Importance of the simple shear loading direction to the stability of tailings

Stability of tailings dams and tailings run-out

David Reid

University of Western Australia

The engineering properties of soils and tailings often exhibit significant anisotropy.  One area where this has been well documents is undrained shear strength.  Materials sheared in directions close to the principal stress direction in situ, i.e. triaxial compression, typically exhibit higher undrained strengths than those sheared in other directions such as simple shear.  Importantly, along the most common critical failure surfaces relevant to tailings stability, whether primarily through tailings or the foundation, saturated materials are generally much closer to the simple shear loading than triaxial compression.  Therefore, testing undrained shear strength of tailings or foundation soils in triaxial compression is likely to result in overestimation of the relevant strengths for design.  Although these issues have repeatedly documented in the geotechnical literature for over three decades, they are not appreciated sufficiently across our industry.  In an attempt to address and highlight these issues, a review is carried out of historical reference to the importance of simple shear loading.  Attention is then drawn to the techniques applied in two recent post-failure investigations, where simple shear testing was applied.  The outcomes of these post-failure investigations and related findings assists in the emphasis on the important of simple shear testing.

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