Rockery wall 11 feet tall

[countyreviewer]

The backfill is 2:1 minimum may be larger. Can no surcharge be used in the calculations? Also reviewing lateral active pressure and engineer used F=0.5 We Ka H^2 (Cos g-f) g=deg. wall friction assumed 22, f=degrees anale of native soil cut slope 9.5degrees assumed
it reduces lateral force by half

 

[EngineeringEric]

Surcharges can be used in calculations... but is there a surcharge? This is kind of an open question and I am not really sure what you are looking for?

the 0.5 is to take the area of the backfill force. The force is triangular of depth H, and the leg is K*We*H...
So area is 0.5*H*H*We*K.

There is NO reduction in the force.

there are K_active, K_passive, and K_not. and Ko is the cos(g-f)... Ko is used as stricter than Ka since Ka requires movement to enable (to some degree)

 

[countyreviewer]

The back slope is 2:1 to top of wall, doesn't that have to be added into the lateral force or can it be assumed negligible? When should it be included? If Ko is used it reduces the horizontal force so when the force os sliding or overturning is used, isn't this reducing his actual force by using Ko instead of Ka? Thanks for help

 

[Archie264]

Here are some links that might help a little. I couldn't make the first one work, maybe you'll have better luck?

http://www.nbmg.unr.edu/nesc/rockerywall.pdf

http://www.clarkcountynv.gov/Depts/development_services/HowToGuides/rockery_wall.pdf

http://www.ci.brier.wa.us/Acrobat_Forms/Building/RockeryInfo.pdf

http://www.wsdot.wa.gov/publications/manuals/fulltext/M22-01/730.pdf

http://cwa.mesquitenv.gov/SiteObjec...48340F2E95FEA44/file/RockeryWallStandards.pdf

 

[EngineeringEric]

Ko is greater than Ka. It is not reducing the lateral earth pressure, It is how one designs the lateral earth pressure on the wall. I would see Archie's links for verification.

 

[EngineeringEric]

with friction angle = 22. Ka=0.45 & Ko = 0.63.... So Ko>Ka or... Force from Ko > Force using Ka

 

[ztengguy]

ideally you would figure out the area of the additional soil above the wall and figure out a new height to use. So if its 2:1 behind your 11 foot wall, your H value should be more than 11'

 

[countyreviewer]

He shows his friction angle as 34 and calculates his Ko as 0.11, I get Ka to be 0.31 with the 1-sin 34/1+sin 34

 

[RFreund]

You should use Coulomb equation to calculate your K value which around 0.3 sounds about right. Is the slope broken? There is a spreadsheet here with Coulomb equation. Do you have a snow load in this area? That is typically the minimum surcharge. However if there will be a sidewalk or traffic than this would be another source.

Also there is a FHWA Rockery Design guide I believe, Archie may have referenced it.


EIT

http://www.HowToEngineer.com

 

[BigH]

See:

http://www.cflhd.gov/programs/techD...ries/documents/01_Rockery_Entire_Document.pdf

I have another one - a good one but don't have the url noted.

 

[msquared48]

The best reference here would be a geotechnical report for the project, particularly with a sloping backfill and 11 feet of retainage. Is there one for the project?

Personally, I would expect the lateral pressure to increase at least 30% for a back slope of that magnitude. Some Geotechs use a minimum active pressure with a surcharge, others just use a higher active to mimic the slope effect. Seen it both ways.

Mike McCann
MMC Engineering

 

[FixedEarth]

That is a lot of retained height for a wall with no Geogrid, mortar or steel reinforcement. Did you check rotational stability? How about base width/wall height ratio, embedment depth, sliding F.S.,overturning F.S., seismic bearng capacity, allowable static bearing capacity, settlement, inter-rock overturning and eccentricity.? What is at the toe of this wall? This is not an easy job.

http://www.soilstructure.com/