Ep 5. World's Longest Tunnel

The Impossible Engineering season 2 episode 5 takes viewers on a journey through the construction of the world's longest tunnel – the Gotthard Base Tunnel in Switzerland. The tunnel spans a staggering 35 miles and runs through the heart of the Swiss Alps, making it a true feat of engineering.

The episode starts with an overview of the history of the Gotthard Tunnel project, which dates back to the 1940s. The idea of a high-speed rail link through the Alps was first proposed in the 1960s, but it wasn't until the 1990s that serious planning and construction began.

Viewers get an up-close look at the complex tunnel-boring machines (TBM) used to excavate the tunnel. The TBMs are custom-built behemoths, each weighing up to 3,000 tons and measuring over 400 feet in length. They work round the clock, drilling through solid rock at a rate of up to 150 feet per day.

The episode also explores the various challenges the engineers faced during the construction process. One major obstacle was the high temperatures inside the tunnel, which reached up to 130°F due to the heat generated by the TBMs. The solution? A state-of-the-art cooling system that pumps cold water through the tunnel and keeps the temperature at a more reasonable 68°F.

Another major challenge was the geology of the Alps themselves. The tunnel had to pass through a variety of rock formations, including granite, gneiss, and schist. Each required different drilling techniques and equipment, which meant that the TBMs had to be constantly adapted and upgraded to meet the changing conditions.

As the episode progresses, viewers get a sense of just how massive the project was. Thousands of workers were involved in the construction of the tunnel, which took over a decade to complete. They had to navigate treacherous terrain, work in confined spaces, and deal with extreme temperatures and other hazards.

But despite the challenges, the Gotthard Base Tunnel was finally completed in 2016. It's now the longest railway tunnel in the world, reducing travel times between Zurich and Milan by up to an hour. And the engineers who worked on the project can rightfully claim to have accomplished one of the greatest feats of engineering in history.

Overall, the Impossible Engineering season 2 episode 5 is a captivating look at the construction of a true engineering marvel. It's a testament to human ingenuity and perseverance, and a reminder of the incredible things we can accomplish when we set our minds to it. Whether you're a fan of engineering, history, or just awe-inspiring feats of human achievement, this episode is not to be missed.