100+ Tiny Submarines or…

Does this photo from the South Spokane St project show more than 100 tiny soil-traversing submarines with periscopes up, or does it show earthquake preparedness?  Sci Fi authors aside, the correct answer is… preparation for an earthquake. 

Earthquake Drains Installed at 4th Ave. S and S. Spokane St.

Earthquake Drains Installed at 4th Ave. S and S. Spokane St.

So why the pipes at 4th Ave S and S Spokane St?  These earthquake drains (the periscope-looking things) relieve underground water pressure in the event of an earthquake.  The only time these “tiny submarines” see water is when the ground shakes vigorously – then they act as vents for the pressurized underground water to escape upward.  That minimizes “quick sand” formation, which as you can imagine has the potential to undermine the soil’s ability to support structures.  To keep that water from weakening the soil, these drains will guide it to a surface of rocks and soil where the water can gently settle.  It’s an important construction element for the South Spokane project since the site is, at least partially, in one of Seattle’s many liquefaction zones. Suffice to say, it’s good to know these pipes, although in the end not seen, are now under there.