The article indicates that the walls were necessary to allow for the construction of an additional runway to meet federal guidelines requiring separation of runways during bad weather. Previously Sea-Tac had to operate only one runway during bad weather (about 40% of the time!) causing delays etc. Over 16 million cubic-yards of fill were needed for the project, and the walls became necessary as environmental mitigation for neighboring wetlands and a creek as the footprint for 2H:1V embankments would have covered wetland area. The overall project cost is more than $1.1 Billion!
Image copyright Hart Crowser
There are 4 tiers to the west wall, and the average wall-height is 74-ft with a total wall length of over 1,400-ft. The Reinforced Earth Company (RECo) was the designer and supplier of 5-ft by 5-ft cruciform shaped panels (Reinforced EarthÂ® system) with galvanized steel straps as reinforcement. One interesting thing I didn’t know about the project was that for that West wall, they had poor subgrade soils, possibly because of the neighboring wetlands. They had to overexcavate and replace 20-ft of material (mostly peat)! Our local contractors grumble about 5-ft of overex and recompact. To do the excavation they needed sheet pile shoring. (Photo by Sea-Tac Airport)
Other MSE Wall projects discussed in the article include a Tensar Mesa Retaining Wall System used at a new interchange for Interstate 24 at Manson Pike in Murfreesboro Tennessee (completed in 2004), and a couple residential retaining walls in Roseville California and Atlanta Georgia.
Thanks to Geosynthetica.net for finding the article.
A wall is an erosion control Best Management Practice
Randy commented that he didn’t understand why a wall would be in a magazine on erosion control. A wall is an erosion control Best Management Practice (BMP). Just like erosion control blankets, walls control erosion although different they are both tools in the toolbox of erosion control and sediment control professionals. For more info check out the IECA web site at http://www.ieca.org.
Sunshine Supplies, Inc.
Birmingham, AL http://www.sunshinesupplies.com
Thanks for the comment Skip. I am certainly no erosion control expert, just a lowly geotech. But what I meant was that the walls that the author chose to discuss in her article didn’t seem to be related to erosion control. I’m not complaining, I enjoyed the article. I can see walls having their place as BMPs though. If you or anyone else come across an article about retaining walls used for erosion control, let us know. –Randy
Which is the tallest Reinforced earth wall in the world?
I posed this question through my boss to some very knowledgeable folks in the MSE wall industry (on the design side). They indicated that the tallest MSE wall in the world is located in Mongolia where there were actually two built, one to a height of 51-meters (167-ft) and one to 53-meters (174-ft). But apparently one of them failed. Loess was either used as the backfill material or formed part of the subgrade and the failure was apparently somehow related to this. The wall system was one not commonly seen in the US, consisting of plastic strips with longitudinal wires running inside them. A quick google search turned up nothing on these walls. If anyone finds the info, please let us know.
Loess is beautifully capable of at one time draining water to the base, in this case the wall, causing much subsurface slip plane, and sometimes fines, or causing mass erosion in heavy storms as the percolation is moderate during accumulated wash events down gully and depression … an RE style wall would be a bit of a nightmare … did not know they had started to use plastic and wire too; bit out of touch with modern RE design as it tends to fall into storage, spoil, technical engineering and collapsed roads at Avonmouth and Midlands (Monk) so it became an unpopular subject for the English (nothing like a solid lump of concrete dug out of the Mendips and processed with old tyres in south Gloucestershire until buildings fall down … how “environmental” is that compared to an effort to utilize local forms, soils and natural fills). Too French probably or perhaps too Canadian ?! where it is used on the coast highway. Mike non-explosive tunnel cut seems also a bit of a no no
Thanks Mr. Randy Post.
I would like to know landmarking geosynthetic structures around the world.
i have work the reco for some time what is the longes wall they have bilt