# Geo Struct Sparks LLC

## When Mononobe-Okabe Equation Doesn't Work

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Michael Joseph Kappel
10:31 AM on September 25, 2012
This is a very informative website. I was looking for stuff related to my project when I found it. It is not related but check out my website http://Geotrackable.org
geostructsparks
7:20 AM on December 16, 2011
How would your results differ for a multiple tieback soldier pile wall, with regards to pressure distribution and computing the static active pressure?
[/kevin]

Either WASP or Mononobe-Okabe equation are only for a theoretical soil wedge with no reinforcement. As you are aware, even conventional static tied back wall design involves highly simplified "theoretical" (more like SWAG) distributions of pressure, e.g. back-of-napkin drawings by Terzaghi, and so on. Unless there are finite element or scale model studies in the literature out there, there is no single accepted way to add seismic pressures to a retaining wall. I believe the main approach is to take the same approach as for static walls but increase the active pressure by changing Ka to Kae.

Federal Highway Administration for "restrained" walls (tied back retaining walls, pile-supported abutments and the like, due to the stiffness of the lateral support of the walls), requires that when you consider seismic pressure of one of these, you increase the Kh from 1/2 of the peak ground acceleration for a retaining system free to translate, to 1.5x peak ground acceleration (See Design Examples, US 395 at Plumb Lane). I have read the original commentary that spawned this idea, and while the authors suggested increased Kae by a factor of 3 , that is much less drastic that increasing the input horizontal acceleration by a factor of 3 as adopted by FHWA. The original commentary didn't provide a lot of justification for why this is accurate. For walls with stiff battered pile foundations, this conservatism may make sense; for tiebacks or MSE where the loads are tied back into the material that is providing the inertial load, this seems highly conservative.

(Sorry for the late response, I thought my site notified me by e-mail when comments were added)
Jonathan
usnikkijamesl8
7:16 PM on June 16, 2011
Awesome webpage from Carisa Heuer
kevin
9:15 PM on April 29, 2011
Jonathan
How would your results differ for a multiple tieback soldier pile wall, with regards to pressure distribution and computing the static active pressure?
Dylan
5:40 PM on September 9, 2009
ETA is one month or less!
Eddy
4:34 PM on September 9, 2009
What's the E.T.A. on the software? I have no pressing need but would love to see what you're up to.
Matthew Behling, PE, MBA
7:39 PM on September 8, 2009
Sweet, it's always exciting to learn and utilize a more effective and appropriate methodology for design. Looking forward to seeing the software.
Dylan
12:16 AM on September 7, 2009