Building the World Beneath Our Feet: Tunnel Construction Explained | The B1M

From subterranean roadways to the network of tubes that make up many of the world’s great mass transit systems and.

From subterranean roadways to the network
of tubes that make up many of the world’s great mass transit systems and the means by
which we move waste away from urban areas, tunnels are among the most critical pieces
of infrastructure that keep our cities moving. However, unlike above-ground infrastructure
which becomes a visual part of any city upon its completion, the scale, engineering complexities
and methods required to construct and operate our tunnels goes largely unnoticed by the
millions of people who use them every day. From digging in the dark to ensuring safety,
minimising disruption and bringing fresh air underground – these are the critical challenges
that must be overcome to make our world’s tunnels a reality. The methods used to build the majority of
today’s tunnels mean that, aside from a number of scattered access sites across their
routes, the work to form these structures goes largely unnoticed by the population. By contrast, the earliest tunnelling method
– known as cut and cover – was one of the most disruptive processes a city had to
endure to construct vital below ground infrastructure. With this method, engineers would first dig
a trench then lay bricks to form the tunnel walls before backfilling the excavation and
reinstating the surface above. This approach required large stretches of
the streets above to be closed for extended periods, creating congestion. In some instances,
properties along the route had to be acquired before works could proceed. The cut and cover approach was used to construct
London’s Metropolitan Line, the world’s first underground railway route. The impact
of the works to form this line can still be seen today in the numerous sections of track
that have been left exposed where buildings were not reinstated on completion. Today, Tunnel Boring Machines or TBMs are
used to construct tunnels in urban areas, eliminating much of the disruption that tunnelling
schemes caused in the past. Operating on the same basic principles as
the “tunnelling shield” developed by Sir Marc Isambard Brunel during the construction
of the Thames Tunnel in the 19th century, TBMs are able to excavate material and line
the tunnels that they form in one a continuous process – increasing efficiency and greatly
improving safety. Due to their size – varying between 150
to 200 metres in length – TBMs need to be delivered to their entry sites in pieces
before being lowered into access shafts and assembled. While variations of TBMs exist for different
soil types, the key piece of machinery common to all systems is the forward-facing, rotating
head which is lined with a series of blades able to cut through all manner of rock and
clay. Spoil from the excavation is funnelled behind
the cutter head and transported back towards the tunnel entrance via conveyor belts. Much of the spoil from the construction of
London’s Crossrail – one of the world’s largest infrastructure projects – has been
transported to the Thames estuary and used to create a vast new wetlands sanctuary. As the TBM moves forward, precast concrete
shells are brought in to form the lining of the tunnel behind it, preventing the surrounding
earth from collapsing back into the void. Due to the costs and logistics associated
with removing them, many TBMs, like those used to construct the Channel Tunnel, are
simply driven off into the earth and left in place once they complete their work. However, in recent times – and with their
costs increasing – a number of schemes have removed their boring machines on completion,
ready for re-use on future projects. While the physical construction of tunnels
is a considerable engineering feat, the ongoing operation and management of these structures
can be just as challenging. Regardless of their use, monitoring tunnels
throughout their lifespan to ensure their ongoing safe operation is paramount. Ventilation is critical, particularly with
road tunnels where high levels of pollutants including carbon monoxide and nitrogen oxide
are continually discharged. Numerous methods are used to improve the quality
of air in tunnels. While some systems force clean air through these underground spaces,
others focus on the extraction of pollutants through ventilation ducts, which in turn draw
fresh air in. We’ve used SimScale to simulate how such
a system works the Central Artery / Tunnel Project in Boston – a scheme which re-routes
the central artery of Interstate 93 through the Thomas P. O’Neill Jr. Tunnel. With more than 150,000 users worldwide, SimScale
is an easy-to-use cloud-based engineering simulation platform that enables everyone
to create powerful, high-fidelity simulations in a web browser. The platform can be tried for free through
the Community account, which gives access to thousands of public simulations to promote
knowledge sharing and to crowdsource advice. The ventilation techniques used in many tunnels
work in tandem with fire suppression systems to clear smoke in the event of a fire. Within road tunnels, extensive traffic management
and signalling systems are in place to reduce the risk of accidents between vehicles, which
could bring operations to a standstill in a considerably confined space. For motor vehicles, electronic displays provide
up to date information to drivers on which lanes are in use and alerting drivers to obstacles
ahead. It is also typically forbidden to change lanes
while travelling through tunnels to minimise the risk of incidents between vehicles. Many road tunnels also feature traffic control
systems outside of their entrances to prevent vehicles sitting stationery in congestion
once inside. In the case of metro tunnels, sensors on trains
and signals through the length of a tunnel’s route alert drivers to the status of other
trains ahead allowing them to remain at a platform in the event of an incident. In the unlikely event that these systems are
unable to prevent an accident within the tunnel, emergency systems alert drivers and passengers
to abandon their vehicles and proceed to the nearest refuge or escape point. In addition, many modern tunnels are now built-in
pairs, with traffic travelling in a single direction to further reduce the risk of a
head-on collision. This approach allows passengers to pass through
to the safety of the alternate tunnel in the event of an emergency. Though they often go unnoticed, tunnels are,
in fact, the arteries that power our cities. Passing beneath our feet and transporting
millions of people every day, these critical pieces of infrastructure are truly in a world
of their own. If you enjoyed this video and would like to get more from the definitive video channel for construction Subscribe to The B1M.

80 thoughts on “Building the World Beneath Our Feet: Tunnel Construction Explained | The B1M”

  1. Thanks to The B1M videos, I always see the end of the tunnel when it comes to expanding my knowledge on amazing constructions. Thank you.

  2. 1:10 Just like the railwaytunnel project #Västlänken in Gothenburgh, Sweden (Pewdiepies hometown btw). Since most of it is soft clay, much has to be dug up. It would be really cool if you did a deep analysis on that project, the tech, the controversies etc. If you want a benchmark on how to not handle public opinion, #Västlänken it is. Estimated cost: 4 Billion Euros. Population: Only 800 000. It's a political and PR nightmare.

  3. How can you make a video on the state of the art of tunneling and not once mention the Boring Company? I would think that bringing tunneling costs down would be a major point of interest.

  4. If, like me, you geek out on this sort of thing, you might well enjoy a behind-the-scenes tour of the Queensway Tunnel in Liverpool:

  5. The presentation of information on this channel is extremely professional. This is National Geographic worthy in my opinion. You guys are seriously on another level.

  6. When one direction of the Eisenhower Tunnel is closed, and both directions of traffic have to use the same tunnel, it can be unnerving.

  7. Homeless. Wish I 'could' "subscribe". I really like these. Phoenix put in light rail. I wish they would've done this. Maybe they didn't because of the ancient soil types. Or maybe costs. Or because the nature of Phoenix is mostly leisure/suburban/retirement and tunnels would not actually be needed in 'this' time. I think not, though. Accidents. Congestion. Quality of life in dividing neighborhoods and response time of emergency services. Oh well. Who am I to care?

  8. Great video B1M always keeping me interested 🙂

    I remember this being an issue in the Netherlands with a tunnel they were drilling for the North-South line in Amsterdam.
    The TBM's would be used but because they soil on which Amsterdam was built (swamp lands) caused issues with the water levels when soil and moisture would be removed. Which caused houses to sink. Eventually it was completed and they found a way to work around that issue but it was still a irritating factor for the inhabitants.
    Just a fun did you know!

  9. Another superbly processed video B1M. I am always pleased to see something from our capital city, such as this time the metro station Smíchovské nádraží in Prague at 0:17, or the Blanka tunnel at 5:50 ?

    way to set off future archaelogy, guys ^^
    I didn't know that and didn't even consider it possible !!!

  11. Good one! Tunnels are underrated section of infrastructure.
    B1M there is something about your narration which makes your videos so interesting.
    I knew how TBM works but the way you explained it was amazing!
    As always keep up the good work.

  12. I've been looking forward to getting home all day just because its Wednesday. Now gonna relax and enjoy the evening away with my favorite channel

  13. I like your videos a lot, I would like to see how the Singapore infrastructure looks, in especial the public transport system and how it is vital for the citizens life

  14. It's great to see you guys cover such an important topic. Even amongst engineers, tunnel design and construction still remains a largely specialized and poorly understood expertise. There are many different types of tunnels, not only c&c and tbm, but it would be impossible to cover everything.

  15. This channel is a fav.? Only thing I don't like (not B1Ms fault) is how few females comment. ? Sometimes I feel like the only chick that watches this stuff. But how can you not be fascinated?! – It's awesome!

  16. You should do a video about the Noord-Zuidlijn metro in Amsterdam! Its a metro line in clay ground. Its a hard job making sure the tunnel doesn’t collapse

  17. I'm currently struggling trying to find my career path. I just finished my BCOM Finance Specialist Degree but I don't think I would enjoy working at a bank or in corporate finance. However, I'm really fascinated by construction/architecture/real estate. I watch every B1M video and my dream job when I was younger was to be an architect. I don't think it's feasible for me to go back to school so I won't be able to pursue another undergrad degree. Can anyone recommend a type of job where I can work in this industry whilst using my degree that I earned?

    So far I thought of working in Commercial Real Estate Investing or Development.

    I was hoping some industry experts in here may have some insightful experience to offer. Any other ideas are welcome 🙂

  18. I would love to see a video about the massive dams the Netherlands has build in recent years to claim more land mass and prevent the country from flooding. These are such massive structures!

  19. Always been fascinated by tunnels. Especially from growing up in Western Norway were there are a lot of groundbreaking tunnels and tunnelprojects.

  20. Firstly, let me congratulate you for this amazing content you post weekly.
    Secondly, a question: what do you suggest is better for a city, an underground metro or above ground one?

  21. It would be great if a feature was done on immersed tunnels and their cost per km and minimum land required on each side of say a 10km twin road and rail immersed tunnel traversing a wide river or sea like the Fehmarn Belt Fixed Link

  22. Great video, but what I've always wondered, though never quite enough to google it, is how do France and England start tunnelling at opposite ends and guarantee that they meet in the middle and at the right depth?

  23. Too short if you ask me. Could go a little deeper into the matter and add some fun facts (longest tunnel, deepest tunnel, most complex tunnel to construct etc.). Furthermore, keep up the good work guys!

  24. I've been on trains through the Channel Tunnel. It feels like any other train running in a tunnel, except that it doesn't stop and you have no idea how far under the surface you are.

  25. I was surprised when you said they leave their TBM The Underground when they finish the project I thought they always took it out on every project when the first TBM was invented can you talk about any abandoned TBM that are still Underground

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