Research into Structure and Long-term Settlement of Osaka Bay Clay

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Most, natural, sedimentary clay becomes stiffer and stronger as it ages. Similarly, a clay mixed with cement hardens with time due to the development of fabric bonding caused by chemical (i.e., pozzolan) reaction. Such fabric bonding may also occur to some degree in natural ground with a high CO_3 content.In this research, these naturally and artificially cemented clays are regarded as "structured" to the comparable behavior of a reconstituted sample, bearing in mind that the mechanical behavior of such clays is noticeably less compressible, stiffer and stronger. The mechanical behavior of natural sedimentary clay clay is different from the comparable behavior of the reconstituted sample as the consequence of structuration induced over the geological period due to natural conditions or rather quickly due to the addition of chemical bonding in fabrics. In this paper, the mechanical behavior of such "structured" clays as highlighted by reduced compressibility, higher stiffness and higher strength was carefully examined in the laboratory.In comparing the elastic shear modulus at very small strains, G between each structured clay and the reconstituted sample, the clay structure was evaluated quantitatively by metastability index MI(G) proposed by Shibuya (2000). The stress-strain and strength behavior when subjected to undrained shear in compression was also simulated by the so-called super/subloading yield surface (SYS) Cam clay model proposed by Asaoka et al. (2000, 2002).