Earth pressue where cantilever wall is restrained in vert. direction 1

[kcall2]

Is it appropriate to provide lateral earth pressure recommendations for design of a cantilever retaining wall that includes both active and at-rest values? For example, at locations where a wall turns, say 90 degrees, it is essentially restrained against rotation and therefore the strength of the soil backfill theoretically has not fully mobilized. Would you recommend that at those locations, and up to some distance away, the wall be designed to resist at-rest pressures? Is there any publications or journal articles that discuss this? Thanks for any input!

 

[ishvaaag]

Since this is in accord with established sound practice you may give that recommendation or even one more generic referring to in which circumnstances active earth push can be used. Anyway, a competent designer should know.

 

[fattdad]

I'm thinking this may be a moot point. Rankine active earth pressures and correlations to the coefficient of at-rest earth pressures are based on plane-strain conditions. By definition, you don't have plane strain conditions at a corner, so that's the first issue to consider. Because it's not plane strain conditons, the stress would be less at the bend.

I'll discuss this with our strucrtural engineer, but it's likely the greater concern would be where a foundation wall "t's" into a basement wall. Not sure about this. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[wedlmic]

"Stability of a retaining wall is properly based on the active earth pressure" - Peck, Hanson & Thornburn, Foundation Engineering, Page 424. To fail, it must move, if it moves it developes active state. However, I have seen in some text where the use of At-Rest pressures is recommended for "permenant" retaining wall designs verses those used in a temporary nature. I have not seen a wall yet where there was a change in the assumed lateral earth pressure theory at interior corners - good question, I'll be up all night.

Wedlmic

 

[InDepth]

Well...out of curiosity, couldn't the soil arch around the corner?

 

[fattdad]

Well...out of curiosity, couldn't the soil arch around the corner? [\quote]

Is this in referenced to my earlier comment? If so, I don't get the connection.

Regarding movement at the top (i.e., for the cantilever design), I know designers that use at-rest forces for cantilever walls as they don't want the wall to move, even though it could. Bear in mind, if you design for active pressures, you are anticipating an outward movement of 1 inch for a wall height of 10 ft. If you design a cantilever wall using at-rest wall pressures, you are thereby designing a wall that can restrain the at-rest forces and will not move this amount. You'd also not have to worry about your original concern.

f-d

¡papá gordo ain’t no madre flaca!

 

[dgillette]

See J.M. Duncan, G.W. Williams, A.L. Sehn, and R.B. Seed in December 1991 ASCE JGE "Estimation [of] Earth Pressures Due to Compaction." (Errata March 1992, discussion by Ralph Peck and closure July 1993) It shows that, with a stiff wall, fill compacted tightly against it can produce pressures significantly higher than Ko condition.

The bend in the wall would probably create a local stiffer area, even if the main part of the wall. As fattdad says, this is not a place where the plane-strain assumption is truly applicable and the analysis would be tougher. Unless the wall is quite large, justifying detailed analysis, my inclination would be to put in a few extra bars and make sure the compaction doesn't get overdone next to the wall.* (Don't run a Cat 815 right next to it.)


*There are cases where there MUST be very tight compaction against the wall, such as dam spillways. This usually means stout gravity walls or counterforted walls that won't deflect appreciably.