Modelling of the induced and inherent anisotropy of sand

无粘性土的应力-应变特性主要受两种各向异性的影响：在土的初始沉积过程中形成的固有各向异性，即颗粒骨架的初始组构；在材料加载过程中产生的诱发各向异性。不同的土壤形成/放置方法(例如，土地复垦项目的沙浆排放和水下沉积，或露天矿从较高高度倾倒湿材料)导致材料固有的不同各向异性。实验室测试表明，材料行为强烈依赖于固有的和诱导的各向异性，特别是对于土地开垦或露天矿典型的松散沙子。在破坏分析或变形预测中，这种对各向异性的依赖是不能忽略的。遗憾的是，通常使用的本构模型没有考虑织物效应。该项目的主要目的是扩展一种新的粒状土的亚塑性模型，以便同时考虑固有各向异性和诱发各向异性的影响。为此，该模型结合了两个张量，描述了材料的诱导和固有各向异性。扩展模型将根据对不同方法制备的砂样进行的实验室测试进行修改和校准，即它们表现出不同的固有各向异性。利用本项目开发的本构模型，可以模拟织物或预压效应非常重要的边值问题。

The stress-strain behavior of non-cohesive soils is significantly influenced by two types of aniso-tropies: the inherent anisotropy, i.e. the initial fabric of the grain skeleton, which is formed during the initial deposition of the soil, and the induced anisotropy which is generated during the loading of the material. Different formation/placement methods of the soil (for example, sand slurry discharge and under water sedimentation for land reclamation projects or wet material dumping from a greater height in open pit mines) lead to different inherent anisotropies in the material. Laboratory tests show a strong dependence of the material behavior on the inherent and induced anisotropy, in particular for loose sand which is typical for land reclamation or open pit mines. This dependence on anisotropy cannot be neglected in failure analysis or deformation prediction. Unfortunately, the constitutive models commonly used do not consider fabric effects. The main objective of this project is to extend a novel hypoplastic model for granular soils in order to incorporate the effects of both the inherent and the induced anisotropy. For this purpose, the model incorporates two tensors, describing the induced and inherent anisotropy of the material. The extended model will be modified and calibrated based on laboratory tests performed on sand specimens prepared by different methods, i.e. they present different inherent anisotropy. With the constitutive model developed in this project, it will be possible to simulate boundary value problems in which fabric or preloading effects are of significant importance.