A study on method for in-situ measurement of unsaturated zones around a drift. Simplification of calibration test and development of measurement probe

It is generally considered unsaturated zones can be generated in the vicinity of a drift after excavation. Tono Geoscience Center has been conducting researches on applying time domain reflectometry (TDR) to in-situ measurement of the extent and water content profile of unsaturated zones. An improved insertion method of waveguides was applied to the calibration test of the volumetric water content θ and the dielectric constant ε relationship of four kinds of rocks, and was proved valid. Calibration labor can be reduced using the θ - ε relationship based on the three-phase mixing model estimated by a few measured data. To allow easy installation of waveguides, a method was developed that uses an air packer to press waveguides against a borehole wall. Configuration of the packer-type probe was designed to measure the average dielectric constant of the object and the buffering material. The in-situ dielectric measurement at Tono mine using the packer-type probe resulted in reproductive data at the same depth. (author)