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.