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.
Case 1. Loose Sands: Steady States and Microstructure
Poor surficial drainage in sandy hillslopes can lead to flow of silt-bearing waters, abrupt change to the stress state of shallow silty sands and subsequent piping, liquefaction and debris flow. The mechanical behaviour of silty sands is structure-dependent. This is due to their characteristic bi-modal quality of pore and particle size distribution. To gain a better understanding of flow mechanisms, idealized scale-dependent porosity indices are used to build a conceptual micromechanical model that offers an explanation to the complicated undrained stress-strain behaviour at Steady States of sand-silt mixtures as an example of geocomposite materials.
Read more: Ghadr, S. and Assadi-Langroudi, A., 2019. Effect of Grain Size and Shape on Undrained Behaviour of Sands. International Journal of Geosynthetics and Ground Engineering, 5(3), p.18.