Fibre orientation in fibre-reinforced sand (FRS) is highly anisotropic due to compaction during sample preparation or field construction. This makes the mechanical behaviour of FRS, such as strength and dilatancy, highly dependent on the strain increment direction. While constitutive models that are able to capture such anisotropic behaviour of FRS have been proposed for conventional triaxial compression and extension conditions only, this paper proposes for the first time a full anisotropic model for FRS formulated in the general multiaxial stress space. The new model is developed based on the assumption that the strain of FRS is dependent on the deformation of the sand skeleton. In turn, the fibre presence affects the void ratio and effective stress of the soil skeleton, which governs the elastic properties, dilatancy and plastic hardening of the FRS. The effect of anisotropic fibre orientation on the FRS behaviour is considered through an anisotropic variable which characterises the relative orientation between the loading direction tensor and fibre orientation tensor. The model does not require direct measurement of the stress–strain relationship of individual fibres. Although the model is for FRS under multiaxial loading conditions, the parameters associated with the fibre inclusion can be determined based on triaxial test results, provided that the orientation of fibres is known. The model has been used to predict the stress–strain relationship of fibre-reinforced Hostun RF (S28) sand under multiaxial loading conditions. Satisfactory agreement between the experimental data and model predictions is observed.

中文翻译：

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纤维增强砂的多轴本构模型

由于样品制备或现场施工过程中的压实，纤维增强砂（FRS）中的纤维取向高度各向异性。这使得FRS的机械行为（例如强度和膨胀率）高度依赖于应变增量方向。虽然仅针对常规三轴压缩和扩展条件提出了能够捕获FRS各向异性行为的本构模型，但本文首次提出了在一般多轴应力空间中公式化的FRS完整各向异性模型。基于FRS的应变取决于砂骨架变形的假设，开发了新模型。反过来，纤维的存在会影响土壤骨架的空隙率和有效应力，从而决定了弹性，FRS的膨胀性和塑性硬化。通过各向异性变量考虑各向异性纤维取向对FRS行为的影响，该变量表征了加载方向张量和纤维取向张量之间的相对取向。该模型不需要直接测量单个纤维的应力-应变关系。尽管该模型适用于多轴载荷条件下的FRS，但只要已知纤维的取向，就可以基于三轴测试结果确定与纤维夹杂物相关的参数。该模型已用于预测多轴载荷条件下纤维增强的Hostun RF（S28）砂的应力-应变关系。观察到实验数据和模型预测之间令人满意的一致性。通过各向异性变量考虑各向异性纤维取向对FRS行为的影响，该变量表征了加载方向张量和纤维取向张量之间的相对取向。该模型不需要直接测量单个纤维的应力-应变关系。尽管该模型适用于多轴载荷条件下的FRS，但只要已知纤维的取向，就可以基于三轴测试结果确定与纤维夹杂物相关的参数。该模型已用于预测多轴载荷条件下纤维增强的Hostun RF（S28）砂的应力-应变关系。观察到实验数据和模型预测之间令人满意的一致性。通过各向异性变量考虑各向异性纤维取向对FRS行为的影响，该变量表征了加载方向张量和纤维取向张量之间的相对取向。该模型不需要直接测量单个纤维的应力-应变关系。尽管该模型适用于多轴载荷条件下的FRS，但只要已知纤维的取向，就可以基于三轴测试结果确定与纤维夹杂物相关的参数。该模型已用于预测纤维增强的Hostun RF（S28）砂在多轴载荷条件下的应力-应变关系。观察到实验数据和模型预测之间令人满意的一致性。