Modular block wall face for geofoam fill

[cphi]

I need geofoam internal friction and geogrid - geofoam coefficient of interaction values to evaluate geogrid pullout from between geofoam blocks. Anyone willing to share a similar design experience?
I may be asked to design a modular block retaining wall as a facing for a geofoam fill. The geofoam fill will support a roadway. I have designed many geogrid reinforced modular block walls, but none to "retain" geofoam. I know that geofoam will not exert a substantial lateral pressure, but I feel that I need to treat the geofoam as a "soil" in the wall design, and tie the modular block facing to the geofoam. So I need to use geofoam internal friction values and geogrid - geofoam coefficient of interaction values. To explain the design situation, the following is a simplification. The roadway alignment and geofoam fill are adjacent to the northern edge of a parking lot. The roadway grade increases in elevation from the parking lot elevation at the west end to 15 or so feet above the parking lot at the east end. The modular block wall will serve as a near vertical facing for the grade differential between the roadway geofoam fill and the parking lot.

Thanks in advance

 

[Focht3]

What do you expect will induce the loads on the modular block wall?



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[BigH]

I once did a search on rediff.com on Sytrofoam. Got a lot of good "hits" on geofoam although you also get a lot of "garbage cups", too. Still, as I remember, there were a number of papers/discussions about using geogrids between the blocks of foam. If I remember tomorrow I will look up foryou.

 

[cphi]

I appreciate the replies. I'll check out the geofoam websites, and contact manufacturers.

Focht3: Lawyers, unit fill / drainage aggregate, lawyers, geotechnical engineering judgement in treating the geofoam as a soil, and lawyers. I agree with questioning what the lateral loads source is, since geofoam is used for ZEP applications. The reason for my post here is to gain knowledge on what experience others have had with this situation, and use the knowledge and geotechnical judgement to solve the problem. Then if I have the opportunity, observe the construction and revise the design if needed. Geogrid is cheap.

BigH: Please do. Also, I'll check out the rediff.com website, although I am not familiar with it.

 

[Focht3]

It's amazing how much wall pressure those pesky lawyers exert!


How will the geofoam be placed: blocks, "sheets", or "cast in place"? I'd guess blocks; what are the block dimensions? Dimensions of the area to be filled?

One alternative would be to tie the geofoam together as a mass, allowing the wall to be placed offset from the geofoam fill. The conventional wall then becomes a protective face that doesn't carry any load - this has been done with geotextile layers and sand backfill. The geotextile is wrapped around the "face" of the fill, and geotextile is placed in fairly thin lifts.



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[BigH]

Agree with Focht3 in that geofoam shouldn't put any "earth pressure" on the fronting panels. Panels are there for decoration and protection of foam. Grids needed to keep panels in place. I wanted to use geofoam here in India but was "afraid" to try it as wick drains was virgin territory! I computed 60m of geofoam = 1m of soil, approximately (depending on what kind of soil). Pretty impressive, eh? Elastizel is only about 4 or 5:1.

 

[BigH]

I just (1Sept03 0230 India Time) checked out rediff.com and did a search "geofoam embankments retaining walls". Got something like 80 hits and many were quite good. Apparently Syracuse University and Manhattan University (Prof. Horvath) have set up "Institutes" with a view to promoting geofoam structures. Try for instance the following:

http://www.geosyscorp.com/FAQ_Master2.html

http://www.acfenvironmental.com

http://www.engineering.manhattan.edu/civil/CGT/T2olrcelif&3.html

http://www.geofoam.syr.edu/GRC_back.asp

http://www.geofoam.syr.edu/GRC_i15.asp

I think these have been typed right although I am having a hard time reading the last bit of the engineering.manhattan site.

Hope that these help.

 

[MSEMan]

I was involved in a geofoam block embankment project on a highway in Norway a number of years ago. The geofoam is more usefully thought of as a weak fissured rock rather than a soil since the material relies almost entirely on cohesion for its strength. I would tend to assume zero as the interface friction and look at the passive resistance gained from the transverse members in the geogrid structure.

One problem you may find is dealing with the steel/ aluminium/ concrete parapet at the top of the wall. An independent support structure is relatively expensive.

Given all of the above, and I know it seems decidely un-modern, but have you thought about facing the geofoam embankment with a CIP wall? In all likelyhood the critical design case would be crash barrier impact loading, but of course the overall capacity of the structure provides a certain comfort level generally. Is the soil strong enough to support a CIP wall (even one backfilled with geofoam)?

 

[cskelsey]

Dov Leshchinsky--University of Delaware--might be a good source for these design issues. He writes frequently about earth retention and wall design involving various materials. If I'm not mistaken, he also has designed software to assist calculations and material configurations.

http://www.ce.udel.edu/directories/profiles/leshchinsky.html

CPHI: Thanks for starting this thread. Keep us posted on how your project progresses!

All best,
-cK



Christopher Kelsey, editor
GFR magazine
gfr@ifai.com

http://www.gmanow.com

 

[dirthead]

I think MSESman is on the right track when he suggests getting away from internal reinforcements. I am aware of a wall that Utah DOT used on one of their geofoam embankments that was a "tilt-up" precast wall. It was basically a full height panel connected at the top to the crash barrier/moment slab. I also know that New York DOT did a job where they used a precast 'T-Wall' system and fit the geofoam blocks in between the stems. I myself once used geofoam to backfill part of a conventional soldier pile and lagging wall.

You say you "feel the need to treat the geofoam as a soil". WHY?? If you were designing a steel structure you wouldn't treat it as wood! (I'm picking on you a bit cphi because this sentiment has been echoed by many engineers.) Remember, we're dealing with a material that stands vertically, has virtually no weight, and has a poisson's ratio of zero. No load is no load! BigH got it right when he said the wall is really just protection and decoration.

Although...
There is a caveat to this that nobody has mentioned. You can have soil pressure transferred THROUGH the blocks to the wall if the entire embankment is not foam or if you don't lay-back the back of your fill section to a "stable slope". (This would be easier to describe with a picture but I think you get the idea.)