Retaing Wall

[cdous]

There is a typical 4m cantilever retaining wall which is back filled 3m thus has a "free-board" of 1m
There is a scenario that water can rise at the side of the back fill up to the wall's crest.
The back fill is relatively permeable. It is clear that the relevant Mononobe Okabe formula will apply for both the soil and water.
Using the Ewd=(7/12)*Kh*γw*H with H=3m
and then Westergraad's formula (7/8)*kh*γw*sqrt(h*z) with h=1 freeboard
Inertia forces will act on the soil mass with weight (γsat-γwater)?

 

[johnbridge231]

and on the wall as well.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[JoshPlumSE]

I'm really just venting here. But, this is a 4 meter wall with only 1 meter difference in the soil on either side, right? This wall is basically embedded in the soil. Won't this wall just move with the earth during the seismic event?

It seems to me that Mononabe-Okabe is crazy conservative in cases like this. I'm seeing more an more engineers designing simple retaining walls for seismic forces like this. Is that because there isn't any other guidance out there, or is it because they really feel like the wall needs to be designed for these kind of forces?

 

[hokie66]

Josh,
I don't know anything about Mononabe-Okabe, but the way I read his post, the wall is 4 metres high above the low side, backfilled 3 metres, leaving a 1 metre "parapet".

 

[JoshPlumSE]

Hokie -

Yeah.... Let me wipe that egg from my face. I don't know how I could have read it the other way.

Reading it the correct way, this is probably one of the few cases where I would agree with Mononabe-Okabe for the calculation of seismic loads. You've got the water pressure on one side vs the other. That can be problematic during a seismic event.

But, if you take the water away, my previous comment still holds to some degree. I'm seeing a lot of engineers get excited about seismic for retaining walls recently. But, when I was a newbie seismic loads were almost always ignored. That's because the wall was assumed to move with the soil. It's like a foundation with no super-structure. Were there some big failures that I'm not aware of that are causing this new concern?

 

[cdous]

The structure, an inverted frame with "wings" Please see attached pdf.
The structure is located in an area with pga 0.43, hence earthquake loads can not be ignored

 

[cdous]

Please find correct address for attachment.[highlight #FCE94F][/highlight]

 

[FixedEarth]

The seismic earth pressure (applicable only to soil) is 0.375*Kh*Gamma*H^2 and it applies at H/3 above the bottom of the footing. As mentioned earlier, walls designed for static earth pressures and surcharges with adequate safety factors in stability analysis have performed well after a seismic event.

http://www.soilstructure.com/

 

[cdous]

OkEY in applying Seed & Whitman's formula.
You add to your Active Earth Pressure and Hydrostatic the Earthquake augmentation part and the Hydrodynamic
Does Seed and Whitman has the same triangular distribution as Active Earth Pressures;
Inertia of the structure and back fill supported on the footing shouldn;t be ignored,as the design is per Eurocodes.

 

[FixedEarth]

There is a 2013 seismic earth pressure method that supercedes the Seed & Whitman method. You can find it on the 3rd listing of this publications page:

http://www.ce.berkeley.edu/people/faculty/sitar/publications

http://www.soilstructure.com/

 

[cdous]

Much appreciated the info provided about the publications and your posts
Thanks a lot Fixed Earth.