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# Seismic

For the pseudo-static seismic load option, how is the seismic force applied to the model?

If seismic coefficients are defined, a seismic force will be applied to each slice as follows:

Seismic Force = Seismic Coefficient * Slice Weight

= Seismic Coefficient * area of slice * Unit Weight of slice material

Note that the acceleration due to gravity (g = 9.81 m/s2 for metric units) is already incorporated into the material Unit Weight entered in the Define Material Properties dialog (remember that the dimensions of Unit Weight are kN / m3), and therefore does not explicitly appear in the above equation.

The seismic force is applied through the centroid of each slice.

For the pseudo-static option, what earthquake load coefficient should I use for seismic analyses in Slide2?

There are a number of papers and sources for how to determine the seismic coefficient in slope stability analyses. For example, the Hynes-Griffin and Franklin paper recommends a seismic coefficient equal to 0.5*PGA (peak ground acceleration). As well, the Open Pit Slope Design book by Read and Stacey provides a chart for converting PPV to seismic coefficient.

The following references are recommended:

Hynes-Griffin, M. E., and Franklin, A. G. 1984. ‘‘Rationalizing the Seismic Coefficient Method.’’ U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi, Misc. Paper GL-84-13.

Baker, R., Shukha, R., Operstein, V., and Frydman, S. "Stability charts for pseudo-static slope stability analysis." Soil Dynamics and Earthquake Engineering. 26(9): 813-823.

Woodward, P. K., and Griffiths, D. V. 1996. "Comparison of the pseudo-static and dynamic behaviour of gravity retaining walls." Geotechnical and Geological Engineering. 14: 269-290.

Read, J., and Stacey, P. F. 2009. "Guidelines for Open Pit Design." CSIRO Publishing, Melbourne.