Retaining Wall - Overturning Moments

[slickdeals]

Folks,
See attached sketch. I have a situation where the footing needs to be founded at 2m below the Existing Ground Level (left side). The right side is backfilled to 4.2m elevation. I don't want to extend the wall all the way to the bottom if I can avoid it.

However, how do I account for the overturning moment due to this partial height retaining element?

 

[Teguci]

Using active pressure, calculate the soil pressure on the wall and transfer that pressure laterally to the columns. Design the columns for the appropriate lateral loads and consequent overturning.

 

[slickdeals]

Thanks, I wanted to confirm that I could use the active pressure calculated using a triangular distribution based on the height = the height of the wall.

 

[slickdeals]

Sorry to bump this thread up again, but is the lateral earth pressure calculated based on the height (H) calculated from the heel?

Only a portion of this earth pressure actually retained (equal to height of wall) will be transferred to the column, at its appropriate Height (H/3 from the bottom of the wall).

 

[hokie66]

The moment on the column varies. It is one value at the bottom of the wall, and a greater value at the footing. You would get little assistance from passive pressure because the column is not very wide, so I would ignore that.

 

[slickdeals]

Thanks Hokie. Yes, you are right about the column moments. What I was saying is that the cantilever moment at the base of the column will be evaluated with a moment arm = (h/3 above the bottom of the wall) + height of column below the wall.

Are we saying the same thing?

You are right above passive pressure, I am not counting on it.

The only issue I see is that this system leaves no room for any excavation on the non-retained side.

This may just end up being an academic study, but I wanted to make sure I got the right concept.

 

[ToadJones]

I supposes this is no different than any other retaining wall.
I guess you could just take one column and the tributary width and analyze that.

 

[azcats]

Silly question here, but what keeps the soil on the high side from 'flowing' under the wall to the low side? Is there enough difference between the active pressure on the high side and passive pressure on the low side?

 

[dcarr82775]

Azcats,

Typically the soil will not flow under the wall. The mechanism where this would occur is a bearing capacity failure of the the soil on the low side. This typically is a problem with softer clays and a deeper excavation

 

[msquared48]

If you are placing a free-draining gravel backfill behind the wall, there will be weeping at the base of the wall, and in the event of an earthquake, a possible tendency for the material at the base of the wall to liquefy.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

slickdeals,

Yes, that is what I meant.

 

[bgatto]

Active pressure acting right to left, passive pressure acting left to right. The passive pressure could be considered as spring support.

 

[Teguci]

This is almost a sheeting and shoring kind of design. (Auger a caisson into the ground attach a Wide flange column and install precast wall between columns)

The soil pressure is calculated from the top of retained soil. It doesn't much care whats below it just whats pushing down on it.