Imperfection-sensitive bifurcation of cam-clay under plane-strain compression with undrained boundaries
Imperfection-sensitive bifurcation of cam-clay under plane-strain compression with undrained boundaries
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不排水边界平面应变压缩下凸轮粘土的缺陷敏感分叉
DOI：
10.3208/sandf1972.35.83
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发表时间：
1995
影响因子：
3.7
通讯作者：
T. Noda
中科院分区：
文献类型：
--
作者：
A. Asaoka;T. Noda
采用土-水耦合有限变形分析方法，模拟了一个矩形（12 cm × 36 cm）Cam-Clay试件在不排水边界面内均质压缩状态下的缺陷敏感性分叉。分析采用非线性有限元法通过一个更新的拉格朗日格式，其中对应于前几个分叉模式的分叉点被发现是很好地近似外载荷的极限点，通过引入余弦曲线的几何缺陷两侧的标本。当考虑快速测试时，这尤其正确。即使在不排水边界条件下，当试件包含初始缺陷时，缺陷也会从一开始就引起孔隙水的迁移。因此，迁移对剪切变形的影响应高度依赖于垂直位移速率。当施加缓慢的位移速率（9.12 × 10-3%/min）时，在本研究中发现，模式转换由于迁移而发生，并且在荷载-位移曲线中出现“峰值”，这自然产生相对较低的不排水剪切强度。饱和粘土的不排水剪切强度的这种速率依赖性的可能原因之一是归因于孔隙水迁移的影响上的阻尼敏感的分叉行为的饱和粘土。
Imperfection-sensitive bifurcation of a rectangular (12 cm × 36 cm) Cam-Clay specimen emerging from a state of homogeneous in-plane compression with undrained boundaries is simulated by soil-water coupled finite deformation analysis, in which the vertical displacement at a constant rate is imposed on the top of the specimen. The analysis is carried out using a non-linear finite element method through an up-dated Lagrangean scheme, in which the bifurcation points corresponding to the first few bifurcation modes are found to be well approximated by the limit points of external load by introducing cosine-curve geometrical imperfection on both sides of the specimen. This is particularly true when a fast rate of testing is considered. Even with undrained boundaries, when the specimen includes initial imperfection, the imperfection causes the migration of pore water from the beginning. The effect of migration on the shear deformation, therefore, should be highly dependent on the rate of vertical displacement. When a slow rate of displacement (9.12 × 10-3%/min) is applied, it is found, in this study, that the mode-switching occurs due to migration and a "peak" in the load-displacement curve occurs which naturally yields a relatively low undrained shear strength. One of the possible reasons for this rate dependency of undrained shear strength of saturated clay is ascribed to the effect of pore water migration on the imperfection-sensitive bifurcation behaviour of saturated clay.