Experimental Study on Brittle - Ductile Transition in Shear Deformation of Soft Sediments

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Deformation of soft-semidents involves brittle failure and ductile flow, both of them including intermediate style occur at the same time of shearing. In this study, critical condition for deformation style was examined experimentally, and following results were obtained ; (1) Shear plane characteristics under uniaxial compression for unconsolodated and semi-consolidated clay show particular differences, such as thin and healed shear plane with less disturbance of primary grain-fabric for unconsolidated clay, while dominant secondary shear developed around the main shear plane for semi-consolidated clay. (2) Visualization technique for local shear strain during deformation and failure by plane-strain compression was developed. (3) Interrelationship between slip failure and plastic flow deformation under shear was categorized from the standpoint of strain-localization ; slip failure followed by strain-localization is likely to occur for more lithified and/or smectite-rich clay, plastic (flow) deformation is still accompanied with slip failure for the other case. (4) Strain-rate and anisotropic fabric as control factors on deformation style were investigated by systematic experiments, and ductile stress-strain behavior, extensive shear strain and flow were shown under high strain-rate, which is more effective than grain-fabric. (5) Its mechanism was explained by physical model involving strain-localization. (6) High pore-pressure expected under rapid shear is, however, difficult to verify in laboratory, and is rmained unsolve.