GeoFoam - lateral pressure on walls 3

[JAE]

I'm thinking about using a geofoam product (EPS) on a ramp going up to a parking garage deck and the ramp is bounded by precast walls on either side.

The use of the EPS under the slab will help to keep vertical settlements down as I can balance the excavation and depth of foam to keep the net increase in pressure under control.

What I haven't found yet is what the lateral pressures on these walls might be if I use the geo foam product. I plan to stack the foam to produce a sort of pyramid of soil under the ramp and wedges of geofoam extending up from the base of the walls and getting wider as you go up. Trying to minimize the amount of foam to buy as it is more expensive than compacted fill.

If I produce a wedge of foam on a 1.5H to 1.0V slope would the lateral pressure on the walls be essentially zero?

 

[Ron]

JAE...no, the pressure will not be zero. The foam will transmit laterally as a diaphragm for each stacked piece; however, the compressive strain in the foam will attenuate a lot of the load...just don't know how much. Think of it this way...if you put a sheet of EPS vertically against the wall and filled soil behind it, wouldn't the wall still feel the pressure that is placed on the sheet of EPS, minus the attenuation?

If you use a lightweight fill, such as Elastizell or other cellular concrete, the lateral pressure would then be zero.

 

[BigH]

It seems JAE is planning to take the EPS outside the "active wedge" line - it seems reasonable, then, that the lateral pressure on the precast walls would be quite small - the pressure due to the "lateral" weight of the EPS (but circa 70ft of EPS = 1 ft or soil fill) and the lateral thrusts due to the traffic. I agree Elastizell or similar materials will have near zero pressure on the walls except, of course, during their plastic placement state. I would think the precast walls have some reserve against lateral pressure.

 

[JAE]

Ron, BigH basically describes what I'm looking at.

I agree if I put a vertical board of EPS on the wall the soil behind the EPS will simply transmit the pressure sideways.

But as you progressively change that "vertical rectangle" of EPS into a triangular shape with the diagonal extending from the base of the wall upwards and away from the wall it seems like the lateral pressure will diminish in some progressive pattern.

At 1.5:1 I would think my soil beyond the wall is essentially a stable pile of dirt (think pyramid) and there'd be only lateral force from the ...ahem...technical term coming....squishyness of the EPS (poisson's ratio activity).

I will probably have to contact someone who makes this stuff and see if there is data on this but thought I'd cast it out here in ET land to see what others know.

 

[GeofoamSpecialist]

JAE - anytime you stack geofoam up above the angle of repose creating a vertical facia wall with the geofoam - you end up creating a zero lateral load on the vertical facia wall.

If you need more information - please do not hesitte to touch base with me at geofoam@insulfoam.com

Nico Sutmoller
Geofoam Specialist
geofoam@insulfoam.com

http://www.insulfoam.com

 

[msquared48]

JAE:

What about the surcharge load from the traffic? Seems to me that force will still transmit to the wall regardless of the presence of the foam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[DAVIDGF]

JAE's thoughts about an upside down pyramid of blocks to replace the sliding soil wedge are right on track. EPS Geofoam exhibits 2 important physical properties that will result in a zero lateral load by employing the proposed layout of the large block fill. The Poisson's ratio for EPS Geofoam is 0.05 which virtually precludes any lateral load transfer from live traffic loads. It also has an above average co efficient of friction (conservatively 0.6). As long as the native soil is sloped lower than the internal friction angle of the native soil, thus outside of the active wedge, it is physically impossible to develop enough lateral earth pressure to move the blocks between the layers. In fact, to lower costs and based on the zero lateral load scenario, many designers are simply employing a shotcrete finish on the vertical face of the blocks instead of cast in place or precast concrete panels. Link to a great article written by the design engineer that illustrates JAE's project on a little larger scale....

http://www.rebuildingamericasinfras..._aids_in_bridge_replacement_project-8228.html

 

[JAE]

Nico - from what I've seen in numerous publications the lateral load is essentially zero but it seems to me that there's be "some" lateral force that would develop simply via poisson's ratio. I feel like I need to design to some nominal level of load from the foam if it is set directly adjacent to a covering precast panel (set foam, set panel, infill with pea gravel between for instance).

I'm not sure I'd want to use shotcrete on the foam per the article you linked to DAVIDGF.

 

[GeofoamSpecialist]

JAE - If you are going to use a precast panel wall as the facia wall, which is generally placed on a footer and then tied into the load distribution slab (LDS). With precast panel walls, we generally have a gap of several inches between the precast panel wall and the geofoam assembly.

DAVIDGF is absolutely correct in his statement and fully concur about the use of a shotcrete finish on the vertical face of the blocks instead of cast in place or precast concrete panels to further reduce costs on any project.

Nico Sutmoller
Geofoam Specialist
geofoam@insulfoam.com

http://www.insulfoam.com

 

[JAE]

Nico -
I can't use shotcrete as we are abutting a precast structure and have to match it.

With a separate PC wall - you refer to a load distribution slab. Does this have to be a separate slab below the upper fill & pavement or can the upper pavement serve for both? In other words, I'd have a thick pavement above, granular base, then granular or select fill, perhaps a poly barrier on top of the EPS, then the EPS. Any thoughts?

 

[GeofoamSpecialist]

JAE - If I had to match an abutting structure, I would still go with a shotcrete facing as that can be sculpted and colored to match any desired situation (

http://www.boulderscapes.com)

Generally when a LDS is used we place the granular base over the LDS and then your final pavement - when using a LDS you probably will not need a poly barrier. Just wondering as to where the project is located and is this a commercial or DOT project as that may or may not have an influence.

Nico Sutmoller
Geofoam Specialist
geofoam@insulfoam.com

http://www.insulfoam.com

 

[JAE]

Non-DOT. This would be a private parking garage - specifically a ramp up to a garage upper deck. Would have road salts in the winter.

 

[Ron]

JAE...thanks for the clarification...what I was addressing was that "squishiness" and the friction between the layers. Pin the layers with pegs or adhesive and I agree.

 

[DAVIDGF]

JAE- We have a sample section detail available that shows how to tie in a precast concrete panel into a concrete load distribution or pavement slab. The detail shows a LDS poured on the foam with a separate granular layer and pavement course. You can also tie the pavement course directly into your fascia wall. It is a function of the weight of the traffic loads. Heavy highway embankments utilize thicker pavement courses and sub grades on top of an LDS and the Geofoam to distribute the live loads over a larger area and thus reduce the density requirement and cost of the EPS. If you have lighter vehicle/pedestrian traffic for your ramp project, a thinner pavement section may be justified which could preclude the use of a separate LDS.

http://www.insulfoam.com