2012 – Assessment of Liquefaction-induced Deformation of Tailings Dams using Effective Stress Analysis Approach

Hendra Jitno

The design of tailings dams under earthquake loading is quite challenging due to the nature of the tailings materials which are generally liquefiable under earthquake shaking. The design will be more complicated when the dam foundation is also liquefiable material. While assessment of liquefaction potentials is well developed in practice, assessment of liquefaction induced deformation varies from the simplest Newmark’s displacement method to the more complex effective stress dynamic analysis approach. It is generally accepted that the simplified method can be used for cases involving non-liquefiable materials. However, the use of this method for cases involving liquefaction may generally result in overly conservative designs to cater for the many simplified
assumptions in the method. With the advance of computer technology, time and cost are no longer obstacles for using the more appropriate method for estimating liquefaction-induced deformations of a tailings dams and achieving an optimum dam design.

This paper attempts to critically discuss issues in seismic design of tailings dams and provide an example of the use of the effective stress dynamic analysis method to estimate the liquefaction-induced deformations of a tailings dam and its importance in optimizing the design. The approach used is capable of estimating pore pressure response of liquefiable materials at any given time during the shaking. The effective stress analysis method used herein is embedded in FLAC software using a specially written FISH routine. Using this method, it can be demonstrated that although liquefaction is an issue, it does not necessarily mean that we must prevent its occurrence. As long as the deformation is acceptable, liquefaction is not necessarily a ‘show stopper’ for the project.

Keywords: liquefaction, seismic deformation, tailings dam design.

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