ABSTRACT
This paper deals with the development of the microstructure of pelagic clay during the consolidation. Studied materials are the core samples about 30 cm long, composed of homogeneous pelagic clay, collected from the surface layer of bottom sediments in the Ryukyu (Nansei-shoto) Trench, south of Okinawa, Japan. Architecture of constituent clay particles, together with bulk physical properties and magnetic susceptibility anomalies, are analyzed through the whole length of core samples. Void ratio, one of the representative physical properties of the samples, decreases downwards through approximately 6 to 2. Shear strength of the sample, another important property, increases exponentially through several kPa at several cm horizons to ca. 80 kPa downward. Anisotropy of magnetic susceptibility (AMS) is rather constant throughout the column, suggesting no significant particle re-orientation of magnetic minerals by consolidation. The microstructures of the samples change by burial depths are represented mainly by different architecture of clay particles linking. Clay particles are generally in flaky shape, and these flakes are linked each other by edge-to-edge and edge-to-face contacts, so-called a card-house structure, in the upper layer. This changes rapidly to face-to-face linkage, so-called bookhouse structure, at the depth of void ratio of 3.0 and shear strength of 50 kPa. The increase of the shear strength due to consolidation is resulted from this change of the clay particle architecture.
