Liquefaction behaviour of tailings under cyclical simple shear testing

Mine waste geotechnics, geochemistry and biology


Allen Li


GHD

The behaviour of the tailings under cyclic loadings will have an impact on the stability and deformations of tailings dams and a good understanding of the cyclic behaviour of the tailings under earthquakes is important for tailings engineers and tailings operators for the design and safe operation of tailings dams.  This paper presents an investigation into the cyclic behaviour of tailings using both laboratory cyclic direct simple shear (DSS) testing and numerical modelling.  The laboratory testing involved cyclic DSS tests on gold tailings and zinc and copper tailings under different loading densities and loading frequencies.  The gold tailings specimen tested at a higher loading frequency and a higher cyclic stress ratio experienced spontaneous liquefaction during cyclic shearing and the zinc/copper tailings specimen tested at a lower loading frequency and a similar cyclic stress ratio exhibited ductile behaviour and liquefied due to cyclic mobility.

The liquefaction behaviour of the tailings was modelled using an advanced constitutive model (UBCSAND), which was developed specifically to model soil liquefaction and strain softening under cyclic loadings.  The constitutive soil model presents the nonlinear soil behaviour under dynamic loadings using a hyperbolic stress-strain relation.  Dynamic analyses were carried out using a finite difference program FLAC.  The cyclic stress-induced excess pore water pressures measured in the laboratory were modelled using numerical simulations of the laboratory tests under different loading conditions.  The results of the non-linear dynamic analyses demonstrated the capability of numerical modelling of cyclic shearing induced excess pore water pressure and the onset of the spontaneous liquefaction.  The laboratory investigation and numerical modelling technique provided the key properties and parameters for the dynamic analyses to assess the stability and deformation of tailings dams under the design earthquake events.  More importantly, the laboratory tests and numerical modelling provided some insights into liquefaction behaviour of the tailings during earthquakes.

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