Beneath the iconic London landmarks – the Shard, London Eye and Big Ben – lies the world’s first subway system to have been built.
Construction of the London Underground began in 1854, and after almost a decade of development, it officially opened to the public on January 10th, 1863.
The initial line, known as the Metropolitan railway, was the worlds first ever subterranean railway and ran for a length of 6km between Paddington and Farringdon.
Building the railway came with many challenges, particularly in deciding which tunnelling technique would be the most effective.
At the time, underground construction was a completely new concept, requiring engineers to pioneer innovative solutions to get around the complex task of digging through London’s often difficult geology.
The cut and cover technique
This method used for the first few lines for shallower tunnels.
The cut and cover method involved digging a trench along the proposed rail route, laying tracks at the bottom and then covering the trench again once the tracks were in place.
This method was relatively cost effective and simple however had significant drawbacks at the time.
It caused major disruption to the surface of streets, leading to long periods of construction noise, traffic delays and displacement of local businesses. Additionally, it was also only suitable for depths between 10 and 12 metres.
Despite these limitations, the technique was suitable for the first stretch of the Metropolitan railway being relatively shallow.
Stations which remain standing today and used the cut and cover technique include Euston, South Kensington and Paddington (one of the oldest stations on the underground).
Expanding the underground
As the London underground expanded, deeper tunnels were required, meaning the cut and cover method was no longer practical.
To combat this dilemma a tunnel boring shield was developed by Marc Isambard Brunel.
It was a large cylindrical frame that supported the tunnel walls as they were being extended, this method enabled the construction of tunnels up to depths of 40 metres
The use of this shield meant; workers could create tunnels deeper in the soil (e.g. clay) without the risk of tunnel collapse.
Once the soil was excavated, they were reinforced by brick or cast-iron linings creating a stable structure.
Overcoming geological challenges
The geology of London posed additional challenges as some of London’s soils were waterlogged and had high water tables.
To address this, pumping stations were installed to remove excess groundwater as well as grouting (a mortar or paste for filling crevices), this reduced the risk of flooding.
By 1863, engineers had successfully created a functioning underground rail system carrying 38,000 passengers on its opening day.
Today, the underground systems transports more than 1.3 billion passengers annually and has inspired the development of underground systems all across the globe.
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