Anisotropy of fibre reinforced sands under generalised loading conditions

地基改善技术广泛应用于基础设施资产(如挡土墙、路堤、基础支撑、人行道和斜坡加固等)，对当前的岩土工程实践具有战略重要性。其中，掺加抗拉纤维的土体加固技术是一种较新的土体加固技术，具有较高的性价比。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理的结果。这种各向异性当然决定了该技术的有效性，在实际应用中，如果不考虑这种各向异性，即使不是灾难性的，也可能是关键的，因为在实际应用中，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研究过，而且仍然没有能够预测其在代表现场条件的加载模式下的行为的模型。因此，这种加固技术的现场应用目前仅限于非常不重要的岩土系统。这项研究将填补现有知识与更广泛和更重要的技术应用需求之间的差距。利用中空圆柱体扭转仪(HCTA)对复合材料的各向异性进行了实验研究，该仪器具有在广义多轴应力空间施加各种加载条件和模拟实际岩土系统加载条件的独特自由度。根据试验结果，建立了纤维加筋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来进行涉及纤维加筋土的岩土系统的安全设计。事实上，任何纤维增强土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.