RETAINING WALL - Overturning moment and Soil weight participation

[adelz]

Hi,

When I look into Overturning stability for Retaining walls, I see that the weight of concrete, other weights above it and the soil above the footings are considered for countering the Overturning moment.

I wonder if it would be acceptable to also consider the soil above the footings in projection of a value equal to the soil friction angle. It makes sense to me, but I can't find a reference on it.

Thanks for replies.

 

[SlideRuleEra]

I wonder if it would be acceptable to also consider the soil above the footings in projection of a value equal to the soil friction angle.

At what depth below the surface does the soil "rupture" because of uplift from resisting overturning, making the friction angle meaningless? A few inches? A few feet?

If the depth can be conservatively defined for all possible conditions (wet, dry, etc.), then I suppose the friction angle can be (partially ) taken into account.

 

[le99]

You shall review the "trail wedge" method in determining earth stability. But in general, don't mess with the analysis of the earth retaining structures, for which uncertainty is high, and human lives and property losses are often at stake.

 

[BridgeSmith]

It's not acceptable under the AASHTO specifications. It has diagrams that show the soil load on the footing ending at a vertical line at the back of the footing.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[EireChch]

I agree with lee99, although it is adding some resistance , I wouldn’t consider due to to the risks associated with failure

 

[JoshPlumSE]

I've never considered any soil that wasn't directly over the footing to participate in uplift or sliding resistance. I suppose there could be some resistance, but I would never rely on it unless I got a soils report from a licensed geotech that specifically told me to do so for this particular project.

 

[ATSE]

The CRSI method accounts for added soil resistance via friction along a vertical plane at the heel (good, bad, or indifferent).

 

[BridgeSmith]

The CRSI method accounts for added soil resistance via friction along a vertical plane at the heel

Now that you say that, I realize AASHTO does the same. The retained soil pressure is applied at an angle, which we apply as a horizontal component and a vertical component.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[adelz]

I see that it is not written to take into account, but this is the point for this thread... Friction angle is a reality and until it starts moving, it can participate - I think. I'll talk to a Professor about that.

 

[le99]

The reason you can't rely on the internal friction angle is simply that it is not reliable. Remember it can be reduced/lost completely in certain cases.