Michigan P.E. makes a good catch RE: sg

To the editor:

Great issue (February/March 2013), read it from cover to cover.

One thing I noticed though, on page 40 it states: “..were made of polypropylene, which has a specific gravity greater than 1,…” is incorrect. Typically polypropylene has a sg of 0.905 and that is why it floats, not sinks, as alluded to in the article. 

Have a good one and, again, great issue!

Russ Sutton, P.E.
Civil Engineer–Water, Wastewater & Utilities
U.S. Forest Service–Region 9 Technical Services Team
Cadillac, Mich.

Reply

Correct sentence from February/March Geosynthetics:

Because the geotextiles that were used in this project were made of polypropylene, which has a specific gravity less than 1, UESI had to find a solution that would allow erosion control protection under the waterline while ensuring that the products would stay in position during the service life of the project.

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