Passive Resistance of Berm

[RFreund]

I'm trying to get a preliminary idea on sizes/anchors, etc, for some excavation bracing for an excavation to an existing bluff.
How would you estimate the passive resistance of the berm in front of the sheet piling. This seems to be somewhat debated.
I'd be interested in using both short duration values and long-term effective values (mixed phi-c)?
If I use some sort of effective slope, it exceeds the effective friction angle. The effective soil values are approx phi = 28-32 deg and c= 200-500psf.

Thanks!

EIT

http://www.HowToEngineer.com

 

[oldestguy]

At a Qu at 4 - 5 t/sf, why not just cut back the upper slope to match the original? Assuming the former slope was stable. Driving sheet piles may cause some problems not anticipated.

 

[RFreund]

The slope is suffering due to erosion and they'd like a vertical cut at this location. I believe it may be a permanent sheet piling.

EIT

http://www.HowToEngineer.com

 

[PEinc]

If the existing bluff is fairly stable now, why not just flatten the slope back to the same spot that the top of the sheeting wall would be? First, analyze the existing slope using estimated soil properties to show a safety factor of 1 and then use the same properties to analyze the new, flatter slope.

Also, I would expect a 30' or wider flat area in front of the wall to provide full passive resistance. A tiedback wall would not be the first solution that I would investigate. Will you be able to even drive sheeting that deep into soil that stiff?

http://www.PeirceEngineering.com

 

[RFreund]

Thanks for the additional comments and you have good points (as usual). A few responses:

If the existing bluff is fairly stable now, why not just flatten the slope back to the same spot that the top of the sheeting wall would be?

I believe they want to create a level platform at the new bench elevation.

irst, analyze the existing slope using estimated soil properties to show a safety factor of 1 and then use the same properties to analyze the new, flatter slope.

Good idea. I still need to give this some thought as far as going from a phi-c soil and applying that correctly to find a K.p for the sloped condition.

A tiedback wall would not be the first solution that I would investigate.

Meaning you would try using a cantilever?

Will you be able to even drive sheeting that deep into soil that stiff?

That's a very good question.


EIT

http://www.HowToEngineer.com

 

[PEinc]

Quote (PEinc): A tiedback wall would not be the first solution that I would investigate.

No, not a cantilevered wall. I would consider flatter sloping, maybe soil nailing, or maybe terracing several lower walls with some setback between each level.

http://www.PeirceEngineering.com