Canton Viaduct
Canton Viaduct is the oldest railroad bridge of its kind in the world and it was the longest and tallest railroad bridge in the world when it was built in 1835. It is the only blind arcade cavity wall bridge in the western hemisphere and has been in continuous service for 174 years; it now carries high-speed passenger and freight rail service. This hollow bridge in Canton, Massachusetts, (USA) was built by Scottish Freemasons in 1835 for the Boston and Providence Railroad Corporation (B&P). The bridge is 0.3 miles (0.5 km) south of Canton Junction and originally provided mainline service between Boston, Massachusetts, and Providence, Rhode Island. It was the final link to be built on the 41-mile railroad between the two cities. The viaduct is located on Amtrak's Northeast Corridor at milepost 213.74, reckoned from Pennsylvania Station in New York City, and at the Massachusetts Bay Transportation Authority's (MBTA) milepost 15.35, reckoned from South Station in Boston.

Inception
The Canton Viaduct was erected in 1835 by the B&P, one of the first New England railroads, shortly after its 1831 founding. Thomas B. Wales, one of the original families of Boston, and owner of the T.B. Wales & Co. Shipping Company, was the first president of the B&P, The Taunton Branch Railroad, as well as the Western Railroad Corporation. Due to his friendship with prominent New England families, including the Revere family, they were able to bring the Canton Viaduct to fruition. The T.B. Wales & Co. clipper ships brought raw materials for manufacturing companies from its dock (Wales Wharf) and Counting House (Long Wharf) to various areas in New England. Without the influence of individuals such as Thomas B. Wales, Joseph Warren Revere, owner of the Revere Copper Company and major stockholders (most of whom were Board members), the Canton Viaduct would not have been built. There were better routes through other towns for the location of the railroad line from Boston to Providence. However, building the railroad through Canton placed the line close to Paul Revere's Copper Rolling Mill, where a half mile spur (using strap rails and horse power) connected the mill to Canton Junction and undoubtedly gave a boost to Revere's copper business. The other influencing factor that caused the Canton Viaduct to be built was a fatal accident in 1832 on the Granite Railroad, which used inclined planes to cross a valley. The original plans called for the use of inclined planes to cross the Canton River Valley, but they were changed after the inclined plane accident, and a bridge was built instead. This unique bridge was designed by a U.S. Army Corps of Engineers Officer and West Point graduate - Captain William Gibbs McNeill. He was assisted by engineers, Major George Washington Whistler (McNeill's brother-in-law), Major General Isaac Ridgeway Trimble and General William Raymond Lee. The bridge was built by the Dodd & Baldwin company from Pennsylvania. Around this time, Russia was interested in building railroads. Tsar Nicholas I sent workmen to draw extensive diagrams of the Canton Viaduct. He later summoned Whistler to Russia as a consulting engineer to design the Moscow–Saint Petersburg Railway, on which two bridges were modeled after the Canton Viaduct. A scale model bridge of similar design is on display at the Oktyabrsky Railroad Museum in St. Petersburg.

Design and construction

Classification
The bridge resembles an ancient city wall built from rusticated stone, supporting a train deck about 60 feet (18 m) above the Canton River, the east branch ( tributary) of the Neponset River. The stream pool passes through six semi-circular portals in the bridge, flowing to a waterfall about 50 feet downstream. The bridge is an archetype due to its blind arcade and cavity wall combination, the first and possibly only time these two elements were used in bridge design. The structure is often referred to as a "multiple arch" bridge, but the deck arches are not the primary support system. Although the deck arches appear to extend through the bridge to the deck arches on the opposite side, they do not; each deck arch is independent and only four feet deep. The only arches to penetrate the walls are six river portals and two roadway portals. Since bridges are classified by their primary support system, the Canton Viaduct is more accurately described as a blind arcade cavity wall. The walls support the majority of the deck with stone slabs spanning the cavities. The deck arches only support the outer limits of the deck (beyond the walls); they are tied to the walls but do not penetrate them. The coping is supported by 42 segmental deck arches (21 on each side) that join the tops of 22 buttresses tied to the continuous walls internally and externally. The walls are five feet thick with a four foot gap between them joined with occasional tie stones. More construction details are available in the original specifications. When the bridge had a single set of tracks, the rails were placed directly over the walls as the cavity's width is less than standard gauge. When the bridge was double tracked in 1860, the inside rails were placed directly over the walls and the outside rails were over the deck arches. The Thomas Viaduct (Maryland, 1835) and Starrucca Viaduct (Pennsylvania, 1847) are classic examples of multiple arch viaducts, as their primary support system consists of semi-circular arches on piers without any walls.

Materials
The Canton Viaduct contained 14,483 cubic feet (15,800 perches) of granite, which weighs approximately 66,000,000 pounds (33,000 short tons) prior to its concrete redecking in 1993. Each stone has a Mason's mark to identify who cut the stone. Each course is 22" - 24" high and laid in a pattern closely resembling a Flemish bond. Exterior stone for the walls, buttresses, wing wall abutments, portals, deck arches, coping, parapets and the foundation stone are riebeckite granite mined from Moyles quarry (a.k.a. Canton Viaduct Quarry) located on the westerly slope of Rattlesnake Hill in Sharon, Massachusetts; now part of Borderland State Park. This type of granite was chosen because it does not stain as it weathers, but retains its original color. Interior stone for the foundation, walls, buttresses, wing wall abutments, binders, stiles, deck and the Cornerstone are of a different type of granite mined from Dunbar's quarry in Canton, Massachusetts.
  • Granite (two types from two local quarries)
  • Mortar (except interior of the wing wall abutments which were laid dry)
  • Reinforced concrete (roadway portal and deck arches)
  • Reinforced concrete (new deck and cross ties)
  • Waterproof cement (on coping stones)
  • Iron (fence/railing and rails)
  • Galvanized steel (walkway grating and catenary system)
  • Rubber (ballast mats under tracks for noise reduction)
  • Lean concrete (longitudinal troughs fill)
  • Crushed granite ( track ballast)
  • Wood (original longitudinal sleepers, cross ties, fence/railing and curb)


Location
The majority of the viaduct is over land (71%), while 29% is over water. In addition to the six river portals, one roadway portal was originally provided. The distance between the buttresses at this section is wider than all the other sections of the bridge. The overall length is 615 feet (187 m) with a one degree horizontal curve that creates two concentric arcs. This makes the west wall slightly shorter than the east wall producing a slight keystone shape in the cavities. Originally unnamed, it was referred to as "the stone bridge" and "the viaduct at Canton" before it was eventually named after the town. In 1840 the road under the viaduct was known as "the street leading from Neponset Bank by Elisha White's to near Joseph Downes. Sometime after, it was known as "Rail Road St.", and in 1881, it was finally named "Neponset St." after the river. It serves as a major artery in Canton connecting its main street (Washington St.) to Interstate 95.

Freemasons
The stonecutting and finish masonry was performed by Scottish (Operative) Freemasons who camped at Dunbar's Quarry in Canton, Massachusetts. The Scottish Freemasons were considered artisans and most likely belonged to the Rising Star Lodge in Stoughton, Massachusetts. The rough masonry and construction of the gravel roadbed was performed by Irish workers, who camped at Dunbar's ledge in Canton, Massachusetts. Construction The Canton Viaduct cost US$93,000 to build in 1835, which equates to $2.4 Million in 2009 dollars. Construction took 15 months, 8 days from laying of the foundation stone on April 20, 1834 to completion on July 28, 1835. An excerpt from an article in the Providence Journal on June 6, 1835 describes the bridge prior to its completion. As reported by the Boston Advertiser and the Providence Journal. "Whistler" was the first engine to pass over the entire length of the road. The engine was built by Robert Stephenson in 1833 in England and named by William Gibbs McNeill in honor of his brother-in-law George Washington Whistler. The trip from Boston to Providence cost $2 one way. The first and last buttresses (adjacent to the wing wall abutments) are half the width of all other buttresses. The wing wall abutments are 25' wide where they meet the bridge; they increase in width and decrease in height as they as they spread out. They were built by William Otis using his first steam shovel. The bridge was "substantially complete" in June 1835 from various accounts of horse-drawn cars passing over it during that time. The bridge was built before the advent of construction safety equipment such as hard hats and fall arrest devices. Surprisingly, no deaths were recorded during the construction, but deaths have occurred at the bridge since completion; mainly from people crossing the bridge while trains passed in opposite directions. Charlie, the old white horse who had hauled the empty railcars back to Sharon, Massachusetts (4 miles), was placed upon the flat car and hauled across the viaduct by the workers, thus becoming the first "passenger" to cross the structure. Aside from seasonal vegetation control and occasional graffiti removal, the bridge requires no maintenance other than periodic bridge inspections from Amtrak. Foundation stone The foundation stone was laid on Sunday, April 20, 1834 with a Masonic Builders' rites ceremony to give the structure a "soul" and ensure its stability. This day may have been chosen to coincide with Paul Revere's Copper Mill founding in 1801 or the election of Jacques de Molay, the last Grand Master of the Knights Templar in 1292 A.D. The majority of the B&P's Board of Directors were Freemasons, including President Thomas B. Wales and Joseph W. Revere. President Wales was very involved in Freemasonry and gave three of his clipper ships Masonic names: Morning Star, Hesperus (Evening Star) and Templar. According to Masonic tradition, foundation stones are located in the northeast corner of structures with inscriptions such as the Masonic emblem ( square and compasses) and the date; they also contain time capsules. Freemasons use Fibonacci numbers in their structures, and there are examples of these " golden ratio" numbers in the Canton Viaduct:
  • The inscription on the back of the Cornerstone is recessed into an elongated octagon.
  • The original roadway portal was built through the eighth cavity from the south end and the concrete roadway portal was built through the thirteenth cavity from the north end.
  • The rise of the original roadway portal is 8 rows and the rise of each deck arch is 3 rows.
  • There are 5 voussoirs in each arch row (depth) of the original roadway portal and river portals.
  • There are 21 deck arches on each side of the bridge and 21 voussoirs in each deck arch.
  • There are 21 cavities in the bridge.
  • There are 13 voussoirs in each river portal.
  • There are 3 rows of stones in the Canton Viaduct monumnet, the bottom and middle rows have 8 stones each.
Cornerstone Canton Viaduct Cornerstone back inscription reads: FOUNDATION STONE LAID APRIL 20. 1834. The Operative or Craft Freemasons' calendar year was 5834 A.L. ( Anno Lucis - in the Year of Light) The Canton Viaduct Cornerstone was originally laid in the west parapet, south end. Select this image twice to see the latest version due to thumbnails and images not updating. Operative Freemasons laid the Cornerstone in the south end of the west parapet. According to Masonic tradition this location was selected due to it being the farthest distance from the foundation stone located in the northeast corner. This stone is sometimes referred to as the "Dedication Stone" and it was the last stone to be laid in the bridge. There are no Mason's marks on the front, back or sides of the Cornerstone but there may be some on the other surfaces. The Cornerstone is actually two stones now held together with two iron straps on each side. The overall dimensions are approximatrely 60" long x 36" high x 18" wide (golden ratio), and it weighs approximately 3,780 lbs. Due to its breaking in 1860, the Cornerstone is about 1" shorter today than its original height. The damage obscured two directors' names, W. W. Woolsey and P. T. Jackson. Woolsey was also a Director of the Boston & Providence Railroad & Transportation Co. ( B&P RR&T Co.) in Rhode Island (incorporated May 10, 1834) which owned the Rhode Island portion of the Boston and Providence rail line. The B&P RR&T Co. merged with the B&P on June 1, 1853.

Railroad track
During the 1993 deck renovation, two 18" deep troughs were discovered recessed into the granite capstones running the entire length of the viaduct and spaced at standard gauge width (56-1/2"). The troughs contained baulks or longitudinal sleepers and were part of the original construction. The baulks supported the rails with transoms between to maintain the gauge. A 1910 photo taken atop the viaduct shows dirt between the cross ties and tracks, so this material may have been used before traditional gravel ballast. Baulks were used to support strap rails or bridge rail. These early rails would have been replaced with flanged T-rails by 1840. These photos show baulks at Canton Junction in 1871. An 1829 report from the Massachusetts Board of Directors of Internal Improvements describes how the railroad from Boston to Providence was to be built. The report states, "It consists of one pair of tracks composed of long blocks of granite, about one foot square, resting upon a foundation wall extending to the depth of 2-1/2' below the surface of the ground, and 2' wide at the bottom". The report also calls for using horse drawn wagons and carriages at 3 MPH on the rail line, not steam locomotives.

Sequence
The Canton Viaduct was constructed in the following sequence:
  • Design and specifications
  • Site preparation, mobilization, surveying, excavation, timber sheet piling and cofferdams
  • Wing wall abutments - foundations and walls (Dodd & Baldwin and Otis)
  • Temporary train platforms and embankment staircases at abutments (B&P)
  • Bridge (Dodd & Baldwin):
    • Foundations - the Foundation Stone was the first stone to be laid on April 20, 1834 (northeast corner) with Masonic Builders' rites ceremony
    • Continuous walls, portals and buttresses
    • Cavity slabs
    • Deck slabs (with longitudinal troughs) and coping
    • Deck arches
    • Spandrels
    • Parapets - the Cornerstone was the final stone to be laid laid at the southwest end with Masonic ceremony
  • Track installation (Otis) - baulks and transoms, rail and ballast - the first "passenger" was Charlie, the workhorse
  • Site clean up and demobilization
  • Opening ceremony - July 28, 1835. The first train, "Whistler" passed over the Canton Viaduct at approximately 5:00 PM local solar time.


Waterway
A west side view of the Canton Viaduct with its waterfall in the foreground. Spillway Dam at Neponset St. - a.k.a. Canton Viaduct Falls impounds Mill Pond. It is a weir or low head dam that is owned by the MBTA. The 16' high by 90' long granite dam was built in 1900 and currently (2009) averages 78 cubic feet/second annual discharge. Water power was supplied to nearby businesses via water wheel from the canal starting at the waterfall's enclosed plunge pool and continuing about 200' under the Neponset St. bridge. There were also two channels located between the viaduct and the waterfall (one on each side) referred to as sluices, headraces and flumes in various maps. They were filled in sometime after 1937 (U.S. Army Corps of Engineers National Inventory of Dams No. MA03106).

Renovations and repairs
An east side view of the Canton Viaduct looking north shows some repairs in a 1906 postcard. Canton Viaduct's USNGS survey marker (Permanent ID: MY0489) is located on the west side of the concrete roadway portal, south end. A west side view looking south shows the viaduct's new cantilevered concrete deck and original iron fence from 1878 (restored). A south view from midway atop the Canton Viaduct. The new concrete deck can be seen with refurbished iron fence/rail, 4' walkways, catenary system, concrete ties, continuously welded rail and safety rails. The electrical substation is shown in the background off to the right. An artist's rendering of the 1941 proposed renovations (west side) with pedestrian portals, sidewalks and rebuilt roadway portal. This plan is on display in the Planning Board office in Canton's town hall (Memorial Hall). An artist's rendering of the 1995 proposed renovations (west side) with rebuilt roadway portal.
  • 1860 - 25 years after its construction, the increased traffic between Boston and Providence made the need for double tracking necessary. The roadbed was built wide enough to accommodate two sets of tracks, but only one set was originally installed. To accommodate the second track, the 3'-8" high x 18" wide granite parapets were removed. The Cornerstone was tossed off the viaduct and lay broken in a field for 18 years. The Cornerstone was the last known remnant of the parapets. It is not known if any stones fell into the river during this renovation. These stones may have been used in railroad projects or as mile markers or building foundations and walls in Canton. The granite parapets were replaced with a heavy cantilevered wooden fence fastened to transverse wooden floor beams. A hard pine curb was bolted at the edges of the deck to retain the new ballast. The deck troughs and baulks were abandoned at this time, and the troughs were filled in with stone. The timber approach structures would have been removed at this time to accommodate the double tracking. Although the bridge was able to accommodate two sets of tracks it was not the original design intent due to a single set of longitudinal troughs, the weak deck arches, and the narrow width of the deck - the outer rails of each set of tracks are above the deck's edge.
  • 1878 - The wooden fence was removed and replaced with a heavy cantilevered iron fence (of silimar design) from the Edgemoor Iron Company for $12,000. The new fence also used transverse floor beams (but made from iron) and was built to carry an 18" cantilevered footwalk that was never installed. The ends of the fence were flared (over the abutments) to guide trains onto the bridge if they derailed before reaching it. The Cornerstone was repaired by squaring off the broken stones and connecting them with two iron straps on each side. It was then raised to the top of the viaduct at the opposite (north) end facing East.
  • 1887 - Safety tracks were placed on the viaduct on April 15 to prevent a derailed train from hitting a passing train and/or falling off the bridge. The addition of the safety tracks was in response to the recent disasters at White River Bridge and Bussey Bridge. Many guard rail configurations have been used on the viaduct over the years.
  • 1897 - This photo shows the Mill Pond water level lowered to expose the bridge foundations for workers to make repairs. Another photo shows missing foundation stones that were replaced. All joints were filled with waterproof cement.
  • 1906 - Heavy timbers support a work platform in this post card dated October 15. Deck arch 13E is being repaired and suggests the deck arches were not strong enough to handle the ever-increasing loads or were deteriorating. This is the same arch that would later be opened to allow a second roadway passage in 1953.
  • 1909 - A stone in deck arch 10E dropped out of place and the arch was badly cracked; stonemasons began repairing it on Sunday, December 19. An article titled, "More Trouble with the Viaduct at Canton Junction" in the December 24 edition of the Canton Journal describes this as the second arch to have given way within a month.
  • 1910 - Reinforced concrete arches (42 total, 21 on each side) were added under each deck arch. The repairs took almost 2-1/2 years to complete. A report from this year describes the first known interior inspection.
  • 1912 - An interior inspection at arch 7 occurred in late October. A large stone was removed to allow access and three platforms with ladders were erected inside to facilitate inspection of the walls and underside of the deck. There were no broken or cracked stones and all joints were still full of good hard mortar. A photo from the inspection shows the formation of stalactites under the deck indicating water penetration which may have caused the deck arch problems from freeze/thaw cycles resulting in frost disintegration.
  • 1914 - Four wooden "jump-out" platforms (approximately 6' long x 4' deep) were attached to the iron fence supports for people to seek refuge upon when trains passed. The platforms were staggered every 154' and cantilevered over the deck arches (mid-span) 5W, 9E, 13W and 17E. The jump-outs were installed after the death of Canton Junction section foreman, Wilbert H. Jerauld who was on the viaduct when two trains converged and was unable to escape.
  • 1939 - During World War II guard houses were built at each end of the Canton Viaduct to protect the bridge from sabotage.
  • 1953 - 118 years after the Canton Viaduct's construction, a concrete roadway portal was cut adjacent to the original roadway portal in arch 13 to accommodate northbound traffic on Neponset Street. The $40,000 renovation took place in March and the cost was split by the town of Canton and the New York, New Haven and Hartford Railroad Co. This roadway portal is much smaller due to its segmental arch design and shorter width between buttresses. The cavity at arch 13 and foundations would have been inspected at this time.
  • 1963 - After years of Canton River flooding, the Army Corps of Engineers built the Canton Local Protection Project. The project's main purpose was to protect businesses along the river and prevent scouring of the viaduct's foundations during flood season and hurricanes as seen here during the Long Island Express hurricane of 1938.
  • 1965 - A USCGS benchmark (F31) was placed on the west side of the concrete roadway portal.
  • 1973 - Mason's marks on the bridge were cataloged and painted white by the Canton Historical Society in April. Painting of the Canton Viaduct's Mason's marks is known to have occurred one other time in the late 1800s.
  • 1995 - The MBTA and Amtrak rehabilitated the bridge for high-speed Acela Express train service. The main objectives of this $10 Million dollar project were to widen (13' track centers), strengthen and lengthen the bridge with a new cantilevered, precast, prestressed concrete deck, replace the concrete deck arches and institute electrification via catenary lines. Voltage for the 25 kV AC lines is provided by the electrical substation at the south end of the bridge. The original iron fence was also removed, refurbished and attached to the new deck. The new deck was 8' wider, with 4' walkways on each side that eliminated the need for the jump-out platforms. The concrete roadway portal was refinished and the USCGS benchmark was replaced.
Project challenges - It was necessary to maintain the historic fabric of the structure so all work was consistent with the Secretary of the Interior's Standards for Treatment of Historic Structures. The viaduct is located within Massachusetts DCR's Fowl Meadow and Ponkapoag Bog ACEC (Map Tile #7g) so protecting endangered species in the nearby wildlife refuge presented a challenge. Working in and over the Canton River required extensive permitting and close monitoring by environmental groups. The project was also located in a designated National Environmental Study Area. An excerpt from the September 1998 Railway Track & Structures article reads, "It was initially believed that the top of the viaduct was composed of solid granite blocks (originally carrying a single track). After the track and ballast were removed from the structure, troughs were discovered recessed into the granite capstones. The 18" deep troughs ran the entire length of the viaduct and were spaced approximately 56-1/2" apart (standard railroad gauge). In some locations, the trough contained a solid piece of oak, including some abandoned spikes. It is believed the troughs held wooden sleepers for the original single track railroad. These loose materials were removed from the deck, and lean concrete was placed to fill the voids. Archival photographs of the sleepers were taken and their remnants will be turned over to the local historical commission. At the approaches to the viaduct, a series of granite walls were uncovered running perpendicular to the tracks. These walls were approximately 7' on center, and it was thought that they might have carried a timber approach structure. The locations of the walls conflicted with new abutments for the PPC beams, and they made it difficult to install sheet piling for the contractor's support of excavation system. The walls were left in place undisturbed beneath the new track structure. HDR, Inc. redesigned the abutments to minimize their depths, eliminate the conflicts and reduce the loading of the temporary support of excavation system." When the railroad was complete except for the viaduct, trains ran to the bridge abutments where passengers would exit and descend the embankment. Passengers crossed the river on a hand-operated cable ferry, boarded horse drawn carriages on a temporary wagonway to cross the valley, then ascended the embankment to board a waiting train at the opposite abutment. The parallel walls at the abutments are believed to have supported the temporary (covered) train platforms to which wooden staircases were attached. These wooden staircases led from the train platforms to stone abutment staircases (with railings) for passengers to descended to the valley floor. A photo from 1871 may have captured one of those walls (bottom left), at the north end, west side of the viaduct. The parallel walls may have also served as foundations for the guard houses during World War II. Many capstones were discarded during the deck replacement project; they were placed in the field behind the viaduct. Some Canton residents recovered smaller stones from the massive pile before it was hauled off to an unknown destination. Portland Cement Association's Historic Canton Viaduct case study has more project details. Three interior inspections were performed in the winter by two structural engineers using rock climbing equipment to scale the interior walls. The inspectors noticed small, insignificant cracks in the walls and larger cracks in the deck stones that eventually lead to the deck being replaced. The stones of the viaduct were placed in such a way as to allow interior access at just three locations. Between the walls occasional tie stones connect the walls together. Some tie stones have large, loose stones placed on them to support work planks. The local film crew noticed rock crystal formation taking place, associated with the moist air inside and a rotting wooden platform. They also noticed some thin wood or iron pieces connecting the walls. It is unknown if these iron pieces or the platforms were used during construction or inspection. Stone stiles protrude into the airspace but do not reach the opposite side. The stiles were used to support work planks instead of traditional scaffolding due to the narrow space between the walls. [

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