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This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com


Tuesday, June 19, 2018

What in the world is "geofoam?"

In the past week, I have traveled the 135 mile route between Seattle and Vancouver, B.C. twice, each trip taking more than 6 hours when going north.  A significant part of the problem is waiting at immigration at the border, but an equally significant problem is the crazy highway maze from the border into Vancouver: continuous spots of merging 3,4,5,6 lanes down to 1,2 or 3.  Amidst the frustration, my suppressed desire to become a highway engineer emerged: either to design the interchanges properly using fluid mechanics principals, or to design them to punish the many drivers who skirt to the right-hand side "truck only" or "exit for duty-free" places to cheat and move way up in line.
     With this recent thinking about traffic engineering, I was interested today in an article on the WSDOT blog site regarding "geofoam" which I had never heard of. It is used in place of dirt because the use of real dirt takes longer and has higher costs. Dirt has to settle, and crews have to wait until the ground has settled before building a structure on top of it. The use of geofoam also reduces the weight on underlying soils: blocks of geofoam are placed on a section of ground that is greater than the weight of the geofoam. The blocks are glued together with a quick-setting roofing adhesive and then secured to the ramp walls with reinforcing steel. Ready now for concrete to be poured on top!
     So, what is geofoam? Does it have anything to do with "geo"? Not as far as I can tell, though it's probably more stable than the "ghost poop" foam beads that are used to cushion materials in packaging! It is "expanded polystyrene" manufactured into large lightweight blocks. I couldn't find a list of the elements/compounds in it, but according to one site, it is a "closed-cell, strong, but lightweight premium quality expanded polystyrene (EPS) foam." It is used in a variety of "residential, commercial, and industrial applications." Polystyrene has the general chemical formula (C8H8)n with a density of  1%-2% of that of soil of equal strength. 
     Geofoam is used because, for engineers, it has predictable properties compared to soil fills. It is basically (but not completely, see below) inert so that it won't spread into surrounding soils, e.g., lawns, gardens, farmlands...  It can even be installed by hand and does not require heavy machinery for installation.  It's quick and easy to install and can be installed in any type of weather and night or day, i.e., cheaper installation costs.  It can be dug up and reused.
     On the other hand, there are some serious disadvantages: It is a fire hazard if untreated.  It is soluble in petroleum solvents, eek.....if it comes into contact with a 'petroleum solvent' it turns into a "glue-type substance unable to support any load." Engineers have to figure out buoyancy problems because of it's low density: cars were crushed against a ceiling in one instance after floodwaters below a carpark floated it.  It is susceptible to insect infestations when used in buildings.
    Conclusion: The "geo" in geofoam has nothing to geology!


1 comment:

PDalton said...

Given its' lower density, are there prospects to use geofoam below foundation grades in areas susceptible to soil liquefaction? Would these blocks, with appropriate containment and available buoyancy, provide both support for the structure above, and potentially isolation from seismic impacts? It sounds like there may be some potential for mitigating the effects of earthquakes, especially in areas where liquefaction can reasonably be expected to occur.