Direction of seismic loads and the need for seepage analysis prior to stability analysis

AshishKumarRoshan
AshishKumarRoshan Posts: 2
in GeoStudio

For the stability analysis of embankment dam, what should be the direction of horizontal and vertical seismic coefficient.

1.What is the meaning of a positive and negative coefficient for both vertical and horizontal case?

2. For eg. for the stability analysis of embankment dam for d/s slope what should be the sign for the values of seismic coefficient (vertical/horizontal)?

3. For stability analysis of dam at FRL, is it necessary to do seepage analysis before stability analysis?

And do provide references to your answer, it would be really helpful.

Thanking you in advance.

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Answers

  • KathrynDompierre
    KathrynDompierre Posts: 16 mod

    Hello, the pseudo-static method applies an additional force based on the weight of the slice and the pseudo-static seismic coefficient (as shown below). The seismic coefficient is dimensionless and thus is always positive.

    image.png

    For more information on the pseudo-static method, please see the SLOPE/W course that is available in the Seequent Learning Centre or the Slope Stability Modelling Manual: https://files.seequent.com/GeoStudio/Manuals/Slope%20Stability%20Modeling.pdf

    The need for a seepage analysis depends on how complex the pore water pressures are at your site. If the dam has many layers including filters, core, etc. a seepage analysis is likely necessary to capture the full pore water pressure conditions.

  • AshishKumarRoshan
    AshishKumarRoshan Posts: 2

    Hello Kathryn,

    Thank you for the reply, it was truly helpful.

    I have one more doubt regarding the same.
    "In a 3D stability analysis, the horizontal seismic force is applied on each column in the direction of sliding. In both 2D and 3D, the vertical seismic load is added to the column weight." This is from the manual as per your reference.

    What will happen if I use a negative vertical seismic coefficient. Will that load gets subtracted (-) from the weight or will that load gets added (+) to the weight?

  • KathrynDompierre
    KathrynDompierre Posts: 16 mod

    Hello Ashish,

    A positive k_v results in a downward force, which increases the weight of each column. This can have a counter-intuitive effect. In terms of moment equilibrium, some columns have greater driving moment while others have greater resisting moments. All columns, however, have an increased base normal stress, which will increase the strength (if the material models are effective stress type) and therefore the FoS increases. A negative k_v will have a similar counter-balancing effect on rotations, but will decrease the normal stress, the corresponding strengths, and therefore the FoS.  

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