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Seismic Loading

The Seismic Loading option in the Loading menu allows you to include the effect of pseudo-static earthquake loading in the limit equilibrium analysis.

To define Seismic Load:

  1. Select the Loading & Support workflow tab loading and support workflow tab icon
  2. Select Loading > Seismic Loading seismic loading icon
  3. In the Seismic Loading dialog:
    • Set the Orientation. The options for defining the orientation are described below.
    • Enter the seismic load Coefficient(s) as described below.
    • Click OK.
Seismic Loading Dialog
Seismic Loading Dialog


There are three options for defining the Orientation of a pseudo-static Seismic Load:

  • Sliding Direction - the direction of applied seismic loading is in the same direction as the sliding direction of the block.
  • Trend/Plunge - specify the 3D orientation of a seismic load by entering Trend and Plunge angles.
    • Trend is measured in degrees clockwise from the north direction (north = the Y-axis of the model).
    • Plunge is measured from the horizontal, with a positive down convention.
    • The seismic load Coefficient is applied in the Trend/Plunge direction.
  • Vector - specify the 3D orientation of a seismic load in terms of X, Y, Z components. The seismic load coefficient is applied in the Vector direction.

Seismic Coefficient

The seismic Coefficient(s) are dimensionless coefficients which represent the (maximum) earthquake acceleration as a fraction of the acceleration due to gravity. Typical values are in the range of 0.1 to 0.3.

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

Seismic Force = Seismic Coefficient * Block Weight = Seismic Coefficient * Block Volume * Unit Weight of Material

The seismic force is applied through the geometric centroid of each block, according to the selected Orientation method as described above.

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 Materials dialog (the dimensions of Unit Weight are force/volume), and therefore g does not explicitly appear in the above equation.
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