The History of Tunneling at PB
A Look at Milestone Projects Spanning the Firm's 125 Years

George Munfakh

In 1885, William Barclay Parsons established a consulting engineering practice at 22 William Street in Lower Manhattan. Since then, PB has continued to play leading roles on transportation, power, buildings, and environmental projects throughout the world.

During its 125-year history, PB has participated in the development of the first mass transit systems for New York City, San Francisco, Atlanta, Taipei and Singapore; the advancement of immersed-tube tunnel technology; and various innovations in the design and construction of bridges.

One of the first undertakings of Parsons’s new venture was the design of a subway system for New York City in the 1890s. And from the first IRT line, which opened in 1904, to the current extension of the No. 7 line and the new Second Avenue Subway, PB’s service to the New York City subway system has spanned its entire 125-year history.

“We designed the first subway here and more than 100 years later we are still playing a major role in planning, designing, building and maintaining the critical transportation infrastructure this city needs to prosper for the next 100 years,” Chief Executive Officer George J. Pierson said.
As part of its observance of PB’s 125th anniversary, George Munfakh, Director of PB’s Geotechnical & Tunneling Technical Excellence Center, was asked to review PB’s history in tunneling. Munfakh covered various tunneling technologies including cut-and-cover, immersed tunnels, mined/bored tunnels and geotechnical innovation.

Munfakh’s comments appeared in the firm’s publication NOTES, and is being reprinted below with permission.

From the first segment of the New York City subway, for which William Barclay Parsons, the founder of the firm, was Chief Engineer, to the firm’s current work designing and managing construction of extensions to that system, PB has participated in the design and construction of some of the longest, largest, deepest and most complicated tunnels in the world. PB's tunnels have been built in hard rock, soft ground or mixed-face conditions, using mining, boring, jacking, cut-and-cover, and immersed tube technology.

Cut-and-Cover Tunnels

One of the earliest uses of cut-and-cover tunneling in the United States was in connection with the initial segment of the New York City subway, which opened in 1904. To reduce the construction cost and schedule, and facilitate quick entry and exit of passengers from the subway, Parsons elected to build shallow tunnels using cut-and-cover technology, which was ideally suited to the geology of Manhattan, as opposed to the deep mined tunnels of the London Underground, the world’s first subway.

Parsons developed a means of cut-and-cover tunneling in which one side of the street was excavated, the tunnel box constructed inside, and then covered up and opened to normal traffic while work proceeded on the other half of the street.

From the early 20th century to today, PB has refined and improved cut-and-cover techniques so that subways can be constructed with minimal adverse impact on buildings, utilities, neighborhoods and the environment. A few examples:

• Pioneering use of the SPTC (soldier pile-tremie concrete) wall on San Francisco’s BART (Bay Area Rapid Transit) in the 1960s allowed deep excavation in a highly seismic urban area.
  
• Design of slurry walls as permanent structures allowed the Harvard Square Station in Cambridge, Mass., constructed in the 1970s, to be shoehorned between two buildings on the National Register of Historic Places.
  
• First use of jet grouting on a subway system, which allowed Baltimore Metro’s Shot Tower Station to be constructed without interrupting high-voltage electric lines that cross the excavation.
  
• Design of a combination of slurry diaphragm walls and jet-grout walls at the 63rd Street Queens Connector in New York City allowed safe underground construction in the vicinity of contaminated plumes.

Mined/Bored Tunnels

PB’s earliest mined tunnels were designed by William Barclay Parsons for the New York subway in the 1890s. Sections of mined tunnel included a 2-mile long tunnel in the Washington Heights section of Manhattan and a stretch along Park Avenue. For the Steinway (Queensboro) Tunnel under the East River, Parsons decided to go deep and use mined tunneling. He erected a large working platform on a rock outcrop in the East River, sunk two shafts from the rock island as well as shafts on each bank of the river, and drove four headings at once. The tunnel, through which the No. 7 train now travels, was completed in 1907.

A mined tunnel under the Scheldt River in Antwerp, Belgium, built in the early 1930s, posed unusual challenges, including difficult ground conditions. To facilitate excavation of a deep shaft from which mining of the tunnel would begin, the saturated and running soil was frozen, an innovative concept considered novel even by today’s standards. Despite the many challenges, the firm completed the job in just 18 months.

In the 1980s, on behalf of the Canadian Pacific Railroad Company, PB designed the Mount MacDonald Tunnel, a 9-mile long rock tunnel that crosses Rogers Pass in Western Canada and was, at the time, the longest tunnel in the Western Hemisphere.

Vehicular mined tunnels to which PB made significant contributions include the Glenwood Canyon Tunnel in Colorado (1992); the Tetsuo Harano tunnels of Hawaii’s H-3 highway (1994); and the Cumberland Gap Tunnel in Kentucky, Tennessee and Virginia (1996). All three featured context-sensitive designs that met strict environmental requirements.

Mined Caverns

During the Cold War, PB pioneered methods for the creation of large underground spaces for military fortresses. The firm’s work in this area began in the late 1940s with the design of a hardened underground defense facility at Fort Ritchie, in the Catoctin Mountains near Waynesboro, Pa., and culminated in the early 1960s with NORAD (North American Air Defense Command Center), an underground cavern deep within Cheyenne Mountain outside Colorado Springs, Colo., comprising six huge chambers and several tunnels designed to sustain nuclear attack. Recently, mined caverns have been designed by PB for construction of transit stations or underground storage.

Immersed Tunnels

An early application of immersed tunneling in the United States was the 1-mile vehicular tunnel between Detroit, Mich., and Windsor, Ont., completed in 1930. The Detroit-Windsor Tunnel has three sections: open approaches, shield tunneling from the approaches to the river and an immersed tunnel under the river. The immersed tunnel segments featured the first use of welded steel shells and internal steel lining in tunnel construction. It was also the first tunnel designed and built by PB.

From designing the original New York City subway to current expansion projects like the East Side Access, PB has been a leader in tunneling projects worldwide for more than a century.

Other immersed tunnels designed by PB included the Baytown Tunnel under the Houston ship channel in the early 1950s; a number of tunnels in Virginia over a period of 30 years including the first Elizabeth River Tunnel (also known as the Downtown Tunnel) connecting Norfolk and Portsmouth, opened in 1952; the Midtown Tunnel, completed in 1962; and the second Downtown Tunnel, opened in 1982. The standouts, however, were the PB-designed bridge-tunnel crossings of Hampton Roads, Va., completed in 1957 and 1976, respectively. For those projects, immersed tunnels were built between two artificial islands that connected to the mainland via bridges.

Another notable immersed tunnel was the Fort McHenry Tunnel, completed in 1985, which was the widest immersed tunnel built at that time and the first to have double tubes, carrying a total of eight lanes of traffic, laid immediately side-by-side in a single trench under Baltimore Harbor.
An immersed tube tunnel under San Francisco Bay constructed in the late 1960s as part of BART was the longest and deepest immersed tunnel built at that time. It was also the first immersed tunnel to use cathodic protection for corrosion control, and to be designed for seismic conditions using a triaxial seismic joint between the tube and its land connection. The BART tunnel suffered no damage as a result of the devastating Loma Prieta earthquake of 1989, and following the disaster was the only direct means of public transportation between Oakland and San Francisco.

Internationally, PB’s immersed tunnel experience includes Hong Kong’s first cross-harbor tunnel, linking Hong Kong island to Kowloon, for which PB in the early 1970s developed a replacement steel design for a tunnel originally designed as a concrete box. In the 1990s PB designed an immersed concrete tube for the Western Harbor Crossing, which was part of an effort to improve access to Hong Kong’s new international airport.

Water Conveyance Tunnels

Water conveyance tunnels for which PB has performed design or construction services include:

• The 9-mile Boston Harbor outfall and its 55 state-of-the-art diffusers (completed in 2000), which was part of the effort to clean up Boston Harbor;
  
• The recently completed Singapore Deep Tunnel Sewerage System, a project that replaced that country’s entire wastewater treatment system, 30 miles of tunnels; and
  
• The design of water conveyance tunnels of the Croton water treatment plant in the Bronx, N.Y., and the ongoing rehabilitation of 31 miles of the New Croton Aqueduct of the New York City water supply system, which was built in 1885, the year PB was founded.

Ground Improvement

Sometimes, before tunnels can be dug, or while they are being excavated, the ground through which they pass must be stabilized or otherwise improved to allow for smooth tunneling with minimal impact on adjacent structures and utilities. Over the past three decades, PB has developed a number of ground improvement techniques that have facilitated tunneling on projects including the following:

• Chemical grouting allowed tunneling on the Lexington Market section of the Baltimore Metro about 7 ft beneath a 19th century brick-lined tunnel.
  
• Soil nailing made possible the construction of a tunnel portal for the West Side light rail line in Portland, Ore., at a site susceptible to landslides.
  
• Ground freezing allowed tunneling of Cleveland’s Heights Hilltop Interceptor through an active railroad embankment.
  
• A combination of jet grouting and micro piles expedited construction of MARTA tunnels under Interstate Highway I-285 in Atlanta.
  
• Jet grouting and fracture grouting at the 63rd Street Queens Connector in New York City allowed for the tunnel excavation beneath an existing tunnel and elevated railway.
  
• Geomembrane incorporated within the tunnel lining design facilitated safe tunneling through petroleum-saturated ground along the Los Angeles Metro Red Line.
  
• Ground freezing of soil under active railroad tracks at Boston’s South Station allowed contractors on the Central Artery/Tunnel project to jack huge vehicular tunnels through unstable soil without interrupting rail traffic above.