Courtesy of ARUP by QA Photos/Rail Link Engineering

Making The Case For Tunnels

All over the world there are invisible construction projects in progress that have important consequences. Tunnel engineers are planning and building enormous structures to meet underground transportation and water/wastewater needs. In California, for example, the San Diego County Water Authority’s $827-million Emergency Storage Project involves a dam, pipelines, and tunnels. The San Vicente Pipeline, scheduled to begin in late 2004, will involve a 12-mile tunnel, 12-ft wide, running between 100 ft and 600 ft below ground, and including an 8-1/2 ft pipeline.

Courtesy of San Diego County Water Authority

What’s driving current underground projects? George Yoggy, president, and Susan Nelson, executive director, of the American Underground Construction Association, jointly offer this view: “In past times, there were many constraints on where and whether a tunnel could be constructed. Due to advances in tunneling technology and new equipment and materials used in tunnel construction, it is now possible to build a tunnel safely in any situation. This has freed potential tunnel owners to plan projects which were not possible even 20 years ago. Consider the St. Clair River Tunnel, a new rail tunnel linking Canada and the U.S. The large-diameter, near-surface tunnel was constructed in difficult ground beneath the river and sensitive structures with only minimal ground movements.

Putting Costs Into Perspective

Courtesy of DMJM+Harris © Andy Ryan

“The major constraint to construction of underground facilities is that the construction cost is nearly always more than for surface facilities. Rarely do decision-makers evaluate the life-cycle cost of underground facilities against their alternatives. If they did, they would find the advantages of putting facilities underground more than compensate for the higher initial expense. [These] advantages include preserving the surface for a higher use and improved efficiency of urban centers, especially when transportation projects are located underground. There are secondary advantages such as improved air quality due to reduced surface congestion, reduced noise pollution, reduced accident rate between pedestrians and vehicles due to grade separation—all of which enhance the surface environment.”

Yoggy and Nelson suggest that going underground for transit, rail and highway projects would make room on the surface for commercial and retail purposes that could generate revenues far in excess of the cost of building a tunnel.

“Technology is available to build tunnels and underground structures safely, anywhere. What is needed is for us to help decision-makers realize that the higher initial cost of an underground facility is a worthwhile investment which will immediately and over the life of the project improve the surrounding area and which may allow the freed surface to become a revenue-generating proposition.”

New Reasons To Go Underground

Courtesy of DMJM+Harris © Andy Ryan

George E. Williamson, of Traylor Brothers, and director of the Rapid Excavation & Tunneling Conference for the Society of Mining Engineers, contributes news of an improved climate for tunnel construction: “The most significant technical advancement in U.S. tunneling has been the use of pressurized face tunnel shields that allow tunnels to be constructed in soils below the water table that would not have been considered possible a decade ago. This method involves the use of either a slurry shield or an earth pressure balance shield, along with high-precision, precast, bolted and gasketed segmental concrete lining.

“A significant commercial improvement has been the inclusion of a Geotechnical Baseline Report, along with a Disputes Review Board and the partnering process in tunnel contracts. The use of these features has led to open communications between the parties (client, designer, construction manager, and contractor) and timely resolution of disputes. Tunnel contractors for the most part endorse the use of the features, as it shows that the client has chosen a reasonable approach to risk allocation, and chances are good that he will be treated fairly.”

Courtesy of DMJM+Harris © Andy Ryan

Innovation saves. And on the MBTA’s South Boston Piers Transitway Project, Paul Roy (DMJM+Harris) and his tunneling team partnered closely with the MBTA to develop innovative tunneling solutions that not only saved money, but preserved history.

A 3-mile-long underground transit system connecting Boston’s central business district with the developing piers and South Boston, the Transitway contained a critical construction juncture on and under Russia Wharf. On that site, its three significant buildings—known as the Russia Building, the Graphic Arts Building, and the Tufts Building—could not be moved, altered, or closed during tunneling.

These seven-story, steel/masonry, barrel-arch structures are pile-supported on granite caps. Determining that conventional underpinning methods would hurt the protected, historic complex and increase project costs, tunneling veteran Roy and his team instead elected to construct 400 ft of tunnel beneath the occupied historic structures, utilizing ground-freezing technology with shotcrete-supported mining techniques.

Agreeing that this process would have the “least impact to the fabric of the buildings,” the Massachusetts Historical Commission gave the MBTA and Roy permission to proceed. Despite extraordinarily close quarters, Roy and his team successfully delivered the tunnel without any impact to these fully occupied buildings.
Roy and his team provided great comfort to the MBTA and the citizens of Boston by helping to preserve their history. Their success led MBTA officials to say that “DMJM+Harris’s ability to identify innovative construction methods (this was, after all, the first U.S. utilization of ground freezing to underpin an historic landmark while tunneling underneath) has been outstanding.”

Once regarded as a marvel of railroad engineering, a narrow concrete and blue trap-rock canyon of train tunnels and trenched railbeds, the Bergen Arches and Erie Cut was built between 1906 and 1910, to run through the hills of the lower Palisades. Today, the Bergen Tunnel and the four tracks carrying nearly 24,000 riders a day are under renovation. The work is being performed through a joint venture between Merco, Inc. of Lebanon, NJ, and Japan’s Obayashi Corporation.

The 4,400-ft North tube of the tunnel lies 75 ft below the surface, and over the years moisture leaked into the tunnel. During winter months, icicles formed and fell on the catenary wires, sometimes knocking out service.

In July 2001, Merco/Obayashi began blasting the rock to enlarge the tunnel by 6 in. After the rock was blasted, a layer of shotcrete was applied, using a Meyco Supreme shotcrete robot, to stabilize the tunnel. According to Mike Mergentime of Merco, the Swiss-made, radio-controlled robot is one of the first of its kind to be used in the U.S. A PVC membrane was affixed to the walls for waterproofing, then reinforcing steel was installed. At that point, a traveling form, made by EFCO, was erected.

Clyde Joseph, vice president of engineering for Merco, solicited bids on tunnel placers and chose Con Forms Tunnel Placers, made by Construction Forms, in Port Washington, WI.

Merco purchased two 5-in. powered tunnel placers with scissor cart assemblies in order to pump concrete from both ends of the tunnel. Con Forms engineers worked directly with EFCO on producing placers that would be exactly suited for the forms. Eastern Concrete feeds ready-mix into a Putzmeister 1408 trailer pump, and a Reed 3120 trailer pump to the Con Forms placers, which pump into ports placed 5 ft apart in the form. The hydraulically powered, telescoping boom rotates 180 degrees, to reach wall and ceiling ports in the form.

After the mud mat is poured, the arch and track slab are poured. Standard ballast-and-tie track is being replaced with a direct fixation track, with rails sitting on a plate cast in concrete. Merco/Obayashi is scheduled to be finished with construction by February of 2003, with rail service in place by April.

The new rail link between London and the Channel Tunnel, involving ARUP in the development and design, is continuing. Phase 1, the North Downs tunnel, is now complete. Phase 2, underway now, involves eight tunnel-boring machines, of which three are currently in the ground. One tunnel runs 17 km below London through varying ground conditions and water pressures up to 3 bar. Another is 3.2 km through chalk below the River Thames.

In New York City, ARUP, in a joint venture with DMJM+Harris, is responsible for concept design and preliminary engineering for New York City Transit’s Second Avenue Subway.