Strip Foundation Loading on Catilever Wall Coulomb

[Engineer89]

Hi all,

New here and am wondering if someone can help me.

I am doing a comparison between Rankine and Coulomb theory for a retaining wall. I used a strip foundation a distance from the edge of the wall. I was able to do the analysis for Rankine but am having problems modelling the stress distribution of the foundation on Coulomb analysis.

Can anyone point me in the right direction?

Regards and thanks

John

 

[fattdad]

use the boussinesq equations and double the answer for horizontal stress. He has line load equations and point load equations so you can use what you want to when you model the stress from the strip footing.

Well use that AND the earth pressure too.

f-d

¡papá gordo ain’t no madre flaca!

 

[FixedEarth]

Here are those equations.

 

[Engineer89]

Hi all,

Many thanks for your help!

It is much appreciated. I actually used what you uploaded FixedEarth, found it before you uploaded!

Great help

John

 

[FixedEarth]

Anytime. Attached is an example calculation.

 

[Engineer89]

Thanks FixedEarth, that gives me confidence in what I have done.

I have one problem, in that I cant seem to integrate this into coulombs theory. Im trying to do a comparison between coulomb and rankine, showing how coulomb will give a slightly higher load, in that it takes into account wall friction.

For these lateral forces, do I compute them like Rankines, i.e. the area of the force and multiply by where it acts.

Coulomb theory then gives me the wedge resultant and I also work out where it acts. then Balance the passive and active to find the maximum force on the strip load.

Does this make sense?! Sorry I have done the Rankine aspect, it integrated with the surcharges easier, I just cant get the coulomb to work!

John

 

[FixedEarth]

The equations are Boussinesq with modifications to match experimental results. You can get the resultant as you mentioned by computing the area under the curve. You can then find your centroids and your thrust resultant location. The earth pressure due to backfill can be done by either Rankine or Coulomb and then you just add the backfill, any water and strip load to get your total horizontal stress. If you use a spreadsheet, say 0.5 ft depth increment, you can have one column for Rankine, another for Coulomb, another for surcharges (line, strip, point, and uniform) and then just add them up. I am sure there is a more elegant way to do it, but this works for me.

 

[Engineer89]

Thanks for the help.

Rankine was straighforward enough as you get a horizontal thrust. you then compute the areas and work out the lever. However coulomb gives me the area (i think) from its equation. So is it possible to just summate them? i.e. youre not really taking the combined effect into account

Sorry, but I cant for the life of me get this to give me a reasonable answer. Id expect it to give me a slightly higher answer than rankine, as it takes the wall friction into account, but im getting considerably lower, which does not make sense!

Thanks!

J