The 2001 earthquake that brought down a length of State Route 99 running through downtown Seattle was a measly 6.8 on the Richter scale . But rather than rebuild the Alaska Viaduct , as the bivalent - decker part was known , urban center officials instead decide to take the superhighway underground in their very own Big Dig . To do so , Seattle ’s using “ bighearted Bertha : ” the large Tunnel Boring Machine on Earth .
build for the barb by Hitachi in Osaka Japan , the $ 80,000,000 grownup Bertha measures 57 feet in diam , 325 feet in length and weigh 7,000 tons . She ’s commanded by a bunch of 25 and is design specifically for the soft dirt determine under the Emerald City .
As Bertha winds her room under Seattle and mastication through an estimated 35 feet of soil a day , her cutterhead will exercise 88,000,000 pounds of pressure on the forward wall of soil , grind down the stratum and depositing it on a conveyor belted ammunition directly behind it . Soil conditioners are contribute to the rubble , rendering it an easier - to - manage goop as it is pushed back up to the surface , 80 substructure above . To foreclose cave - ins , Bertha automatically put up pre - fab concrete panels and seals them with grout to create the burrow walls using a twain of erector arms .
Also behind the cutterhead is the trailing power train , a series of three cars curb the control elbow room as well as the crew ’s shop , power cellphone for the hydraulic wall - rear branch with the backfill grout scheme , and electrical transformer , respectively . Since most of the wearisome process is automated , the operator and a duo of applied scientist , oversee the clipping process while the other 22 crew members follow the path ahead , keep the cutterhead teeth , and start the non - automated burrow - paries erector .
The task is on track for its 2015 completion particular date . When it ’s done , the people of Seattle will not only have a fresh belowground state highway open of withstanding a 9.0 quake but also a monumental new public space along the city ’s waterfront where the old SR-99 used to stand . It ’s a profits - win . [ Car and Driver – Washington State DOT - Images : WS DoT / Flikr ]
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