The Role of Cementation and Electrolyte Concentration in Marine Clay Behavior

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1. The samples of Ariake clay sediment contain smectite, vermiculite, kaolinite, illite, and chrolite as clay minerals, and the smectite content varies from 50% at the surface zone to 20% at the depth of 17m. The chlorine concentration of the clay sediment increased from 0.07N at the surface zone to 0.3N at the depth of 4m and then decreased to 0.01N at further depth. The variation of the ratio of undrained shear strength against overburden pressure was explained in terms of the clay content and salt concentration, and another factor of pH was added to explain the variation of the liquid and plastic limits.2. A negative correlation was observed between the mean particlediameter of flocks in the suspensions and the zeta potential. The sediment volume of the clay suspensions of pH7 was found to be positively correlated with mean particle-diameter of flocks. The void ratio of the sediment exhibited a rapid decrease with increasing depth at the surface zone and a subsequent slow decrease at greater depth.3. Addition of the iron oxides to the illite increased the yield stress over a pH range of 3 to 10. With increasing pH the yield stress decreased for for the complexes with iron oxides of 2 and 5% while the complexes with iron oxides of 7, 10, and 20% exhibited the maximum yield stresses at the pH values of 6 to 8. The yield stress for the complexes was correlated with their zeta potential, and the higher yield stress was explained to be due to smaller interparticle repulsion.