tunnels Archives - Infrastructure Digest

Sinking Soils Further Impede Efforts To Extricate Alaskan Way Viaduct’s Stuck TBM

Differential settlement of more than an inch has temporarily shut down efforts on the already-stalled Alaskan Way Viaduct project under downtown Seattle. Excavation had been underway on an access pit that was designed to repair “Bertha,” the stuck tunnel-boring machine (TBM), as crews continue to monitor the movement on surrounding buildings.

The 57.5-ft-dia machine has been stuck since December 2013, just over 1,000 ft into its 1.7-mile route under downtown Seattle as part of an effort to replace the aging viaduct after settlement was first detected a month earlier (ENR 2/24 p. 21).

Why should you read this? Schadenfreude? ENR, December 2014

Tunnel Beneath the Bay

“The new pipe will be installed in a dedicated tunnel constructed roughly 100 feet below the bay floor. Known simply as the “Bay Tunnel,” the new conduit is 15 feet in diameter and more than five miles long. The digging is done by an earth pressure balance tunnel-boring machine (TBM), a type of tunneling system well suited to the dense clays that make up much of the bay floor. To launch the TBM, the project’s tunnel contractor, Michels/Jay Dee/Coluccio Joint Venture (MJC) excavated a shaft 58 feet in diameter and 124 feet deep in East Menlo Park on the west side of San Francisco Bay.

According to MJC Project Engineer Ed Whitman, the TBM and launch shaft are normal parts of a major tunneling project. But the Bay Tunnel contains an important distinction from Whitman’s past projects. In other TBM-built tunnels, several vertical access shafts (Whitman calls them “manholes”) are built at intervals along the tunnel. In a similar sized-tunnel that Whitman worked on in Ohio and California, manholes were spaced roughly 1,000 to 1,500 feet apart. Among other functions, the shafts enable project surveyors to connect geodetic control points on the surface to the control points in the tunnel, making adjustments and corrections as the TBM moves ahead. Because the Bay Tunnel is under a body of water, manholes aren’t possible. As a result, all the survey control (essential to steering the TBM) is tied to one end of the tunnel. “It’s like taking a five-mile shot off a 50-foot backsight,” says Whitman. “From the survey perspective, it’s not for the faint of heart.””

Why should you read this? If tunneling 100 feet under San Francisco Bay doesn’t get you interested… maybe you shouldn’t be in infrastructure? POB, January 2013

Japan Orders Inspections After Fatal Tunnel Collapse

“Revelations that aging bolts and rods may have led to the devastating highway tunnel collapse that claimed at least nine lives in Japan over the weekend has sparked nationwide anxiety over the safety of decades-old infrastructure.

Thus far, a total of nine bodies have been pulled out from the debris of a fallen highway tunnel, built in the 1970s, the Yamanashi prefecture police said on Monday.”

Why should you read this? Japan’s not the only country with aging infrastructure… is this a preview of the coming global situation? Includes video and slideshow. Wall Street Journal (blog), December 2012

Patented Precast Shaves Costs on Korean Highway

“Freyssinet’s $30-million subcontract entails building the tunnel in an open trench. The technique, patented by its subsidiary Tierra Armada S.A., involves assembling precast-concrete tunnel arches in halves and backfilling to finished ground level. The three-pin arches support the earth above in compression. Cast in three-meter lengths, the 40-centimeter-thick arches rise nearly eight meters from the tunnel’s 1.2-m-tick reinforced-concrete base slab and span 12.6 m each. Once placed, the opposing arch halves abut at the crown, propping each other in position.” Innovative tunnel case study with gratifying detail. ENR, July 31st, 2012

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