Tunnel Business Magazine

DEC 2018

TBM: Tunnel Business Magazine is the market leader for North America. TBM is written for leading professionals in all aspects of tunneling and covers project stories, design elements, contracting strategies, legal issues, new technology and more.

Issue link: http://digital.tunnelingonline.com/i/1067144

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Page 20 of 59

TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // DECEMBER 2018 F E AT U R E S T O R Y 2 1 ored through the earth, it dispersed an annulus grout – the cementitious grout that is placed between the concrete seg- mental liner and the ground. The grout fills this gap and holds the con- crete liner in place. The grout needs to be pumped for long distances and exhibit good stability. Therefore, the workers on site use ebent CBS 5, a sodium bentonite mixture, to keep the grout from segregating and setting too quickly equick CBS System 1, which allowed the grout to be pumped for long distances without setting. Once the grout reached the point of placement, it needed to set quickly. The sodium sili- ca equick CBS System 2 was used to produce a rapid set, typically in 5 to 10 seconds. The ground that is being mined is often treated as it is being excavated in order to facilitate the extraction and removal of the spoils (soil, dirt and rubble). For the ART proje ovided Polyfoamer FP/CC, which is foamed before being injected into the ground. It works to reduce the stickiness of the clay that the tunnel boring machine passed through and to provide body to the coarse sands and silts. b T group were on hand to consult with the proj- ect engineers and workers and to ensure tha products was optimal for the ART proje ored 100 ft (30.5 m) underground, passing under the Anacostia River, CSX railroad tracks, and the Green Line of the Washington, D.C., subway system. The joint venture team of Impregilo/Healy/Parsons was awarded a $254.9 million contract for completion of the tunnel and shafts. The proj- ect was delivered using design-build and featured the extensive use of slurry walls, and included depressurizations of lower artesian aquifer while leaving upper aquifer undisturbed. vance used conveyor belt system through multiple curves with a vertical belt storage unit exterior to the shaft. Other unique fea- tures included: steel fiber precast segmental lining; extensive use of geo- technical instruments f cavation performance; and use of compensation grouting to cross under fragile critical utilities. "Nannie" Quick Facts • Herrenknecht 26-ft dia. EPB • Approximate $25M cost • Named after educator and civil rights leader Nannie Helen Bur- roughs • Mining start: 10/29/15 • Mining end: 11/5/16 • Bolted and gasketed concrete steel fiber reinforced segments • Seven piece ringset, 12" thick by 6 foot long • Best mining day = 138 feet (23 rings) • Average = 39 feet per day

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