| Title | Coupled Measurements of Thermopysical and Hydraulical Properties of Unsaturated and Unconsolidated Rocks |
|---|---|
| Authors | Ingo SASS and Johannes STEGNER |
| Year | 2012 |
| Conference | Stanford Geothermal Workshop |
| Keywords | unconsolidated rocks, thermal conductivity, thermal diffusivity, hydraulic conductivity, water retention function |
| Abstract | Thermal conductivity and diffusivity as well as the hydraulic properties of unconsolidated rocks are the most important parameters required to quantify subsurface conductive and convective heat transfer. Soil mechanical and mineralogical constraints such as thermal conductivity of the individual grain fractions, the bulk dry density and the pressures remain constant. On the other hand, temperature and water content in the unsaturated zone are highly variable in time and space. The variations of the ratio between the gas phase and the water phase occupying the pore space has a varying thermal insulating effect due to the low thermal conductivity of air. In addition, the unsaturated hydraulic conductivity is a function of the water content of unconsolidated rocks. The air in the pore space reduces the effective conductive cross-sectional area, which leads to a decrease in hydraulic conductivity. Increasing drainage induces negative pore pressure (suction) and due to the hysteresis in drainage and irrigation thus the local water distribution is changed. Presented herein is the implementation of a newly developed thermal conductivity and thermal diffusivity meter for the integrated investigation of soil mechanics, hydraulic and geothermal properties of unconsolidated rocks. Patent applications are pending. Furthermore an evaporation test was developed and columnar drainage experiments with continuously conducted measurement of water content, pore pressure, and thermal conductivity at different levels of the column. To simultaneously measure the hydraulic properties as well as the unsaturated thermal conductivity they are equipped with a full-space line (heat) source. In these experiments many different unconsolidated rocks are examined in order to provide the respective parameters for a new capillary tension/ thermal conductivity function analogue to the existing capillary tension/ water content functions. |