Effects of Salts Solutions on Thermal Conductivity of Clayey Soils.

Clayey soils may be used as the most-outer barrier covering the outside of high-level radioactive waste containers at a geological disposal site. In recent years, experimental disposal sites, of which most of them are located near coast, have been proposed in Japan. In such locations, sea water may seep into a disposal site and contat with the most-outer barrier. The effects of salts on thermal conductivity of soil have left much uncertain. To give a complete view of a barrier material, it is necessary to understand the effect of water content and salt solution concentration on soil thermal properties. The objective of our research was to investigate salt-dependent thermal properties of clayey soils. A swelling montmorillonitic soil, a non-swelling kaolinitic soil, a amorphous allophane　soil, and toyoura-sand were used. Solutions of NaCl and CaCl₂ were prepared with concentrations ranged between 0 and 1.0 mol/L. Soil was mixed with the predetermined concentration of salt solution for various volumetric solution contents of soil. A mixed soil sample was packed in an acrylic column, and equilibrated to the room temperature (=20^OC). A three-wire thermo-time domain reflectometry (TDR) probe (0.040 m long, 0.0075 m spacing, Nichrome heater wire encased in the central rod and type T thermocouples in the rods of both sides) was used for measurements. Thermal properties were determined with a dual-probe heat-pulse technique. The more detailed results will be discussed.