Representative Elementary Volumes of coarse-grained soils

粗粒土的代表性基本体积

• 批准号: 508562211
• 负责人: Professor Dr.-Ing. Ivo Herle
• 金额: --
• 依托单位: Professur für Bodenmechanik und Grundbau
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/508562211?language=en
• 关键词: Representative; Elementary; Volumes; coarse; grained

Standard laboratory tests, such as the triaxial test, are commonly used to calibrate the constitutive models aiming to correctly describe the soil behaviour. In order to obtain true material behaviour, those tests are designed and assumed to be element tests. The specimen is considered to be a representative elementary volume (REV), i.e. an element with homogeneous properties and homogeneous behaviour, representing the soil behaviour and is therefore interpreted as a material point. This is obviously not true for the triaxial test where shear banding is usually visible to the naked eye or complex patterns of shear bands form inside the specimen leading to a highly heterogeneous response from very early on.These obvious discrepancies between the phenomena observed in laboratory tests and the assumption of homogeneity forming the basis for the experimental evaluations, the constitutive model calibration and the description of the soil behaviour have to be resolved. The specimen is, in fact, not a single REV but rather consists of multiple REVs, each representing a certain region inside the specimen. The size of such a REV depends on the internal length scales, e.g. the particle size or the shear band thickness, governing the global behaviour. The REV size was also found to depend on the analysed variable, e.g. the void ratio or the contact fabric.Based on the analysis of x-ray computed tomographies (CTs) acquired during the loading of a specimen, we have developed an approach for the determination of the REV size considering three different criteria. This approach will now be used to characterize the different influences on the REV size and to identify the heterogeneous state of the specimen throughout loading. Using x-ray CT for this study, one is limited to the fabric and kinematics of the soil. Ultimately, we want to connect the REV behaviour to the globally observed one characterised by a stress-strain-relationship measured at the boundary of the specimen.At the micro-scale, we also need to include the stresses, which cannot be obtained with x-ray CT. For such a complete description, the discrete element method (DEM) can be introduced. Combining the experimentally and the numerically obtained evolution of the REVs will offer the fundamentals for a comprehensive comparison between the global and the local behaviour. The study of the soil heterogeneity also allows for its incorporation in finite element models and an enhancement of the constitutive model calibration. The consideration of a realistic initial state has already been shown to improve the model calibration. Constitutive models could even be calibrated for chosen REVs, e.g. those inside the shear band, which have been assumed to be the only ones reaching a true critical state. The results of these investigations will form the basis for a link between conventional assumptions and evaluations on the one hand and micro-scale observations and phenomena on the other hand.

标准实验室测试（例如三轴测试）通常用于校准本构模型，旨在正确描述土壤行为。为了获得真实的材料行为，这些测试被设计并假设为元素测试。样本被认为是代表性单元体积（REV），即具有均匀属性和均匀行为的单元，代表土壤行为，因此被解释为质点。这对于三轴试验显然是不正确的，因为剪切带通常是肉眼可见的，或者样本内部形成复杂的剪切带图案，从而从很早开始就导致高度不均匀的响应。实验室试验中观察到的现象与构成实验评估、本构模型校准和土体行为描述基础的均匀性假设之间的这些明显差异必须加以考虑。 解决了。事实上，该样本不是单个 REV，而是由多个 REV 组成，每个 REV 代表样本内的某个区域。这种 REV 的大小取决于内部长度尺度，例如颗粒尺寸或剪切带厚度，控制整体行为。还发现 REV 大小取决于分析的变量，例如基于对样品加载过程中获得的 X 射线计算机断层扫描 (CT) 的分析，我们开发了一种考虑三种不同标准来确定 REV 尺寸的方法。现在，该方法将用于表征对 REV 尺寸的不同影响，并确定样品在整个加载过程中的异质状态。这项研究使用 X 射线 CT，但仅限于土壤的结构和运动学。最终，我们希望将 REV 行为与全局观察到的行为联系起来，该行为以在样本边界测量的应力应变关系为特征。在微观尺度上，我们还需要包括应力，这是 X 射线 CT 无法获得的。对于这样的完整描述，可以引入离散元法（DEM）。结合实验和数值获得的 REV 演化将为全局和局部行为之间的全面比较提供基础。对土壤异质性的研究还可以将其纳入有限元模型并增强本构模型校准。考虑实际初始状态已被证明可以改进模型校准。本构模型甚至可以针对选定的 REV 进行校准，例如剪切带内的那些，被认为是唯一达到真正临界状态的。这些调查的结果将成为传统假设和评估与微观观察和现象之间联系的基础。