MATERIAL PROPERTY CHANGES IN GRANITIC ROCK DURING LONG-TERM IMMERSIONIN HOT-WATER

To study the effects of temperature and time on hydro-mechanical prope rties of crystalline rocks, a laboratory weathering test was carried o ut, in which twenty-five cylindrical specimens of biotite granite were immersed in 90 degrees C water for 2000 days. During the test, variou s measurements were made, in parallel, to investigate the long term ch anges in the specimens' physical properties such as permeability, poro sity, longitudinal wave velocity and so on. Growth of microcracks and synthesis of clay minerals were also investigated to supply fundamenta l data for the analysis. The experimental results indicate that a disc ontinuous increase in permeability takes place around 1030 days of imm ersion, although only a slight increase occurs up to 670 days. This oc curs because microcracks become dense because of chemical and physical weathering, and thus become fully interconnected to form large-scale flow paths. Halloysite and smectite were synthesized as weathering pro ducts of plagioclase in the laboratory weathering tests. A stably prod uced clay mineral changes from halloysite to smectite at around 1030 d ays. This can be explained in terms of the selection of stably produce d clay minerals dependent on the chemical condition of the solution. I t can be said that chemical weathering, i.e., hydration forming clay m inerals, is a key factor when considering the safety and integrity of structures constructed in underground rock masses and subjected to cir culation of subsurface waters for a long period of time.