Survey Transportation Tunnels in Greater Boston capacity of public transportation in the Boston A summary of all major trans­ area. In 1888, there were more than eight thou­ sand horses pulling streetcars in Boston. The portation tunnels in the Boston many rapid transit facilities built since that area, with notes on how their time (Woodhouse & Barosh, 1991; Clarke & Cummings, 1997; Cheney, 2002; Cudahy, 2004; construction added to under­ McKendry, 2005) formed the foundations of standing Boston's geology. today's Red, Orange, Blue, Green and Silver subway lines of the MBTA (see Figure 6-1). This subway network, now 125 kilometers DAVID WOODHOUSE & PATRICK J. BAROSH (77.4 miles) in length, carries an estimated 250 n order to accommodate Boston's growth, million riders annually, and has planned and to facilitate commerce, a number of extensions. The system includes 50 kilometers Ipublic works have been designed and con­ (31 miles) of active subway tunnels. For a met­ structed since the late nineteenth century. ropolitan area the size of Boston, its rapid Tunnels have been built for vehii:ular traffic as transit system is large when compared to well as for mass transit. The tunnels have rapid transit facilities elsewhere in the United largely been excavated by means of open-cut States. Boston has 1ong been a leader in rapid excavations, with notable exceptions for the transit development, starting with America's trans-harbor crossings and the Massachusetts first subway part of the Green Line, which Bay Transportation Authority (MBTA) Red . opened in 1897, and the second undersea tun­ Line extension through Porter Square, nel, the East Boston Tunnel on the Blue Line, Cambridge. Tunnel excavations offer a unique put in service in 1904. Both lines remain in opportunity tq examine soil and rock over a daily use and are augmented by the area's long cross-section not always afforded by commuter rail system. The subway tunnels building excavations. were largely constructed by cut-and-cover methods with three notable exceptions. Subway Tunnels Early Subway Construction History. A three­ More than a century has passed since state person Board of Subway Commissioners, and local governments in Massachusetts first subject to approval of the Boston City Council recognized the need for decreasing street con­ and appointed by the mayor, was created in gestion and for increasing the speed and 1893 by the state legislature to report on the CIVIL ENGINEERING PRACTICE 2011/2012 295 FIGURE 6-1. Map of the Boston area showing routes of the MBTA system, July 2011. feasibility of building a subway under Boston During the fall and winter of 1894-1895, the Common for the purpose of removing street­ engineering staff of the Boston Transit car traffic from Tremont Street. The council Commission took the Tremont Street Subway gave its consent, and the board was appoint­ from the planning phase to final design. Ground ed on January 1, 1894. After hearing from crit­ breaking took place on March 28, 1895, at a pub­ ics and supporters of the subway, various lic ceremony presided over by the governor. technical experts in the construction, trans­ Work progressed so rapidly that the first Tremont portation and health fields, as well as from Street section beneath Boston Common was proponents of elevated railways, the legisla­ opened on September 1, 1897, from Park Street to ture enacted a bill on July 2, 1894, to create the a portal in the Public Garden, near Arlington and Boston Transit Commission and the Boston Boylston Streets. (see Figure 6-3). Two additional Elevated Railway Company. The Boston segments of subway were opened later. The leg Transit Commission would be a governmen­ under Tremont Street from Boylston Street tal body whose primary function would be to Station to Pleasant Street (now Br~adway in the construct the Tremont Street Subway, now · Boston South End) opened on October 1, 1897, part of the Green Line (see Figure 6-2). The and on September 3, 1898, operations com­ Boston Elevated Railway Company, on the menced on the final section to Haymarket near other hand, would be privately owned and North Station (Whitehill, 1968) for streetcar traf­ charged with building elevated lines. The leg­ fic. The Haymarket end of the tunnel was con­ islation required a local referendum, and nected by an elevated loop that circled to the east Boston voters overwhelmingly approved the above Atlantic Avenue to connect South and bill on July 24, 1894. North stations in 1901 (see Figure 6-4). 296 CIVIL ENGINEERING PRACTICE 2011 /2012 FIGURE 6-2. Map of the Tremont Street subway (Green Line) showing gradual extensions . and their dates of completion. (Courtesy of spuimap.) The original Boston Elevated Railway Act December 4, 1908, streetcar service fully of 1894, which was amended in 1897, provid­ resumed through all parts of the subway that ed for a transit tunnel under Boston Harbor to were formerly used by the high-platform East Boston and the Boston segment of a sub­ trains of the elevated system. way to Cambridge. The East Boston Tunnel, The Boston Elevated Railway and the the first underwater transit tunnel in North Boston Transit Commission shared joint America, opened for streetcar traffic in 1904. responsibility for constructing a line to connect The tunnel, now part of the Blue Line, extend­ Park Street in Boston with Harvard Square in ed from Maverick Square, East Boston, to Cambridge. This line consists of a cut-and­ Court Street Station, near Scollay Square (now cover Cambridge Tunnel from Harvard that Government Center) in downtown Boston rises on the Longfellow Bridge, crosses over and allowed passenger transfer to the elevated the Charles River and then runs through a train at a midway station at Atlantic Avenue shield-driven, hand-mined tunnel under and State Street. Beacon Hill and under the Park Street Station. A 2 kilometer (1.23 mile) long subway tun­ This segment is now part of the Red Line (see nel was then dug under Washington Street Figure 6-1). The Cambridge section was built between 1905 and 1908 for the Sullivan­ by the Boston Elevated Railway, but all sec­ Dudley line and replaced the use of the tions in Boston were built by the Boston Transit Tremont Street Tunnel for service to Dudley Commission. Construction in Cambridge start- . Square. The Washington Street Tunnel, which ed July 12, 1909, on the first segment and the follows the old Boston Neck, was opened for subway began operation on March 23, 1912. public use on November 30, 1908. Removal of An extension to South Station, known as the high-platform and third-rail equipment (the Dorchester Tunnel, opened on December 3, third rail was never used) from the Tremont 1916. A further extension, which opened on Street Subway began at once, and on June 29, 1918, continued southward through a CIVIL ENGINEERING PRACTICE 2011 /2012 297 FIGURE 6-3. Construction trench for Tremont Street subway circa 1896. (Courtesy of the Society for the Preservation of New England Antiquities.) tunnel under Fort Point Channel to reach mont Street Subway near the Public Garden Andrew Square in South Boston. Incline to a portal in Governor Square, now The need for rapid transit service in the Kenmore Square (see Figure 6-2). As part of congested Back Bay area led to a proposal to the subway construction, the incline itself construct a new subway line, which was would be shifted to the middle of Boylston approved by the state legislature in 1907. The Street, parallel to its old location. The subway bill specified that the facility be built under the opened on October 3, 1914. Charles River Embankment and be kno,·vn as A short extension of the East Boston, street­ the Riverbank Subway, with stations located car based subway system took place between at Charles Street, Dartmouth Street and Mas­ 1912 and 1916. The East Boston Tunnel, when sachusetts Avenue. The Boston Elevated Rail­ originally opened, ran downtown to Court way strongly opposed the location of the Street Station, which was a stub-end single­ Riverbank Subway, and abutting property track terminal. Traffic volume through the owners, who were worried about the effects tunnel increased tremendously over the years, that the construction of the subway would and this single-track tum-back became an have on sewers and other underground utili­ operational nuisance. The answer was a short ties, joined together and protested to the legis­ 796 meter (2,610 foot) extension to Bowdoin lature. The protest succeeded and in 1911 the Square. The tunnel runs through the deformed lawmakers abandoned the Riverbank Subway Pleistocene soil deposits of Beacon Hill in favor of a line beneath Boylston Street. The (Boston Transit Commission, 1913; Kaye, Boylston Street Subway, now the Green Line, 1976b), where an underground station, a loop began construction in March 1912 for a two­ and a surface incline to Cambridge Street were track cut-and-cover tunnel, which would built. The loop allowed a quick turnaround for eventually run from a connection with the Tre- streetcars from East Boston, while the incline 298 C IVTT. F.r..:CL'\IEERJNt; PRACl'ICE 2011/ 2012 permitted cars to come to the surface and travel all the way through from Cambridge to East Boston. Streetcar tracks were laid across the Longfellow Bridge along with the sub­ way in the center. The East Boston Tunnel Extension was opened on March 8, 1916. The Boston Transit Commission had by this time opened the East Boston Tunnel and its extension to Bowdoin, the Washington Street Tunnel, the Boylston Street Subway and the Tremont Street Subway. In the late 1930s, the Boston Transit Department (which succeeded the Bos­ ton Transit Commission in 1918) began the Hunting­ ton Avenue Subway (see Figure 6-2), now a branch of the Green Line, through a variety of deposits (Aldrich & Lambrechts, 1986).