Sunday, November 12, 2017

CN/GTW+GTR St. Clair Tunnels

(Bridge HunterHAERPort Huron Portals SatelliteSarnia Portals Satellite)

(Whoops, another duplicate. See Feb 3, 2019 for my second crack at these tunnels.
CN derailed 40 cars in the tunnel on June 28, 2019.)

"Built 1888-1891; Electrified 1907-1908; Electrification removed 1958: Tube sealed 1994" [Bridge Hunter]

(new window)  This video has a lot of history of the GTW before it gets to the tunnels @ 12:00. By the 1870s it went from Portland, ME to Chicago and was the longest railroad in the world under one ownership. [@8:45]

The Grand Trunk Railway (GTR) built a railroad from Portland, Maine to Sarnia, ON, which is across the St. Clair River from Port Huron, MI. "In 1880, the Canadian interests consolidated four railroads as the Chicago & Lake Huron Railroad which ran between Port Huron and Valparasio, IN, where it connected to the Pittsburgh, Fort Wayne and Chicago Railroad to gain access to Chicago." [IndustrialHistory] What became the GTW continued to build into Chicago so that it could use Dearborn Station when it was ready in 1885. The GTR and GTW then used railroad ferries to carry freight cars across the St. Clair River between the GTR and GTW.

National Historic Landmark Nomination, p24, from Scientific American, September 13, 1890.  
The GTR knew the ferry service would be a significant bottleneck so they built a tunnel. It is relatively easy to blast a tunnel through a mountain made of hard rock. In fact, the harder the rock the better because it reduces the chance of caveins and hitting water aquifers. But digging a tunnel through the muck under a river (in this case soft blue clay) was impossible until Marc Brunnel invented the tunnelling shield to dig a tunnel under the Thames in London. Work on the Thames Tunnel started in 1825, and it was opened in 1843.
In October 1884, the Grand Trunk chartered the St. Clair Frontier Tunnel Company as a Canadian corporation to construct the tunnel and Tyler put the Canadian engineer Joseph Hobson in charge of the project. The Grand Trunk also chartered the Port Huron Railroad Tunnel Company in Michigan in October 1886, and in November 1886, the railroad merged the twin companies to form the St. Clair Tunnel Company, which built the tunnel and operated it until 1958. 
Hobson made two failed attempts to drive the tunnel by traditional means, in December 1886 - July 1887 and in April - July 1888. After completing a detailed set of borings along the tunnel route in May - July 1888, Hobson decided to design a tunneling shield and to start tunneling from a point nearly one-third of a mile from the riverbank. He excavated great open cuts on both sides of the St. Clair River starting in January 1889 and began shield tunneling on the U.S. side in July 1889 and on the Canadian side in September 1889. Hobson introduced compressed air between March and May 1890. The two shields met on 30 August. 1890 and the St. Clair Tunnel officially opened on 19 September 1891. Hobson had successfully combined three innovative techniques for the first time in the construction of a large-size subaqueous tunnel--the tunneling shield, a cast iron tunnel lining, and the use of a compressed air work environment. 
This tunnel has undergone only minor changes since its opening. Following the deaths of ten men by asphyxiation between January 1892 and October 1904, the Grand Trunk electrified the tunnel, a project it completed in February 1908. The railroad lowered the tracks in 1949 to allow taller freight- cars to use the tunnel . Diesel locomotives went into service in September 1958 and the railroad installed new ventilation equipment to handle the diesel fumes. 
[HAER MI-67 from mi0525, p3]
This was the first tunnel built under a river that was large enough to be used by a railroad. The tunneling shield is an update of that used by Brunell by using iron and instead of bricks to line the tunnel and by using hydraulic instead of screw jacks between the lining and shield to force the 80-ton shield forward into the muck. Using iron lining segments instead of bricks immediately provided a structurally sound surface for the jacks because you did not have to wait for the mortar to cure [National Historic Landmark Nomination (NHLN), p11]. You can tell that the 1880s was in the transition period from iron to steel because the lining segments were made with cast iron whereas the shield was fabricated from steel.

The Scientific American illustration below calls it a Beach shield, but it is more similar to Greathead's shield, but twice the size. A set of 24 hydraulic rams powered by water that could be pumped with as much as 5,000 psi could produce a total pushing force of 3,000 tons. The greatest force required was 960 tons. [HAER MI-67, pp13-15] With the counterweighted lever we see in the illustration to place the half-ton lining segments into place, it struck me how similar this boring and lining technology is to a modern Tunnel Boring Machine. Todays TBM uses precast concrete slabs instead of cast iron ring segments, a conveyour instead of mule drawn wagons, and a rotating cutting wheel instead of men digging with tools. Note I said digging tools instead of shovels. "In the early stages of excavating, one digger, John Ordowski of Port Huron, invented a tool that replaced the ordinary shovels used to dig the clay. The knife-like device, with handles for two men, would 'cut.' a slice of clay roughly a yard long and several inches thick at a time. Only two or three men of the crew of 22 diggers in the shield removed the clay from the shield proper." The remaining men did the various steps needed to haul away and dispose of the clay. [HAER MI-67, p15] "It took about 45 minutes to erect a single ring in place." [NHLN, p13]

National Historic Landmark Nomination, p23
Two shields were used so that the tunnel could be dug from both ends at the same time. When a tunnel got close to the edge of the river, they built a bulkhead with airlocks across the tunnel and pumped compressed air into the river side at up to twice atmospheric pressure (30psi). If they dug into a water or quicksand pocket, the compressed air kept it from flooding the digging chamber and work could continue. This technique was pioneered in pneumanic cassions used to dig deep holes under rivers to reach bedrock to build piers for big bridges. A risk with using compressed air is that if they dig into a weak spot in the muck, the air might blow out and up into the river. A blowout can cause a flood and drowning.

Mammals have trouble working with higher air pressures. They had to switch to mules because the horses could not cope with the higher pressure. Since the tunnel stayed close to the bottom of the river, rather than going deep to reach bedrock, I didn't think they would have a problem with the bends. Bends are caused by bubbles of nitrogen forming in the bloodstream if the air pressure is reduced too quickly. Evidently they also thought they were shallow enough that they did not have to worry about the bends. But they did:
Originally, the air locks had a single 4-inch globe valve to equalise the air pressures but this allowed too rapid decompression and caused many cases of the "bends," more commonly called "the benders" by the men, because their knees would buckle and they would bend over in pain. The men would frequently bleed through the nose, mouth, and ears. Three men died of the "bends" during the tunnel project and scores suffered from the disease. In time, they substituted a 1 1/2-inch valve in the air lock, slowing the rate of decompression. Even with the smaller valve, men would pass through the air lock in about 2 minutes. Engineering News believed that extending the decompression time to 5 minutes would eliminate most cases of the "bends," but conceded that this might slow the pace of work. The number of workers in the compressed air zone at any given time was between 50 and 75. [HAER MI-67, p23]
A ventilation system was installed to mitigate the risk when natural gas pockets were breached. They used electric lights so they did not have the risk of burning something for lighting.

By the late 1960s, the tunnel was no longer able to handle the taller freight cars used for traffic related to the automobile industry, especially tri-level auto carriers and special 85-foot long automobile parts cars. In March 1971, Canadian National had to reintroduce railroad car ferry service between Port Huron and Sarnia using the tug Phyllis Yorke pushing the barge St. Clair. They added a second tug and barge a few years later to provide enough capacity to handle the larger volumes of traffic.  [HAER MI-67, p35]
The growing popularity of "double stack" cars made the 19' 10" tunnel even more obsolete.
By the beginning of the 1990s, GTW decided to build a 31' diameter tunnel just north of the old tunnel. In the following satellite images you can see the old and new portals.

3D Satellite, looking east at the Port Huron (American) portal
Satellite, Sarnia (Canadian) portal 
Joe Dockrill shared
big project in 1994, CN had thier own tunnel boring machine for doublestacks

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