Case 1. Loose Sands: Anisotropic Stress-Strain Behaviour
The strength and deformation properties of soils are highly anisotropy. In addition to this inherent anisotropy, many earth structures like soil underneath wind turbines, flood defence fills and some road/rail embankments experience anisotropic loading conditions. This means, the direction of principal stress axes can change and result in stress conditions. Conventional triaxial testing methods fail to simulate these complicated stress-strain behaviour.
The Hollow Cylinder Torsional Apparatus (HCTA) allows an independent control of the magnitude and direction of principal stress axes in conjunction with a measurement of volumetric and pore pressure variations. HCTA facilitates stress path testing by allowing free rotation of principal stress directions (α) and the intermediate principal stress ratio (b), where α is the orientation of the σ1 axis to the vertical, the ratio b is (σ2 − σ3)/(σ1 − σ3), and σ1, σ2, and σ3 are the major, intermediate and minor principal stresses, respectively.
We make use of HCTA to better understand the complicated mechanical behaviour loose saturated sands, and how reinforcement with fibres can improve the overall stability.
Read more: Ghadr, S., Bahadori, H. and Assadi-Langroudi, A., 2019. Anisotropy in Sand–Fibre Composites and Undrained Stress–Strain Implications. International Journal of Geosynthetics and Ground Engineering, 5(3), p.23.