The History of The London Underground


This episode of Real Engineering is brought to you by Skillshare, home to over 17,000 classes that could teach you a new life skill. The first 500 people to sign up with the link in the description will get a 2 month free trial. Few inventions have had as a revolutionary effect on her society as the advent of the steam engine. This machine allowed the automation of production, creating thousands of new jobs in our cities and drawing humans from our farmland existence to an ever more metropolitan life. The population of London doubled in the first half of the 19th century as people flooded from the countrysides in to London’s Kings Cross on the very engine that spurred the new trend of urbanization and industrialization. With few options for transport within the city beyond horse and carriage, these new city dwellers had little choice but to live in crowded slums near their places of work. Areas like Whitechapel and Spitalfields that were once home to the prosperous Victorians and French Huguenots became disease and crime infested homes to the working-class. These areas had one thing in common. They were within walking distance of Kings Cross, the supply line of the city’s new factory workers. London needed a new transport system to allow these workers to spread out and prevent overcrowding. But with little space above ground for an urban rail system, London city planners needed a novel approach and so the world’s first underground rail system was born. Our ancestors have probably been digging burrows and tunnels since they climbed down from the trees, but the earliest tunnels we know of existed as far back as 2000BC. Most tunnels were created for mining or military engineering, often through stable rock and over short distances. In fact, the word for “mining”
and “mine” (used for an explosive device) are closely linked for exactly this reason, as early tunnel technology was developed in order to approach fortification walls undetected to place an explosive charge. One of the primary reasons moats became popular was because ground water mixed with soft porous soil was one technical problem these early engineers had no solution for. Constructing tunnels was and still is dangerous work. Tunneling accidents were common, whether it be from flooding, tunnel collapse due to inadequate reinforcements, or explosions. The fear of collapse was always on the mind of these workers who dug these tunnels with simple tools like pickaxes and shovels in dark, claustrophobic environments, despite the constant risk. Civil engineering made huge strides in tunnel building techniques over the course of the 19th century. Starting with the world’s first underground railways in London, but the development of the London Underground was made vastly easier, thanks to the London clay, which the city is built upon. Although the soil today makes it difficult to build skyscrapers, as it cannot support their weight, it is ideal for tunnelling, being soft yet relatively stable. London’s first underground railway line, the Metropolitan line, began in 1863 and was mostly built using the cut and cover technique. A trench would be dug, walls and a supporting roof structure built, and then buried again. A safer and easier tunneling technique, but it resulted in the demolition of streets or whole city blocks. Even today, the remnants of this construction technique can be found with hollow buildings hiding the scars of London’s past. The Metro in Paris was largely constructed this way, and in 1970s Amsterdam, the use of these cut and cover techniques led to the Newmarket riots and even an attempted bombing at one of the new metro stations. The new 3.5 kilometer line forced a destruction of numerous homes, in a time when Amsterdam was struggling with a housing crisis. The plans for a complete Amsterdam underground were abandoned as a result. No new subway line would be built through the city center until 2003, with the help of a tunnel boring machine
which began life in London in 1825. Marc Isambard Brunel together with his son, Isambard Kingdom Brunel invented a technique to make tunneling somewhat safer and less invasive – the tunneling shield. This shield was a scaffold-like wrought iron structure with 36 chambers, each containing a single workman. These chambers were further broken down by polling boards which were horizontal planks of wood that the workers removed individually to hew out the tunnel wall to a predetermined depth before replacing the board and moving on to the next section. Separating the tunnelling face like this compartmentalized the constant risk of tunnel collapse, reducing the chance of a small collapse in the face cascading and causing a total collapse, burying every worker in the area. Once each worker had finished their work, the entire shield would advance while bricklayers rushed to finish supporting brickwork behind the shield. This early concept laid the foundation for all future tunnel boring machines, but much was left to be improved. Construction of Brunel’s Thames tunnel was fraught with problems despite this new tool. Water constantly seeped into the tunnel which was a nuisance while pumps were operational, and a disaster when the pumps failed in the summer of 1826: resulting in the tunnel flooding up to 12 feet with polluted Thames river water. This, combined with poor ventilation, made working conditions horrendous. Temperatures rose and plunged with no warning, and workers complained of illness ranging from headaches and diarrhea to temporary blindness, and one worker died from his illness. This was just one of many problems that Brunel encountered and we would need an entire video to document it all, but the team persevered and 16 years later with the painfully slow progress of just four inches a day, the tunnel opened to pedestrian traffic in 1843. The project tested the technology of the time and provided vital lessons for future projects. In 1869, a second passage was dug under the Thames from Great Tower Hill to Pickle Herring Stairs. It was built with a much improved version of the tunnelling shield by Peter William Barlow. Barlow made one crucial change to the design: instead of a rectangular cross section, he made the shield circular, improving its ability to support the surrounding soil and the swelling of the Thames River above it. This passage under the Thames was fitted with a narrow gauge railway and a cable-hauled wooden carriage carried passengers back and forth. This proved to be uneconomic and the company went bankrupt within a year. The tunnel was then converted for pedestrian use and became known as the Tower Subway. It was relatively cheap to cross the Thames this way, however, when the toll-free Tower Bridge was opened, the subway’s income dropped and was sold in 1896. Currently, it’s in use as a utility tunnel for water mains. Barlow’s design was further improved upon by James Henry Greathead, when constructing the city and South London railway nowadays part of the northern line. Using compressed air tunnelling below the ground water table became safer, as the pressurized air prevented water inflow into the tunnel. Workmen would enter and exit the excavation through an airlock. This, together with a circular shield and cast iron rings to line the tunnel walls made for a much safer and efficient job. This is how many of the deep-level tube lines were built and travellers on the underground could still see the cast iron rings lining the tunnel walls in certain places. The circular shape of the tunnels this method created inspired the London Underground’s name – ‘The Tube’. To this day, most tunnelling shields are loosely based on the Greathead shield. Modern day tunnels like the Royal Oak to Farringdon tube line are built using TBMs or “tunnel boring machines”. And these long machines consists of several sections and essentially form an automated assembly line for tunnel boring. The front section of the machine is a modern version of the tunneling shield, however, nowadays it features a rotating cutter head. These rotating heads can be equipped with different tools depending on the type of soil. As the head rotates, the loosened soil enters the mixing chamber directly behind the cutters, where a screw conveyor transports the soil out of the cutter head and onto a conveyor belt. This conveyor belt then transports it out of the tunnel while the machine automatically installs reinforcements as it progresses. These new machines allowed the London Underground to expand even further with minimal disruption to life on the surface. With possible future improvements decreasing the cost and time needed through endeavors like Elon Musk’s boring company, our societies could be in for more radical change. With ever-growing city populations empowering people’s movement can and will increase our quality of life, just as these early engineers facilitated a radical societal change for the working class, in cities like London. You can create your own radical social change by learning a new life skill, and what better time of year to do with the New Year’s? So why not start your new year by signing up to Skillshare – home to over 17,000 classes
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