18 COVER STORY Tunnel Achievement Award ince it was established in 1996, Sound Transit – the regional trans- portation agency for the Seattle and Central Puget Sound area – has S been steadily meeting the demands of residents in need of com- muting options. With Seattle routinely ranked among the most congested cities in the United States, residents are welcoming new mass transit options with open arms. Seattle has seen steady growth in transit ridership, and residents approved additional funding in 2016 to provide further build out of the network. A large part of the mass transit solution is an expanding Link light rail network, which currently includes a connection two miles south of SeaTac Airport to downtown and northward to the University of Wash- ington. Recently, Sound Transit completed tunneling on a further exten- te Link Extension – that is scheduled for rev- enue service in 2021. Due to successful completion of tunneling in difficult ground and in a dense urban envir te Link project has been named the 2018 Tunnel Achievement Award winner. The Tunnel Achievement Award is presented by the organizers of the Breakthroughs in Tunneling TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 TUNNELINGONLINE.COM COVER STORY 19 RELATED WORK - East Link Extension The $3.7 billion East Link Extension is a 14-mile, 10-station extension from the International District/Chinatown station south of downtown to Red- mond. The segment is mostly above ground, except for a short tunnel be- low downtown Bellevue. Guy F. Atkinson Construction was awarded a $121.4 million contract to build the 1,985-lf, 34-ft ID ovaloid, 12- to 48-ft de oject includes one maintenance shaft 17-ft diameter by 50-ft deep located near the midpoint of the tunnel, a connect- ing adit to enlarged tunnel section for – Northgate Link Extension permanent ventilation fans, and 250 lf of cut-and-cover structure. Crews are excavating soft ground consisting of glacial till and outwash Short Course in conjunction with . gravel, using the sequential excava- te Link Extension comprises 4.3 miles of twin- tion metho top track railway from the existing University of Washington Station to a heading (three headings) as well as new elevated station a e te Station). Two new single side drift (6 headings). underground stations will be constructed a eet (U District TP was issued Feb. 8, 2016, with Sta eet (Roosevelt Station). substantial completion projected by te Link Extension includes 3.5 miles of 18-ft,10-in. diam- y, the job was eter twin-tube tunnel betwe eaf P eet over 80% complete. and the University of Washington Station. A $440 million contr Crews are utilizing two Liebherr 125) was awarded to (Jay Dee/Coluc JV). It is the same JV 950 to excavate the tunnel, and that completed contract U-230 for the University Link program that con- Spraymec 8100 shotcrete ro- nects downtown Seattle to the University of Washington Station, which bot to place the shotcrete lining. opened for service in 2016. The tunnel design team included Sinc te Link began in 2014, the two tunnel obs Engineering boring machines, weighing 600 tons each, excavated more than 500,000 Gr TB. Construction is ex- cubic yards of soil and installed 7,352 concrete tunnel liner rings. pected be completed by spring 2020. F ed a Hitachi Zos ed Revenue service for East Link Exten- on the U-230 project, in addition to a refurbished Robbins EPB, which had sion is anticipated for 2023. TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 20 COVER STORY been previously used on a project in quired innovation from the design Singapore. Tunneling was completed side. “The tunnels under the Univer- Sept. 1, 2016, with the second hole- sity of Washington campus provided a through at the University of Washing- series of design and construction chal- ton Station. lenges,” said Gregg Davidson of - In addition to the main running len Jacobs Associates, Sound Transit’s ontract included con- design consultant. “These ranged from struction of 23 cross passages between analysis, design and testing of a float- Seattle Voters tunnels that will serve as emergency ing track slab in the tunnel under the evacuation routes and will contain noise and vibration sensitive campus Approve ST3 controls for electrical and mechanical buildings, to schedule constraints on systems. Remaining work under sepa- how long the could actually . 8, 2016, voters approved rate contracts includes installation of work within the campus boundaries.” Sound Transit 3 (ST3), a ballot measure track beds, rails and communications Basically, the floating slab comprises that provides $54 billion in funding to systems, and fit out of the stations. precast concrete structures that sit on expand and improve transportation in natural rubber pads, resulting in a sort the Seattle area. ST3 will add 62 miles Urban Tunneling of shock absorber. Sound Transit had of light rail, completing a 116-mile re- About 3,800 ft of the tunnel align- tested a 400-ft prototype floating slab gional system. ment traverses under the Univer- in the University Link tunnels. “Our region has embraced a genera- sity of Washington, which created To the north, the alignment crosses tional opportunity to move forward a unique set of challenges for tunnel a densely populated and growing with a transit network to connect construction. The school is renowned residential area, so the decision was millions of people across three coun- as a leading research institution, and made to keep the tracks underground. ties,” said Sound Transit Board Chair had strict limitations for noise and “Tunneling was the best option in that and King County Executive Dow Con- vibration – during construction and area due to minimizing construction stantine. “After decades of waiting, we operation – to ensure that its facili- impacts on residents as well as mini- are ready to start building a light rail ties were not impacted. To further mizing property acquisition in such a system that will grow our economy, reduce impacts on the university, an densely packed area,” said Kimberly improve our quality of life, and ensure agreement was reached to limit the Reason, Senior Public Information Of- access to jobs, education and all the construction duration for tunneling ficer for Sound Transit. Central Puget Sound has to offer.” under campus. Like many projects in the Seattle By 2021, Sound Transit will com- “We had 304 days to build the area, the ground conditions posed plete light rail to Roosev - tunnels fr challenges. Typical reaches f - gate Link and in 2023 trains will reach crossed under campus,” said Rick Cap- gate Link include glacial soils compris- cer Island, Bellevue, Overlake, ka, Deputy Project Director – - ing sands, silts, gravels, clays and scat- Shor e Terrace and gate Link. “That entailed completing tered boulders under the water table. Lynnwood. From there, Sound Tran- two tunneling passes as well as ex- In addition, crews had to navigate a sit will keep building until the agency tracting, refurbishing and relaunching section of hard glacial till. To tackle has completed a 116-mile regional sys- y that we the ground conditions, earth pressure up will be getting light rail were able to meet that milestone with balanc e selected. Un- to Federal Way, downtown Redmond, room to spare.” like the U-Link project, Sound Transit Tacoma, West Seattle, Ballard, Everett, Tunneling under campus also re- allowed the use of refurbished ma- South Kirkland and Issaquah. TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 TUNNELINGONLINE.COM 22 COVER STORY chines, in part due to the availability Closed Book of used machines in that size range. te Link Extension is In addition to the mainline tunnels, approximately 65% complete and is on cross passages were needed every 800 track to open in 2021. Tunneling was ft. The cross passages, which ranged completed in 2016 and all construc- from about 15 to 25 ft in length, were ontract has been built using the sequential excava- completed, moving Sound Transit one tion metho vancing in 3-ft step closer to providing better service rounds and supported with shotcrete to residents. and lattice girders. “Even though the “The highlight of the project has cross passages were short in length, been the successful collaboration, excavating for them was very com- once again, between Sound Transit, plex due to the ground condition,” the final design team, the tunnel con- Capka said. tractor and the construction man- agement folks, which has resulted in Ground Freezing te Link Extension staying on In conditions where groundwater target to open on schedule,” Davidson was present, ground freezing was per- said. “Following on from the success- formed to allow cross passage excava- ful U-Link project it’s been great to see tion in a watertight zone. This marked the continuing expansion of rail tran- the first time that Sound Transit had sit options in the region.” used ground freezing on its projects. “Overall the tunneling went well,” In addition to cross passages, ground Capka said. “When we were develop- freezing was used to create a support - canopy f eak-in into the len Jacobs Associates, we said we tar- University District Station site. geted a tunnel contract start in 2013 Ground freezing was used on 11 of and finish in February 2018. With the 23 cross passages, 5 using vertical all the complex conditions we faced drilling from the surface and 6 using with tunneling and some of the unan- horizontal drilling from within the ticipated challenges that came up, we completed tunnel. Original plans finished in February 2018. Keeping had been to dewater the 6 locations to that schedule is crucial in allow- of horizontal ground freezing, but ing our follow-on contractors to start Next Phase of actual ground conditions encoun- their work and mak te Link tered rendered the dewatering op- Extension a reality.” Tunneling tion not feasible.