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:

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.