Study on the Reflection Coefficient of Clay from the View Points of the Microscopic Structure and the Mineralogy

Many studies have shown that abnormally high pore pressure can be generated by the act of clay as semipermeable membrane. The reason is that surface electricity of smectite composing of clay generates the electric double layer in clay pores that ristricts the migration of ions. The act of clay as semipermeable membrane has not been understood quantitatively from the view points of the microscopic structure and the mineral compositions of clay. The authors have developed a laboratory apparatus and a numerical simulator to obtain the fundamental data for the quantitative understanding of the phenomena. In this study, the samples of a tarbidite and a clay of Niigata sedimentary basin were collected. The analysis of the microscopic structure and the mineralogy and the laboratory experiments to measure the reflection coefficient were done. The large part of pore radius of clay is less than 1.0μm while the pore radius of approximately 35% of the pore volume of tarbidite is more than 1.0μm. The XRD chart of the tarbidite does not show the peek of smectite while that of the clay shows it. Based on the data that the authors have obtained so far, it is suggested that there is a relationship between the reflection coefficient and the methylene blue adsorption of clay.