There are many different tunnels. I will tell about four: the Thames Tunnel, the Frejus Tunnel, the Seikan Tunnel, and the Hoosac Tunnel.
In 1823 people were planning to build a tunnel under the Thames river in England. Then a man with the last name of Brunel made a design for a tunnel under the Thames river and a special tunnel boreing tool he called the Brunel sheild. The construction started slow. They made brick floors and iron rings to hold it together. Then one day it flooded. No one drowned, but workers were getting sick because all of Londons waste was dumped into the Thames river. When it flooded again six people drowned. Brunel became very sick so his son had to take over. They had no more money so the construction was stopped for seven years. During that time young Brunel was building rail tunnels across the country. Finally the government gave Brunel a loan. The construction started again. Around nine hundred people were touring every week. Finally they finished! The Thames Tunnel became the first round top tunnel ever. When the Queen came to the tunnel the person selling handkerchiefs laid them on the floor and later sold them charging double the price saying the Queen had touched them.
In the 1800s people in Europe needed a way to get trains across the Alps. So in 1845 King Carlo Alberta of Sardinia, started planning a tunnel under Mount Frejus. In 1849 King Alberta died so his son, Victor Emmanuel II continued his idea. He wanted to use the most modern building systems. In 1857 Emmanuel started the construction. Compressed air was used instead of steam to bore it. Hand drills were used until large equipment could be shipped in. Once large equipment was available, construction on the tunnel went twice as fast. An eight drill carriage jumbo was used. There were no problems during the construction of the Frejus Tunnel. Unlike the Thames Tunnel that had a lot of problems. The French soon took over the opposite side of Mount Frejus. They bored from their side and paid for their own expenses. This made the tunnels construction go even faster. Then in 1870 the tunnel was finished. Now trains can go under the Mount Frejus.
The Seikan tunnel is the longest rail tunnel in the world. It stretches 55 kilometers.This tunnel connects Honshu and Hokkado, Japan. One fourth of Japans working population built the Seikan Tunnel. The lowest point in the Seikan tunnel is 100 meters below sea level.The Seikan tunnel is an engineering masterpiece.
The Hoosac Tunnel was built under Mt. Hoosac. Geologists and engineers estimated the tunnel would cost $1,948,557 and take 1,550 days to build. American engineers studied the tunneling techniques used during the construction of the Frejus Tunnel. The same tunneling techniques were used to build the Hoosac tunnel as the Frejus Tunnel. The construction started in 1851. To build the Hoosac tunnel engineers used an early version of the TBM. The tunnel was completed in 1873 and cost $17,000,000. The first estimation was totally off. The Hoosac Tunnel was an amazing tunnel and one of the few tunnels that was built without any major problems.