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# three-dimensional earth pressure

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 fififififififi (Civil/Environmental) 14 Jul 12 6:07
 Hi guys, I'm Fafo from Italy. How can I consider the dimension along y axis (see figure) on the calculation of earth pressure in a gravity retaining wall?
 Ron (Structural) 14 Jul 12 7:04
 Per unit of length. For example, in imperial units, the pressure at the bottom of the fill would be in psf/ft. If metric, you might use something like kPa/m (I don't use the metric system often, so my units might not be correct with conventional practice).
 GeoPaveTraffic (Geotechnical) 14 Jul 12 7:33
 Ron is correct. However, I assumed you were interested in how to account for earthpressures acting along the y axis. Unless the ground slopes significantly in the direction of the y axis, there is no unbalanced load in that direction. Therefore there is no affect on the wall. Mike Lambert
 fififififififi (Civil/Environmental) 14 Jul 12 8:33
 Thanks for the reply. For walls with different height along the y axis, can I still apply Coulomb theory? Maybe, applying Coulomb to account for earth pressures acting along the y axis, I overestimate the thrust or I neglect any three-dimensional effect?
 GeoPaveTraffic (Geotechnical) 14 Jul 12 20:47
 Generally 3D affects are neglected. I can't think of a single time i've considered them in 24 years. Mike Lambert
 GeoPaveTraffic (Geotechnical) 14 Jul 12 21:34
 I should have said that i've never considered 3D affects on the earth pressures for retaining walls. I have considered 3D affects in many projects over the years. Mike Lambert
 Guest (Visitor) 15 Jul 12 5:56
 Thanks! I know, in a retaining wall project the 3D effect are neglected; mine was a "theoretical curiosity" . In your opinion, is it possible still apply Coulomb theory?
 fififififififi (Civil/Environmental) 15 Jul 12 6:15
 p.s. : guest = fafo
 hokie66 (Structural) 15 Jul 12 7:32
 Whatever theory you are using, pressure is the same in all directions.
 IDS (Civil/Environmental) 15 Jul 12 19:51

#### Quote (hokie66)

Whatever theory you are using, pressure is the same in all directions

??

Not in any theory modelling soil behaviour reasonably accurately.

In answer to the OP, the soil won't be close to an active state in the Y direction, so normal retaining pressure theory would not be applicable. A 3D FEA would be the best way to get a reasonably realistic picture of what is happening.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

 hokie66 (Structural) 15 Jul 12 20:48
 I don't know what made me say that. Soil is not a liquid or gas, so the pressure is not equal in all directions.
 fififififififi (Civil/Environmental) 16 Jul 12 4:18
 IDS say : "A 3D FEA would be the best way to get a reasonably realistic picture of what is happening." Correct! Using finite element code (for example Plaxis3D ?!) But do you know any analytical method to solve this problem? Do you know any issue (or publication)?
 fififififififi (Civil/Environmental) 18 Jul 12 17:02
 nobody?

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