Here is some fancy equipment that can bore tunnels like no John Henry's hammer ever could:
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What's interesting about the tunnel is technology really hasn't changed since the 1850s. We use modern methods, but the blast patterns set up by the pyro-tech engineers are the same, and while we use a GPS and satellite for sighting to keep the tunnel on track, the engineers used prisms, plumb lines, sighting towers, and vertical shafts.
In the late 1840s, the Fitchburg Railroad wanted to build its own route west from Fitchburg, MA to Troy, NY. Like most railroad companies, they applied to the state for a charter, created a company, and set about raising stock. This company, the Fitchburg & Troy Railroad, then set out to build their route but ran into a couple of snags, to put it mildly.
While they had to go ahead from the state of Mass, their largest competitor the Boston and Albany Railroad controlled then only route west through the Hoosac Mountains to New York, and did a bit of influencing that made building the F&T difficult.
When the private money ran out, the state took over and doled out funds based on specific goals, except they held back funds because they goals weren't met and made the goals way too lofty with no money to complete them. Hermann Haupt, the engineer hired to build the Pennsylvania Railroad, went bankrupt by putting in his own money to pay the workers to keep the project going. In other words, nothing has changed!
With that in mind, this railroad was one of firsts:
This was Massachusetts's first Big Dig Project and cost the state $25,000,000 and took 25 years to build the 4.75-mile tunnel through the Hoosac Mountains.
This was once the longest tunnel in the Western Hemisphere and longest in North America, and held that title until the long tunnels were built in the Rockies during the early 1910s. The state ended up owning the project due to financially collapsing the construction due to finagling by the Boston and Albany.
This was the first tunnel to utilize a tunnel boring machine.
It failed initially due to being too weak to drill through the extremely hard East Portal side of the Hoosac Mountains made of granite, quartzite, gneiss, schist, and feldspar. The initial test on the west side in North Adams was a success due to the softer rock. A later machine was brought in near the end to finish the job in the 1870s.
Surveyors used vertical shafts, and light towers.
Spaced out over the hills and mountains along the route. A plumb line with a prism would be dropped down the shaft that reflected light that was cast off of a tower on the top of the hills. This light was then used to point the direction where the navvies were to dig. When the tunnel was completed, they were off about 4-inches over the nearly 5-mile tunnel. Today, we use satellites and GPSs to guide the workers and machines.
The development of blasting patterns, tri-nitroglycerine, dynamite, and the use of electricity to blow stuff up.
Up until Dr. Mowbray came in to work on the tunnel, along with some engineering consultants from Toronto, the digging was slow. Workers were digging maybe a few yards a day using the very dangerous and very unpredictable black powder.
Dr. Mowbray, the famous explosives engineer, developed the blasting patterns to dig the tunnel quicker and easier. These are the same patterns used today for the same reason.
Rather than using black powder, they used nitroglycerine which is also very unstable but had more punch to it and extremely powerful when placed in the circular pattern still used today. This led to the development of tri-nitroglycerin in the early 1870s. One February morning, Dr. Mowbray was shuttling some jars of nitroglycerine over the mountain from the West Portal side where there's a large water supply, to the East Portal where the rock had to be dug.
Being a cold February morning, and most likely a slippery one at that, his horse went off the road. He thought then and there he was maimed or dead only to wake up with a few bruises instead! After that, he chilled down the nitroglycerine at the nitroglycerine plant on the West Portal side and shuttled it quickly east for use.
What to do about the summer? Once the tri-nitroglycerine melted, it became unstable again. Dr. Mowbray set about creating something that was stable during both summer and winter, and to light it all up "safely", electric blasting equipment was developed.
On a side note, the West portal was softer and made up of very soft, wet porridge stone. The stone is made up of mica and sand, and literally dissolves in water to form something that's the consistency of porridge. The engineers ended up using bricks to hold up the ceiling on the west end because of this due to the mushy porridge collapsing. As I said, the east side was literally rock solid and slow going.
The then double-track tunnel opened up in 1874 with much fanfare and close to 100 trains an hour passed through the tunnel in both directions. With the smoke so thick and dangerous, the tunnel was electrified in 1907 with the help of the New Haven Railroad, who was part owner of the Boston and Maine Railroad by this point. The electric motors hauled trains from Hoosac Tunnel Station through the tunnel to North Adams from 1907 until 1946. In 1946, the B&M ran its first diesels, a set of 4 EMD FTs, through the nearly 5-mile tunnel, thus ending the electric service then and there.
The tunnel is still in use today, but not at the frequency it saw in the early days. Today, there are about a dozen freights run on the jointly-owned Pan Am Southern route. PARS is jointly owned by Norfolk Southern and today CSX who inherited the route with their purchase of Pan Am Railways. CSX does not run the route and GWI, Berkshire Southern does on their behalf along with NS.
Here are some videos of the electrics taken during the heyday of the tunnel.
