NPI's Cascadia Advocate

Offering commentary and analysis from Washington, Oregon, and Idaho, The Cascadia Advocate is the Northwest Progressive Institute's uplifting perspective on world, national, and local politics.

Friday, July 20th, 2018

Excavation of East Link’s downtown Bellevue tunnel is done, five months ahead of schedule

Today, Sound Tran­sit invit­ed rep­re­sen­ta­tives from the mass media, its con­trac­tors, and its inter­a­gency part­ners at the state, local, and fed­er­al lev­el to down­town Belle­vue to com­mem­o­rate a lit­er­al break­through: the com­ple­tion of the min­ing of the tun­nel that will car­ry trains under­neath the city’s main busi­ness district.

Com­plet­ed five months ahead of sched­ule, the new tun­nel is approx­i­mate­ly one third of a mile long (1,985 lin­ear feet, to be spe­cif­ic). It is twen­ty-sev­en feet and ten inch­es tall, and thir­ty-four feet wide. Exca­va­tion began a year and a half ago, around the time NPI’s Per­ma­nent Defense cel­e­brat­ed its fif­teenth anniversary.

“This tun­nel is the cul­mi­na­tion of over a decade of vision, hard work and tenac­i­ty by local and region­al lead­ers, plan­ners, work­ers and many, many mem­bers of the pub­lic who all insist­ed on a great tran­sit con­nec­tion through down­town Bellevue.”

“East Link — and this tun­nel — will con­nect our com­mu­ni­ties, sup­port our econ­o­my and pro­vide a fast and reli­able way to get out of traf­fic for peo­ple all over the region,” said Sound Tran­sit Board­mem­ber Clau­dia Bal­duc­ci, who joined CEO Peter Rogoff and Belle­vue offi­cials for a cel­e­bra­to­ry speak­ing pro­gram at the site.

After the con­clu­sion of the speak­ing pro­gram, the media was invit­ed to join Sound Tran­sit staff mem­bers for a tun­nel walk-through, begin­ning from the south por­tal and end­ing at the new­ly-cre­at­ed north por­tal (where crews are still working).

It took about ten min­utes of walk­ing at an unhur­ried pace to tra­verse the length of the tun­nel. Once we reached the oth­er end, Atkin­son Con­struc­tion work­ers demon­strat­ed the equip­ment they’ve been using to dig the tunnel.

Unlike the tun­nels dug by WSDOT’s Bertha, and by Sound Tran­sit’s small­er TBMs (the Emer­ald Mole, Bren­da, and Pamela), this tun­nel was dug using the sequen­tial exca­va­tion method, also known as the New Aus­tri­an tun­nelling method.

Sequen­tial exca­va­tion involves sev­er­al steps that are being con­stant­ly repeat­ed: soil removal, the spray­ing of pres­sur­ized con­crete known as shot­crete for sta­bi­liza­tion, and the instal­la­tion of lat­tice gird­ers for addi­tion­al support.

Unlike with a tun­nel bor­ing machine, there isn’t a giant cut­ter­head and a trail­ing appa­ra­tus that has the length of a foot­ball field. When I vis­it­ed the con­struc­tion site last year, we were able to walk right up to the spot where the dig­ging was going on and watch soil being loaded into dump trucks for removal.

Accord­ing to Sound Tran­sit and Atkin­son Con­struc­tion, 72,000 cubic yards of soil had to be removed to dig the tun­nel, 9,000 cubic yards of shot­crete were applied to sta­bi­lize it. And 479 lat­tice gird­ers were put in for addi­tion­al stabilization.

The tun­nel is twelve feet from the sur­face at its shal­low­est point, and thir­ty feet from the sur­face at its deep­est. It cross­es under Main Street and then fol­lows 110th Avenue NE, cross­ing NE 2nd Street and NE 4th Street. It then ends at the site of the future Belle­vue Down­town Sta­tion, which abuts City Hall.

Here’s an excel­lent map of the align­ment, cour­tesy of Sound Transit:

Sound Transit's Downtown Bellevue East Link alignment

The East Link align­ment in down­town Belle­vue (Graph­ic: Sound Transit)

The City of Belle­vue pro­vid­ed $100 mil­lion worth of in-kind con­tri­bu­tions to help Sound Tran­sit deliv­er the tun­nel. These includ­ed prop­er­ty and util­i­ty relo­ca­tions. The con­tri­bu­tions were for­mal­ized in a 2015 Mem­o­ran­dum of Under­stand­ing approved by the Sound Tran­sit Board and the Belle­vue City Council.

The choice of a sequen­tial­ly exca­vat­ed tun­nel allowed Sound Tran­sit to avoid tear­ing up 110th Avenue NE for an at grade align­ment or a cut and cov­er tunnel.

The end result is a light rail align­ment that goes where the peo­ple are (instead of an align­ment crammed into the I‑405 right of way) that did not involve shut­ting down a major artery in down­town Belle­vue to construct.

The entire East Link project includes ten sta­tions linked by four­teen miles of track. Con­struc­tion is sched­uled to be com­plete in time for a 2023 grand open­ing. When oper­a­tional, it will be pos­si­ble to go between the Microsoft cam­pus and down­town Belle­vue in just ten min­utes, south Belle­vue and Sea-Tac Air­port in just fifty min­utes, or Mer­cer Island and the Uni­ver­si­ty of Wash­ing­ton in just twen­ty minutes.

NPI con­grat­u­lates Sound Tran­sit on today’s big mile­stone. It is won­der­ful to see progress being made on mak­ing East Link a real­i­ty all around the Eastside.

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