Embedded Walls - Passive Increase for Close Spacing

[RFreund]

Can you / would you / should you increase the passive pressure to account for the "surcharge" soil load when you have embedded walls which are facing eachother with a close spacing (i.e. 2 cantilever walls bracing opposite sides of an excavation)?

See here:

https://dl.dropboxusercontent.com/u...Retention/Embedded walls Passive Pressure.pdf

EIT

http://www.HowToEngineer.com

 

[FixedEarth]

The "surcharge" should not be looked at providing additional passive resistance since it may be removed in the future. The surcharge influence line & the passive failure plane should not overlap. See attached comments.

Also look at DM 7.02 manual for checks on piping, basal heave and rotational failure.

http://www.soilstructure.com/

 

[RFreund]

FE - thanks for the comments and I should have said "assuming that piping, basal heave and rotational failure checks are all "OK"".

I was think of a situation where this is temporary shoring and either a case where there are no braces or before braces are installed and you have 2 cantilevered walls. Lets also assume that the soil on one side is not going to be removed (maybe its a case where the shoring will be left in place. It seems that the closer the walls are together, the greater the contribution of the soil being retained on the opposite side will have. I mean it seems that there has to be some benefit to this soil as it would add weight to the passive soil wedge (assuming that it is on top of the passive soil wedge). However maybe there is no good way to quantify it.

Thanks again.

EIT

http://www.HowToEngineer.com

 

[dcarr82775]

I think you could count on it, but you are 'double' loading the passive soil at the base. I have never had the situation so have not given it a lot of thought, but it seems like once you start overlapping passive from different directions you should reduce your values in some way. For lack of a better term I envision a potential to 'buckle' the soil.

 

[RFreund]

Yeah I would agree that doubling the loading could be trouble some. As for the buckling, that's where I was thinking the piping and basal heave checks would come into play.



EIT

http://www.HowToEngineer.com

 

[PEinc]

Design two separate sheeting walls, unless thare are identical loading conditions. Don't count on extra passive resistance. If there is an unbalanced hydrostatic pressure, check for boiling. Check for heave if you have soft soil.

http://www.PeirceEngineering.com