Mechanism of shear band formation in Ko-consolidated clayey soil--experimental and theoretical approaches by naked hollow-cylindrical soil specimen--

本研究的目的是为掌握地基材料的破坏机理提供理论和实验依据。局部变形的发展及其突出可能引起地基失稳，导致地基破坏。这种局部变形在土体的大变形过程中很常见，如实验室观测到的滑移线、路堤基础的滑动破坏、造山运动引起的断层等。通过对剪切带形成过程的模拟，阐明了剪切带现象的发生机制，也为解释土体从变形开始到极限破坏状态的一致行为提供了可能。本文对剪切带形成的分岔问题的理论基础进行了总结和分类。特别讨论了轴对称条件下剪切带形成的数学条件，并与Sekiguchi和Ohta（1977）提出的ko固结黏土试件弹塑性本构模型的非同轴性进行了比较。在试验研究方面，设计并研制了一种新型的剪切试验装置，用于观察轴对称土试件中剪切带随剪切应变的增大而变化。它的显著特点是：1)可以进行ko固结，2)可以测量ko值，3)可以观察剪切带（滑移线）的发展，因为没有使用橡胶膜（裸试样，如无侧限压缩试样），4)可以根据有效应力估计参数，因为可以使用陶瓷盘的负压测量系统来测量孔隙水压力。研究发现，轴对称土样中的视应变-软化应力-应变关系并不是材料的本质现象，而是土样中应力应变分布不均匀的结果，是一个边值问题。少

The purpose of this research is to give theoretical and experimental bases to capture the failure mechanism of the ground material. The development of localized deformation and its prominence may cause the instability of foundation ground and lead to its failure. Such localized deformation is commonly observed during large deformation of soils, for instance, slip lines observed in the laboratory, the sliding failure of embankment foundation and the fault caused by the orogenic movement. The simulation of shear bands formation may lead to clarify the occurrence mechanism of their phenomena and also make it possible to explain the soil behaviors consistently from the beginning of deformation up to the limit failure state.In this research, the theoretical basis of bifurcation problem is summarized and classified in regard to the formation of shear band. In particular, the mathematical conditions of the formation of shear band under axisymmetric condition discussed relating to the non-coax … More iality of the elasto-plastic constitutive model for Ko-consolidated clay specimen proposed by Sekiguchi and Ohta (1977). As to experimental study, a new shear test equipment is designed and developed to observe the development of shear band with increase of shear strain in the axisymmetric soil specimen. The distinctive features of it are : 1) able to carry out Ko-consolidation, 2) able to measure Ko-value, 3) able to observe the development of shear bands (slip lines), because a rubber membrane is not used (naked specimen like the unconfined compression test specimen), 4)able to estimate parameters in terms of effective stresses, because the pore water pressure can be measured using measurement system of negative pressure with the ceramic disk.It was found in this research that the apparent strain-softening stress strain relation in axisymmetric soil specimen is not an essential phenomenum of material but the consequence of inhomogeneous distribution of stress and strain in the specimen as a boundary-value problem. Less