Anisotropy of fibre reinforced sands under generalised loading conditions

地基加固技术广泛应用于基础设施资产（例如挡土墙、护坡、地基支撑、路面和斜坡稳定等），对当前的岩土工程实践具有战略重要性。其中，将土壤与抗拉纤维混合是一种相对较新的土壤加固技术，可以代表大量应用的具有成本效益的解决方案。纤维的增强效果是高度各向异性的，这是由于所采用的混合和压实过程引起的优先层积。这种各向异性当然决定了该技术的有效性，在真实的应用中，如果不是灾难性的，忽略它也是至关重要的，在这些应用中，主应力和应变轴的旋转几乎总是发生在土体中。然而，这种材料的各向异性从来没有被调查和一个模型，能够预测其行为下的负载模式代表现场条件仍然是不可用的。因此，这种加固技术的现场应用目前仅限于非常次要的岩土系统。这项研究将填补当前知识与该技术更广泛和重要应用的需求之间的差距。复合材料的各向异性将通过使用空心圆柱扭转装置（HCTA）进行实验研究，该装置具有独特的自由度，可以在广义多轴应力空间中施加各种载荷条件，并模拟真实的岩土系统。基于试验结果，提出了一种新的纤维增强土在多轴应力空间中的各向异性本构模型。新的模型将允许使用数值分析的安全设计的岩土工程系统，包括纤维增强土壤。事实上，任何纤维增强土壤系统的设计都将始终受到材料各向异性的影响。

Ground improvement technologies are extensively applied within the infrastructure asset (e.g. retaining walls, embankments, foundations support, pavements and slopes stabilisation among others) and they have a strategic importance for the current geotechnical practice. Among them, mixing soils with tensile resistant fibres is a relatively new soil reinforcing technique which can represent a cost-effective solution for a large number of applications. The reinforcing effect of the fibres is highly anisotropic as a result of the preferential bedding induced by the mixing and compaction processes employed. This anisotropy certainly dictates the effectiveness of the technique and its disregard can be critical, if not catastrophic, in real applications where rotation of the principal stresses and strains axis almost invariably occurs within a soil mass. However, the anisotropy of this material has never been investigated and a model which is able to predict its behaviour under loading modes representative of field conditions is still not available. It follows that the field application of this reinforcing technique is currently limited to geotechnical systems of very minor importance. This research will fill the gap between current knowledge and the needs for more extensive and important application of the technique. The anisotropy of the composite material will be experimentally investigated by using the Hollow Cylinder Torsional Apparatus (HCTA), which possesses a unique freedom to impose a variety of loading conditions in the generalised multiaxial stress space and simulate those of real geotechnical systems. A new anisotropic constitutive model for fibre reinforced soils in the multiaxial stress space will be developed based on the experimental findings. The new model will allow the use of numerical analyses for the safe design of geotechnical systems involving fibre reinforced soils. Indeed, the design of any fibre reinforced soil systems will be invariably governed by the anisotropy of the material.