Surcharge Load on Retaining Wall

[Engrman]

Does anyone have a procedure for determining the effects on a cantilevered retaining wall from a concentrated surcharge load on the fill side, including increased active pressure on wall and impact on footing bearing pressure? I have two methods from different sources and neither agree with the other.

 

[aggman]

I use the procedure in Peck, Hanson, and Thornburn to account for the effects but I have found it to be somewhat confusing. I also use Geotechnical Engineering by V.S. Murthy. The Murthy book has the equations, which can also be found in the Bowles book, and shows the vertical and horizontal pressure distribution. I believe the formula's are all based on Boussinesq theory. What I have found in the past is that sometimes you are better off to have a slab which can distribute the loads over a larger area and reduce wall stresses.

 

[aggman]

You may also find this link tells you what you want. It is similar to the mathods I have used. Take a look at Chapter 4.

http://www.vulcanhammer.net/download/dm7_02.pdf

 

[aggman]

Darn engineers and their inability to type fast and spell correctly at the same time! (I meant methods not mathods.)

 

[dicksewerrat]

They misspelll because they think faster than their fingers move.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Engrman]

aggman, thanks for the post. Very helpful. But, mayhaps them flyin' fingers meant to type Chapter 3 instead of 4. Anywho, the method in chapter 3 is identical to one I already have. So that's two against the other one I have and in a democracy the majority rules, right?

 

[jdonville]

Engrman,

The development of active pressure will depend on the movement of the wall. If I recall correctly, DM7.2 lists wall rotations required to develop active pressure for both granular and cohesive soils. If the anticipated wall movement under active earth pressure is less than that required to develop active presures, then you should probably assume that Ko conditions apply and that the active condition will not fully develop.

The relationship between change in earth pressure coefficient (from at-rest to active) and wall movement may not necessarily be linear.

Hope this helps,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[UcfSE]

If you have access to a copy, "Principles fo Geotechnical Engineering" by Braja Das covers surcharge loads on retaining walls along with point load, line load and strip load.

 

[jdonville]

UcfSE,

Previous editions of the text (such as the 2nd Edition, which is the one I have on my shelf) leave out important subtleties in the presentation of some of the expressions, I find, such as the Boussinesq vertical stress below the corner of a rectangular foundation and Jarquio's derivations for lateral pressure due to an infinite strip surcharge.

Use with care.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[UcfSE]

Thank you for pointing that out Jeff. I'm using the 5th edition in my class this semester, and also have the 4th on my shelf. What I remember from the reading the book is the increase in stress on a retaining wall due to surcharage loads was derived using elasticity and then modified to match experimental results. Is that a reasonable approach, do you think? I don't have my books with me here at work to verify this.

 

[jdonville]

UcfSE,

There are several different approaches - some more, some less conservative.

I prefer to use elasticity-based methods, at least as a first attempt, as 1) the results tend to be more conservative than other methods and 2) many public agency design manuals specify or recommend the use of such methods.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[BigH]

UcfSE - Bowles in his fifth edition actually goes through the gist of the development of surcharge loadings on retwalls.