Study of shear bands and prediction of compaction and failure in the strain localization behavior of geomaterials

摘要：剪切带和滑动面等应变局部化问题非常重要，因为它们是破坏的前兆。因此，许多研究人员在过去的30年里一直在研究。另一方面，为了分析近海结构物的大沉降量，近年来对压实带进行了研究。事实上，关于多孔岩土材料的实验工作早在90年代就已经完成。在排水条件下，对硅藻质多孔岩石进行了一系列三轴压缩试验。采用矩形棱柱试件测量试件表面的应变分布。利用一种新开发的图像分析技术测量了试件表面的局部应变分布，即剪切应变、轴向应变和体积应变。剪切试验后，用X射线CT扫描仪测量试件密度的变化。在围压水平较高的情况下，一些高密度区域与图像分析中观察到的压实带相对应。然后，基于有限变形理论，采用考虑结构退化的弹粘塑性模型对敏感粘土进行了数值模拟，得到了固结过程中的压应变局部化现象。此外，利用该模型进行了软粘土固结的数值模拟和硅藻土质泥岩的排水三轴试验，研究了土工材料的压缩局部化问题，即土工材料的压实带和应变局部化问题。

ABSTRACT: Strain localization problems such as shear bands and slip surfaces are very important because those are precursor of failure. Hence many researchers have been studying for the last 30 years. On the other hand, compaction bands have been studied in recent years for the analysis of large settlement of off shore structures. In fact, experimental work on porous geomaterials has been done from 90s. A series of triaxial compression tests under the drained conditions was performed on diatomaceous porous rocks. A rectangular-shaped prismatic specimen was used to easily measure the strain distributions on the specimen surface. The distributions of local strain, i.e., shear strain, axial strain, and volumetric strain, were measured on the surface of the specimen by using an image analysis technique newly developed for this experiment. After the shear testing, the changes in density of the specimen were measured by an X-ray CT scanner. Some high density regions were found to correspond to the compaction bands observed in the image analysis in the cases of relatively high confining pressure levels. Then, we have carried out a numerical simulation of sensitive clay using an elasto-viscoplastic model with structural degradation based on the finite deformation theory, and we have found the compressive strain localization during the consolidation process. In addition, using the same model, numerical simulations of consolidation of soft clay and drained triaxial tests of diatomaceous mud stone have been carried out to study the compressive localization, namely, compaction bands and strain localization of geomaterials was discussed.