Evaluation of failure and deformation in alluvial clay deposits during earthquake

虽然对于砂土的液化行为有比较明确的指导原则，但对于循环荷载作用下的粘土，特别是现场条件下的粘土，还需要建立一个类似的知识库。为了这个研究项目的目的，从广岛、横滨、熊本、大分和佐贺采集了薄壁粘土样本。粘土的性质不仅取决于它们的可塑性等特征，还取决于它们的沉积来源、组构和应力路径。在不同的塑性指标、超固结比和围压下，对原状土样进行了一系列循环三轴试验。与对重塑粘土进行的一系列进一步测试相比，这些测试都有很好的效果。建立了循环抗剪强度与塑性指数、覆岩压力、固结屈服应力和超固结比的经验关系式，并对高塑性海相粘土进行了一系列不排水循环三轴压缩试验。在各向同性和各向异性固结试件上使用初始静态和随后的循环剪切应力的各种组合进行测试。首先考虑循环剪切强度，然后研究循环应力峰值处的累积剪应变与有效应力比之间的关系。在试验结果的基础上，提出了一个半经验模型来评价循环加载过程中孔压和残余剪应变的发展。该模型成功地解释了粘土在不同大小的初始静剪应力和随后的循环剪应力作用下的行为。

Although there exists relatively clear guide line on the liquefaction behavior of sands, a similar knowledge base for clays under cyclic loading needs to be developed, particularly for in-situ conditions. For the purpose of this research program thin walled clay samples have been taken from Hiroshima, Yokohama, Kumamoto, Ooita and Saga. The properties of the clays depend not only on characteristics such as their plasticity but also their sedimentary origins, fabric and stress path. A series of cyclic triaxial tests has been performed at varying plasticity indeces, overconsolidation ratios and confining pressures on undisturbed samples. These have heen compared with a further series of tests on remolded clays. As a result we have developed an empirical equation relating cyclic shear strength to the plasticity index, overburden pressure, consolidation yielding stress and overconsolidation ratio.Additionally, a series of undrained cyclic triaxial compression tests has been performed on a high plasticity marine clay. Testing was performed using various combinations of initial static and subsequent cyclic shear stress on isotropically and anisotropically consolidated specimens. The cyclic shear strength was considered first, and then, the accumulated shear strain was investigated related to the effective stress ratio at the peak cyclic stress. Based on the experimental results, a semi-empirical model is proposed for evaluating the development of pore pressure and residual shear strain during cyclic loading. The model successfully explains the behavior of clay subjected to various magnitudes of initial static and subsequent cyclic shear stresses.