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

软半实物的变形包括脆性破坏和韧性流动，两者包括中间型，同时发生剪切作用。(1)松散粘土和半固结粘土在单轴压缩下的剪切面特征表现出独特的差异，即松散粘土的剪切面较薄，一次颗粒组构的扰动较小，而半固结粘土的二次剪切主要集中在主剪切面附近。(2)研究了平面应变压缩变形破坏过程中的局部剪切应变可视化技术。(3)从应变局部化的角度对剪切作用下的滑移破坏与塑性流动变形的相互关系进行了分类，对于岩化程度较高和/或富蒙脱石的粘土，滑移破坏后可能发生应变局部化，对于其他情况，塑性流动变形仍然伴随滑移破坏。(4)通过系统的实验研究了应变速率和各向异性组构对变形方式的控制作用，发现在高应变率下表现出延性的应力应变行为、大范围的剪切应变和流动，这比颗粒组构更有效。(5)用考虑应变局部化的物理模型对其机理进行了解释。(6)快速剪切作用下的高孔压难以在实验室验证，仍未得到解决。

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.