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

软质半岩的变形包括脆性破坏和延性流动，两者包括中间形式是在剪切的同时发生的。在本研究中，对变形样式的临界条件进行了实验检验，得到以下结果：(1)疏松和半固结粘土单轴压缩剪切面特征存在明显差异，疏松粘土剪切面较薄且已愈合，原生粒构扰动较小，而半固结粘土剪切面主要发育在主剪切面周围。(2)开发了平面应变压缩变形破坏过程中局部剪切应变的可视化技术。(3)从应变局部化的角度对剪切作用下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/或蒙脱石含量较高的粘土，可能会发生滑移破坏后的应变局部化，而对于其他情况，塑性（流动）变形仍然伴随着滑移破坏。(4)通过系统实验研究了应变率和各向异性织物对变形方式的控制作用，发现高应变率下的韧性应力-应变行为、广泛的剪切应变和流动表现优于颗粒-织物。(5)采用应变局部化的物理模型解释了其机理。(6)然而，快速剪切作用下预期的高孔隙压力难以在实验室验证，并且仍然没有解决。

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.