Liquefaction assessments of tailings facilities in low-seismic areas

 

It is widely recognised that piezocone (CPTu) testing is a valuable technique for identifying the in situ engineering properties of tailings for use in stability and liquefaction assessments. Numerous empirical

procedures have been developed to relate the results of piezocone testing to liquefaction potential. Appropriate assessments are particularly important for upstream raised tailings facilities which have an inherently higher risk of failure due to liquefaction following seismic events.

 

This paper evaluates two commonly used procedures developed by Robertson (2010), and Idriss & Boulanger (2008) for determining

liquefaction potential. These procedures calculate the factor of safety against liquefaction by comparing the cyclic resistance ratio (CRR) to the seismically induced cyclic stress ratio (CSR). During the design of an upstream raise to a tailings facility in Western Australia, it was found that Robertson’s approach leads to improved estimates of the CRR by considering the influence of fines content. Idriss & Boulanger’s recommendation of a cut-off value for earthquake magnitude scaling factors and magnitude-dependent stress-reduction coefficients offers a more conservative estimate of the CSR, particularly where the design earthquake magnitude is less than 7. The case study identified a gap between the methodologies for assessing the liquefaction potential for tailings facilities in areas with low seismicity that requires further research.