Active lateral soil pressure or At - rest ? 11

[BFstr]

Hi,

I am new to this forum so my apology if I am doing in- correctly. My question is when they ask you to design a retaining wall how do you recognize that you have to apply active lateral soil pressure or at- rest? I know by definition if wall moves away from soil we should use active but in beginning I don't know if wall moves or not? Is it something that can be found in geotech report? Is it my judgment? The geotech report does not contain any information about wall since it is a new decision that we would rather build a retaining wall instead of sheet piles. I appreciate if you can direct me.

Sincerely,
BFstr

 

[rowingengineer]

BFstr,
This is an area where you will find many differing opinions, even from book to book. Generally Geotechs in my area recommend Ko as your backfill pressure because of compaction of the material behind the wall, If the wall is higher than 3m They would recommend even more due to this compaction effect. This is important when building above the retaining wall within the wedge failure, as you do not want tension cracks behind the wall. A good book for discussion on this is "foundation analysis and design by Joseph E Bowles" Ch12-10.


When in doubt, just take the next small step.

 

[hokie66]

There are a lot of threads on the site about this issue. Suggest you use the Google search at the top. Personally, I have always used active pressure for cantilever walls and at rest for basement walls, unless another model is advised by a geotechnical engineer.

 

[BigH]

and remember - at rest is always a higher earth pressure than active - depends on how safe you want to be - i.e., using something, perhaps, in between theoretical active and at-rest.

 

[fattdad]

If the wall design can tolerate 1 inch of horizontal movement for 10 ft of wall height, you can design using active earth pressure - you have to first decide whether you want the wall to move this much. If you don't then use at-rest earth pressure.

If the wall can't move as stated above (i.e., restrained at teh top), you have to use at-rest earth pressures.

I'd never just use at-rest earth pressures to account for compaction forces. I'd include a rectangular surcharge pressure to account for surface loads (which can induce additional earth pressure) and also account for compaction loads.

f-d

¡papá gordo ain’t no madre flaca!

 

[BFstr]

Thank you all for responding to the call for help.
I appreciate each of you.

BFstr.

 

[jdonville]

It can also depend on the type of wall - rigid walls will be more at-rest, flexible walls will be more active. Check to make sure that your wall will actually tolerate sufficient deflection to mobilize active earth pressures.

J

 

[BFstr]

Hi jdonville - Can you please give me few practical cases that for sure we use at-rest? And few real world examples we use for sure active pressure please.

For a gravity retaining wall that to me is a rigid solid wall then according to you at-rest is more applicable than active. Am I right?

Thanks,
BFstr.

 

[jdonville]

BFstr,

More likely than not a gravity wall will experience at-rest pressure. Basement walls are designed for at-rest pressures so they can handle the load without excessive deflections.

Sheet pile and soldier pile walls are by definition flexible and will yield. The question is how much will they yield and will it be enough to mobilize full active pressure?

For support of existing structures (what I do for a living), design for at-rest pressures, unless the existing facility can handle some significant movements (usually not the case!).

Semigravity cantilevered walls are a bit of a question mark. I would preliminary design for at-rest, especially as compaction behind the wall will induce additional earth pressure.

The compaction issue is why you will see the use of small plate compactors in close proximity to the facing panels of a MSE wall.

Jeff

 

[csd72]

BFstr,

If the wall is propped such as a basement wall with a concrete floor restraining the top then definately use at rest.

If it is an isolated wall with no deflection issues (such as appearance or adjacent structures) then I would definately use active.

Everything else in between is up to debate.