to ensure reliable and comparable results. A clear definition of the test procedure using the needle probe method is therefore essential to ensure a consistent and practical determination of the thermal conductivity of soils.
Begin
2024-10-17
Planned document number
DIN 18231
Project number
00519864
