THM Experiment for the Investigation of Freeze-Thaw Processes in Unconsolidated Rock and Geotechnical Grouts

Freezing and thawing in the subsurface is often associated with a complex technical handling of possible influences on the engineered structures (e.g. ground freezing, permafrost, geothermal heat pumps). However, detailed knowledge on freeze-thaw processes in porous media, such as unconsolidated rocks or geotechnical grouts, is still pending. Freezing in porous media does not occur as a sudden transition from pure liquid water to the ice phase, but rather within a freezing interval strongly depending on various boundary conditions such as soil type or pore water chemistry. As the content of frozen and unfrozen water has a strong impact on material properties, it is essential to have adequate information about the different factors influencing freezing processes as well as the thermo-hydraulic-mechanical (THM) effects on porous media due to phase change. Therefore, a THM laboratory experiment was designed and built to gain more detailed knowledge on freeze-thaw processes and their effects in porous media. A modified triaxial test, enabling for a confining pressure up to 1.2 MPa, is linked with an ultrasonic measurement device to determine the unfrozen water content at defined boundary conditions. The confining pressure fluid (water-glycol-mixture) can be tempered via a cooling circuit down to -25 °C. Axial and radial deformation of the specimen are measured as well as further mechanical parameters such as the freeze pressure. Furthermore, the hydraulic conductivity of the sample is determined to investigate the influence of water flow on the freezing process.