Retaining wall in slopes

[Okiryu]

Hi, perhaps this is a basic question but, why the failure plane of the slope always pass thru the wall heel for slope stability analysis in cantilever concrete retaining walls? I was thinking on that but cold not find a good answer. If this is for fill areas, I can see that perhaps the failure plane "follows" the plane between the existing and fill soils behind the retaining wall and therefore the failure plane touches the wall heel. But I am not sure if this is correct...

 

[GeoPaveTraffic]

The failure plane does not always pass through the heel, but it usually does. It is just a mater of the forces. Best suggestion is for you to set up a simple stratigraphy and geometry and then play with different soil parameters. If you do enough different runs, you will find cases where the failure plane doesn't pass through the heel.

Mike Lambert

 

[Doctormo]

Pretty hard to have a failure plane through reinforced concrete thus the path of lease resistance is around the concrete wall and what slope stability programs will seek out for the lowest factor of safety.

There may be some configurations like Mike mentions above where the failure plane goes further below a concrete wall but that requires less than uniform soil conditions and almost a special case situation. Generally, if the failure plane does not go right around the heel, I think the modeling is suspect and that the search limits need to be reviewed.

 

[Okiryu]

Mike and Doctormo, thanks for the replies which make sense to me. I was just asking this question because I was using the Bowles book to check some retaining wall design and found that Bowles mentions that the all failure planes pass through the heel point. See attached.

 

[GeoPaveTraffic]

Remember this is a text book discussing principals and talking about doing the analysis by hand. The vast majority of failures will go through the heel, just don't be surprised that there will be exceptions if you look at enough different situations.

Mike Lambert

 

[Okiryu]

Mike, understood and thanks again for the warning note.

 

[PEinc]

There is a big difference between the failure surface passing "through the heel" (i.e., through the back of the concrete footing) and passing through the "heel point" (just passed the end of the concrete footing as shown by Bowles).

http://www.PeirceEngineering.com

 

[Okiryu]

PEinc, yes, you are right, I did not explain it well in my first post... sorry for the confusion.

 

[BigH]

Also - the "failure" plane you are talking about is the "Wall Failure" plane for determining overturning, sliding. May not be the same as the "real" failure plane in a global stability analysis.

 

[Okiryu]

BigH, based on Bowles book, I was thinking that was the plane failure for global stability. In order to determine the wall dimensions, I checked for sliding, overturning and bearing capacity separately. Once I determine the dimensions based on the above separate analysis , I can check for global stability based on those dimensions. Is this not correct?