Episode Six: Going underground
How to Build a Railway is a twelve-part podcast series exploring the story behind the construction of the UK’s new high speed rail line.
The latest instalment of HS2’s podcast delves into the fascinating world of tunnelling. As Phase One of the railway winds its way from Birmingham to London, it passes through an ever-changing landscape. Shaped by towns, cities and countryside, HS2 has been designed to minimise the impact on communities and the environment.
This episode of How to build a railway, ‘Going underground’, explores one the most powerful tools in the project’s arsenal as we go underground to meet those who are calving the 64 miles of tunnels on the first phase of the project.
Featuring
- Martin Herrenknecht, Herrenknecht CEO
- Anders Danielsson, Skanska President and Global CEO
- Martyn Noak, HS2 Head of Tunnel Engineering
- Eddie Woods, HS2 Civil Engineering Support
- Daniel Worsley, SCS TBM Tunnelling Manager
- Michael Greiner, SCS Lead tunnel Manager
The episode kicks off with Martin Herrenknecht, CEO of world leading TBM manufacturer Herrenknecht. Martin shares an interesting career journey and how HS2 stacks up against other major projects.
We also hear from HS2’s own Martyn Noak, Head of Tunnel Engineering, and Eddie Woods, Civil Engineering Support, about the unique challenges of tunnelling under motorways, rivers and the Euston throat – already having the largest underground spaces created for transportation in Britain.
The episode also features tunnelling experts from main works contractor SCS, Daniel Worsley and Michael Greiner, as well as Anders Danielsson, Skanska President and Global CEO, who describes some of the key takeaways the HS2 project has already given to the industry worldwide.
Episode Six – Going Underground (transcript)
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Episode transcript
This is a transcript of episode six of HS2’s How to build a railway podcast, first published on 4 April 2023.
Fran Scott: Hello, I’m Fran Scott, and this is How to Build a Railway.
As High Speed 2 winds its 134-mile way from Birmingham to London, it passes through an ever-changing landscape. One that has been shaped by centuries of migration, settlement, growth and development. There are cities, towns, villages, and countryside all line the route, and all present their own set of challenges.
HS2 has been designed to minimise its impact on communities and the environment, both in the short term and in the long term. In this episode we are going to explore the most powerful tool in the project’s arsenal…
It is dirty and dangerous, and it is very expensive, but it’s incredibly exciting and important. Because it’s the only way a railway can pass through a town or an area of outstanding natural beauty without anyone knowing it is there.
In this episode we are going underground to meet the tunnellers.
1:23
Fran Scott: In 1812, the famous engineer Marc Brunel was puzzling over the problem of how to build a tunnel under the river Thames.
While he worked at the docks in Chatham, he became aware of the ‘shipworm’ for the first time… he wrote of the occasion to his granddaughter, Sophia.
1:51
James Chappelow (as Marc Brunel): “…I happened to see before me a piece of condemned timber, a portion of the keel of a ship, wherein the sea-worm had made many erosions, even near the water edge…. I then said to myself these little things have made little tunnels… so might we, by adopting some corresponding means of protection…”
2:18
Fran Scott: The little worm secreted a mucous as it bored into the wood, which lined the hole and hardened to protect the creature from swelling wood and the rush of the waves. The idea for the tunnelling shield was born.
The early machine was a wooden structure formed lots of little boxes of cells, each containing a miner who would excavate their section of tunnel while being protected by the structure.
2:54
James Chappelow (as Marc Brunel): “…thus 36 excavators or miners can be equally protected, one half in cutting out the ground, and the other half, in advancing the frames and securing them by means of powerful screws. In the meantime, a certain number of bricklayers construct the double arch, in brick and roman cement…”
3:15
Fran Scott: Although not without its troubles, the Thames Tunnel was excavated between 1825 and 1843 by what The Times called Brunel’s “capacious apparatus”, and the Victorians had notched up another engineering marvel: the first known tunnel constructed by humans under a navigable river.
And nearly 200 years later, the Thames Tunnel is still in use as part of the London Overground network.
3:51
Fran Scott: Today, the modern TBMs in use on the HS2 project are manufactured by a family-owned company from Schwanau in the Baden-Württemberg region of southwest Germany. This company, which bears the name of its founder Martin Herrenknecht dominates modern TBM tunnelling.
4:16
Martin Herrenknecht: I was born in the region, and I was growing up in Allmannsweier where our factory is now.
4:25
Fran Scott: Martin was working in Switzerland at the time he decided to found ‘Herrenknecht’.
4:31
Martin Herrenknecht: On the Seelisberg Tunnel as a mechanical engineer, it was at that time the longest road tunnel in Switzerland, near the Lake Vierwaldstaetter.
4:42
Fran Scott: That’s ‘Lake Lucerne’
4:45
Martin Herrenknecht: And then I started in 1975 with an engineering office… a small office. My idea was always to have 100 people employed, you know, then it got a little bit bigger.
5:00
Fran Scott: The growth in demand for tunnelling as the world population booms and countries rapidly urbanise has been incredible.
Connections between cities are also feeding demand, with China building around 26,000 miles of High-Speed Rail within 20 years, complete with the thousands of tunnels needed to traverse more rugged topographies and pass beneath urban centres.
5:31
Martin Herrenknecht: High performance tunnels define how people and things move around. There is huge demand to build subterranean infrastructure faster.
5:43
Fran Scott: It is a story that is repeated everywhere you look and this growth in demand has allowed modern tunnelling technology to reach an incredible level of maturity and reliability.
Back in 1975 though…
6:00
Martin Herrenknecht: It was much more simple. You know, we started with pipe jacking machines for the excavator machine with service out and compressed air. At that time lots of sewage tunnels had to be built in Germany.
6:18
Fran Scott: The machines were small, just one to four metres in diameter for simple works. And Martin says the operator had to “feel the ground and “feel the machine” a lot more than today.
6:31
Martin Herrenknecht: Simple tools, if you see them against today’s machines. Today’s machines have thousands of sensors and all relevant TBM data is available to the operator. In real time.
6:51
Fran Scott: The physical capabilities of the machines have improved immensely too. Since the seventies, tunnelling advance rates have at least trebled, even in the worst conditions. With innovations that allow continuous advance, this is still improving.
And with tunnelling taking place so efficiently and quickly, to allow projects to develop with a programme that suits them… rather than being held back by technological limitations.
7:28
Martin Herrenknecht: In the UK phase one of the High Speed 2 rail project is taking an exceptional 10 years only from vision to implementation… In Germany it takes 50 years. It’s a moment we have to speed up [laughs]… so congratulations to England.
7:48
Fran Scott: HS2 will make use of ten of these machines. Each of them is 10m in diameter, hundreds of metres long, hundreds of tonnes in weight and with a thrusting force measured in hundreds of millions of Newtons.
Tunnelling is an incredibly expensive business, and we only do it when the alternatives are unpalatable or not possible. That is why we have historically tunnelled in these dense, urban environments. Where surface space is so scarce and valuable that it makes the use of underground space worthwhile.
Now we also tunnel to avoid environmental or cultural damage. We tunnel below an area of outstanding natural beauty… or to avoid impacting on a community. In fact, in Phase 1, nearly half of the phase one route will be in tunnels.
8:46
Fran Scott: But this much tunnelling presents its own complications, and requires incredible skill from the cutting edge of the infrastructure sector. It is impossible to perfectly understand the underground environment prior to tunnelling. Even the most extensive ground investigation programme in British history only gives a best estimate… geotechnical conditions can vary metre by metre and moment to moment, and tunnel engineers must anticipate what they can, react quickly to what they can’t, while still building an affordable railway.
But there is so much more to tunnelling than the machinery used to drive the long ‘running tunnels’. There are station caverns, so-called ‘green tunnels’, ventilation shafts, logistics tunnels, and all of the associated support.
9:46
Martyn Noak: My name is Martyn Noak, I’m the Head of Tunnel Engineering for HS2 and I’ve been on the programme for just over a year.
9:54
Fran Scott: Martyn heads HS2’s team of tunnelling experts. They provide advice and support to the contractors and other delivery companies. They look after the tunnelling standards and handle requests for departures from these or the design.
10:09
Martyn Noak: Overall, I’m responsible for ensuring that the tunnels as built are compliant to the requirements that have been set down by the requirements team.
10:17
Fran Scott: The HS2 specification borrows from the recent Crossrail and Thames Tideway projects but the organisation didn’t want to be too prescriptive for its design and construct contractors.
There needs to be room to allow good engineers to do their jobs.
10:35
Martyn Noak: It’s a good technical guide, but they have each then produced their own detailed specifications that then sit alongside it.
10:46
Fran Scott: It prescribes that fire testing needs to happen and how ground movements are analysed, and there are comprehensive TBM specifications. While water ingress and tunnel linings are based on the British Tunnelling Society’s specification.
The tunnelling on HS2 is undeniably ambitious. The longest and deepest tunnel will be the Chiltern tunnel measuring 10 miles long and will go as deep as 90 metres.
Probably the toughest works are in the Euston Tunnel…
11:22
Martyn Noak: They’ve got the most variable ground conditions I would say. So, you’ve got now the good London Clay at the eastern end and as you go westwards, you go into the Lambeth group, you have sand and gravels and so on, some quite high-water bearing areas.
11:44
Fran Scott: Just north of Euston the railway passes under the Camden Winding Vaults, which are effectively enormous underground brick-lined cathedral-like structures…. The HS2 lines go straight underneath them, which will call for an enormous amount of ground treatment to support.
Basically injecting a supporting cementitious grout into the geology to improve its supportive properties.
As you continue north, a 4.5-mile twin tube tunnel will take passengers to Old Oak Common Station, then a further 8.4-miles through the Northolt Tunnel to West Ruislip. And its there that the tunnelling exits the classic London Clay into the sandy, gravelly clay of the Lambeth group. And the chances for voids, or air pockets, and other risks drastically increase here, making the construction of cross-passages between the tunnels for emergency egress a more careful affair… but Northolt will be another site we revisit later in this episode.
13:00
Martyn Noak: And then when we get to the Chiltern tunnels.
13:03
Fran Scott: The Chiltern Tunnels of the project are by far the longest and deepest drives on the project. They run for 10 miles through the chalk hills to the northwest of London and are the first tunnels to be built to protect an Area of Outstanding Natural Beauty, rather than just to get through a city.
13:24
Martyn Noak: They had an initial challenge and within the first 200m of the drive, they had to under cross the M25.
13:31
Fran Scott: That’s London’s orbital motorway.
13:40
Martyn Noak: So obviously, that can’t be allowed to deform or settle in any way. So there was a lot of work they did with National Highways to get the approvals for that was very successful, very little ground movement, very stable. And it was a good piece of work.
13:59
Fran Scott: This can be achieved by taking extra measures to support the ground above the tunnel.
14:05
Martyn Noak: They’ve also under crossed the Misbourne River and a couple of places with very low cover. And that’s in our source protection zone. So there’s a lot of concern that some slurry would escape and we’d end up with cloudy drinking water or the Environmental Agency would need to close down the borehole for a time.
14:26
Fran Scott: A lot of TBMs use a bentonite supporting slurry to help steady the tunnel face during excavation. This is extracted along with the spoil and filtered. If it entered drinking water, it would be considered a pollutant so considerable care needs to be taken.
14:47
Martyn Noak: But again, that passed by very successfully, and Affinity Water are very pleased with what happened.
14:53
Fran Scott: North of the Chiltern Tunnels these are known to the tunnelling industry as cut-and-cover.
15:02
Martyn Noak: Basically, a double precast arch.
A cutting is excavated, and then some blinding cast on the base form a really flat surface. And then the arch itself is made up of five elements, there is a single central wall, and then we have two curved sidewalls and then two arches that then make up the two top pieces which creates a kind of a double arch shape. And then we have got five precast elements.
Each precast element is three metres in length. They have reinforcement, they weigh between 16 and 43 tonnes each and they’re constructed in a dedicated factory.
15:53
Fran Scott: The earth that was removed from the area for the cutting is backfilled. New trees and shrubs are planted and the tunnel blends into the landscape, connecting wildlife habitats along the line of route.
Green tunnels can be less disruptive in situations where a short drive tunnel is needed, and site constraints permit. You cant dig a trench through ancient woodlands, but you can do so if you are only disrupting farmland for a season, for example.
These tunnels are predominantly in mudstones…
16:33
Martyn Noak: And the issue that they have is with heave and potential long-term heave of the cuttings that they’ve been excavating.
16:43
Fran Scott: That is the upwards movement of the ground in response to excavation, which develops over time.
Next comes the Long Itchington Wood tunnel in Warwickshire. This is a short TBM tunnel, just 1 mile long, which is particularly abrupt considering the 125-metre length of a TBM with its backup train.
The tunnel drive is to protect woodland dating to 1600 AD. This is considered ancient in ecological terms and also a Site of Special Scientific Interest with complex ecosystems. If we look below ground, as far as the tunnel is concerned, it is mudstones and clays.
Finally, the Bromford Wood Tunnel is another 3.5-mile TBM tunnel, designed to minimise impact on the local area. It is located just outside Birmingham and is similar geology, but with some sandstone involved as well.
17:52
Fran Scott: But the truly challenging tunnelling, is always when the tunnellers find themselves in a tight space. The Euston throat is that on High Speed 2 and so we need to speak with…
18:03
Eddie Woods: Eddie Woods. I’m Deputy Head of Tunnelling at HS2.
18:08
Fran Scott: Eddie works with Martyn Noak, and generally focuses his energies on the tunnelling required for this Euston area. Which has some of the largest caverns and boxes for transport in British history.
18:20
Eddie Woods: Basically, a cavern is a big tunnel. Here the cavern we’ve got is about 17 metres diameter.
18:28
Fran Scott: Coming into Euston there is a cavern, constructed by sprayed concrete lining, a cavern constructed with a stacked drift, a sprayed concrete lining cross-cut, then a trinocular tunnel that splits the line into three grade-separated bores, before they enter the Euston scissor box and get split into the 10 platforms.
Sounds complicated? Well…it is. But the main thing to know is that opening up a large hole in the ground, in close proximity to other large holes, requires very careful design and support measures.
19:02
Eddie Woods: Well, if you’ve got, if you’ve got one tunnel, which is seven and a half metre diameter, the ground is spanning over one tunnel, when you put another one to it, then if they’re both going at the same time, then that ground in between the two tunnels is getting the stress from both. Basically, your ground is arching over both tunnels, which is a much longer span. So that’s why you stagger it.
And also if I have a problem with one tunnel, it’s easier to deal with. But if you have the two tunnels in parallel, running next to each other, you have a much bigger problem.
19:38
Fran Scott: But if the works are large to begin with, more care is needed. Fortunately, all of the Euston works are in the good London Clay, and at least no ground treatment is needed.
Most of these works will be constructed using a methodology named after the lining itself, SCL, sprayed concrete lining.
19:58
Eddie Woods: If you’re doing a larger tunnel, then you’ll break it down into small faces.
20:04
Fran Scott: Dig sections of the overall tunnel profile out one at a time. You could excavate two tunnels at the bottom right and left of a cavern face first, called sidewall drifts for example. Then you are left with an apple core shape in the middle.
Or you could excavate the top heading, then lower down the bench excavation. These are much safer and more stable than tackling the entire arch in one go.
For the very largest section of cavern, Eddie and the SCS delivery team have opted for the most conservative methodology in their arsenal: the ‘stacked drift’.
20:46
Eddie Woods: It’s a safer approach compared to a side drift or anything like that. Basically, you’re making an arch, a massive, big concrete arch about a minimum of a metre thick. The joints between two stacked drifts it’s about a metre thick, so you’ve got this huge big concrete arch before you actually do the bulk excavation.
21:08
Fran Scott: The arch is in fact a series of tunnels excavated in an umbrella above the eventual cavern which will support the ground against collapse. So effectively, pre-tunnel…tunnels.
21:21
Fran Scott: So if tunnelling is the ‘aristocrat of engineering’, what is it that impresses the tunnellers?
21:28
Eddie Woods: I think the design of the caverns is this thing that is very, very… neat. And it’s probably taken it beyond anything that’s ever been done before.
SCL is a very staged excavation process. All this is done in small little advances, and they’ve modelled every excavation stage. And then that takes account of excavating, allowing the ground to relax a little bit, putting on spray concrete, that ageing to take a certain amount of load, and then doing the next bit, and then all these different increments and all that has been built into this. What we found by doing that is they ended up with quite a lot of compression in this.
22:11
Fran Scott: Compression in an arch means added strength. Which means potentially less reinforcement or a thinner lining not only saving on cost and materials but also reducing heath and safety risks to the workforce.
22:24
Eddie Woods: I think a team in Salzburg found before by doing some instrumentation and monitoring, if you have all that compression in there, then the amount of rebar you need around these openings is significantly reduced.
22:33
Fran Scott: This is a fantastic opportunity in theory, but High Speed 2 has to adopt procedures that offer the greatest protection in locations as sensitive as the Euston throat…
22:48
Eddie Woods: We have an independent tunnel expert panel. And they were not happy with the concept of using that to reduce the amount of rebar. And that’s why you have a panel.
23:01
Fran Scott: Perhaps below the centre of the capital is not the location for engineering to be pushed to its limits, but HS2 wanted to take the opportunity to allow future projects to benefit from its experience…
23:15
Eddie Woods: However, what we’ve asked SCS to do, what we’ve asked them to do, or, I’ve encouraged them to do, is to instrument this because I’d like to, I like to design things on knowledge rather than ignorance.
The load can depend on the ground conditions. London clay as we know, is over consolidated, so there’s high locked in lateral pressure compared to the vertical load. So that phenomena, because you can change the shape of the tunnel to take account of the compressive load from the ground. If you’ve got a high compressive load in a flatter arch is beneficial.
23:56
Fran Scott: It is often said in industry that it is in the gift of the larger projects to innovate and adopt new widgets and processes… but it is also possible for them to take a moment for study, and add to industry knowledge to improve future works. And that is exactly what the team are doing here. They are advancing our knowledge of how to build tunnels.
24:25
Fran Scott: The tunnelling required for High Speed 2 Phase One has never been seen before in British history, and is the main reason this is the largest infrastructure project in Europe. There is even a half-mile, 6.2m-diameter tunnel just for temporary logistics and site-supply being built in London. It is truly a project of megaprojects, and we couldn’t take you to every site, but one we chose was Northolt West.
Northolt is an SCS site, and SCS is led by the Swedish contracting giant Skanska. Anders Danielsson the company’s CEO believes other countries, such as his home country Sweden, can learn from the project, as they consider their own high speed rail projects.
25:19
Anders Danielsson: My name is Anders Danielsson, I’m the president and CEO of Skanska. I’m most impressed with the people. All the skilled people were gathered around the world to be able to execute the project like this, and that that’s impressive.
25:39
Fran Scott: From an industry perspective, Anders believes that public investments such as HS2 provide a critical opportunity for skills.
25:50
Anders Danielsson: I think it’s critical, crucial. Great job, obviously, on this project, where we, in this joint venture, we are in between four and 5000 people employed, if you include the supply chain, and overall the project is employing 29,000 people, so it’s a major difference, differentiate their incomes to creating jobs, and also, of course, to invest in infrastructure that can take down the carbon emissions that’s critical for the environment going forward. So that’s something that we really see want to see more of.
My hope is that Sweden continues to invest in infrastructure, even if it’s high speed or not.
26:46
Fran Scott: It is small wonder that the famous British tunneller Sir Harold Harding once called the profession ‘the aristocrat of engineering’.
And fighting against this uncertainty is pitched the emblem of modern tunnelling, the Tunnel Boring Machine or ‘TBM’. These cylindrical mole-like machines are miracles of modern engineering.
Effectively they are submarines that pass through rock with a rotating cutter head, a screw conveyor to remove spoil from the face, a conveyor to take the spoil back to the surface, and an erector arm that places precast concrete segments in rings to form the tunnel.
And each machine leaves an excavated tunnel that is perfectly lined with these concrete rings.
27:45
Fran Scott: Daniel Worsley is the Engineering Manager for Northolt Tunnels West, he is responsible for keeping things moving forward on the dig.
27:54
Daniel Worsley: The machine itself has been fine. We have back-end issues.
28:03
Fran Scott: The back-end of the Tunnel Boring Machine houses all the support services and earth or ‘muck’ removal systems.
28:11
Daniel Worsley: Muck away. So it’s how quickly we can move them up. So last week, when we got settled with some muck issues, we got some we were making 8 to10 rings a day, which is actually better than expected.
28:31
Fran Scott: The 8.4 mile Northholt tunnel is being constructed using four tunnel boring machines in two phases, known as ‘Northolt Tunnel West’ and ‘Northolt Tunnel East’.
Two machines, each weighing over 2,000 tonnes and measuring 140 metres in length, Sushila and Caroline, are being used to create the first section of tunnel. Each is operated by 15 people, working in shifts. While one bore is having some muck issues, the other has…
29:00
Daniel Worsley: Nothing unexpected. I mean, we’re only 107 rings in so. So, we started out with very mixed face and third, third, third. We had foam concrete right at the portal to allow us to build a great slab for the assembly. So we needed a 650 tonne assembly crane, we had to dig out some of the clay and put in four metres of foam concrete. Once we got past that, the London clay is thinning out. Also as as we’re driving we’re getting less London clay in the crown. And then we’ve got a combination of Harrage Group and Lambeth. We’re just into the Lambeth group now.
29:52
Fran Scott: The forward progress of a TBM through the ground is known as the advance rate. Northolt tunnels are seeing rates at launch of up to 20m a day.
30:03
Michael Greiner: So far the maximum achieved was 20m. But we are still in a starting up and training phase so we are definitely confident there is more possible.
30:12
Fran Scott: This is Michael Greiner, the Tunnel Manager for SCS. And at this point the tunnelling machines are still getting warmed up, it takes operators a mile or so to get a feel for how the machine is operating and how the ground is behaving before they can really crank up the speed.
But even getting to launch the machine has been a challenge on this long, thin site.
30:37
Michael Greiner: The shape of the site definitely provides some logistical challenges, mainly in the setup phase because in the setup phase we have a very long stretched construction site, where we are going lots of stages to maximise productivity, we are working in a lot of places. But the long shape brings challenges that need to be managed. We need to have traffic in and out, we need to make sure we have teams working alongside each other to maximise productivity.
31:11
Fran Scott: With the TBM fully assembled in this launch site, and now cutting its way through the ground the, spoil is brought from the cutting head by a screw conveyor and transported out of the tunnel and loaded onto trucks. Later, a railhead will be built to take muck away on rail and relieve some congestion on local roads.
And back in the tunnel with the earth removed, the support needs to be put up. This comes in the form of segmented rings. A full concrete ring divided into equal segments and a key stone, much like a tradition bridge arch but going all the way round.
31:54
Michael Greiner: Here in the Northolt tunnels west the inside of the tunnel is 8.8m, the thickness of the segments is 35cm, we’ve got 7 segments forming one ring and the segments have a length of 1.9m and they are reinforced with rebar cages, depending on the loading we have different rebar cages. We want to optimise the cost and lower the carbon we are using.
32:29
Fran Scott: The rings along the alignment uniform, expect where a cross passage is needed. A cross passage is a link between the two tunnel bores. This is vital in an emergency situation to allow a second route of escape, but they also help with maintenance and access requirements through the life of the railway.
At these cross passages strengthened ring segments are needed, so that some may be removed to excavate the cross passage and the remaining rings take the load.
33:06
Michael Greiner: The cross passage construction over here in the west there are several stage involved. As we have got water bearing conditions. The first stage we do ground water mitigation. That is ranging from depressurisation up to full ice rings.
33:29
Daniel Worsley: The first one is one of the ones that’s required ground freezing. So there’s a combination of ground freezing and just de-watering. It’s a combination of geology and the groundwater and the ground pressures as well. Unexpected inflows so yes, where we expect higher inflows is where we deal with the freezing.
33:48
Fran Scott: Ground freezing is a method of ground stabilisation where the ground is frozen hard by pumping freezing cold saline water through pipes in the ground that have predrilled holes in them. Once the ground is frozen solid it is much more stable and easier to dig through.
Ground freezing isn’t the only smart solution being employed on the project to make things safer and more efficient. As tunnelling progresses around the clock, the team are utilising the latest in mobile monitoring technology to keep them aware of everything happening on site, even when they are miles away.
34:26
Daniel Worsley: While I’m commuting here in the morning, I’m checking the face pressures, seeing how many rings we built during the night, seeing where we are in location to other structures.
34:41
Fran Scott: The same way your phone might prompt you with a reminder in the morning, Daniel’s phone gives him alerts on any issues that might be developing underground, such as too much muck coming out of the tunnel – a possible indicator that something is going wrong at the cutting face.
34:57
Daniel Worsley: Over excavation so if we get 20% above theoretical volume. Over grouting ,so again, if we get 15-20%, it’s an alarm that “why are we putting so much grout”
35:19
Fran Scott: Taking out too much muck and putting in too much grout could indicate you have hit a bad patch of ground. As the machine advances 1m it should take out that same volume in muck. If it takes out more, it could be taking muck from above the machine and cause a sink hole. These monitoring and alarm systems help significantly reduce the risks in tunnelling.
35:46
Fran Scott: Along the entire route of HS2, underground and overground, engineers are employing the most sophisticated technologies to deliver the project safely and efficiently. But as the tunnelling works demonstrate, they are not only relying on what has come before them, the teams on HS2 are expanding our engineering knowledge by gathering data, trialling new technologies, new methodologies and helping develop a highly skilled workforce to realise Britain’s future infrastructure ambitions.
And in this episode we have seen how the trains have cut under obstacles, next episode, we will see how they fly over them…
36:43
Fran Scott: Next time on How to Build a Railway
36:47
Billy Ahluwalia: So the bridge industry has evolved
36:52
David Smith: We’re committed to good design, and good design is not just being about function.
36:57
Laura Kidd: Right at the beginning we realised that this was going to be a major, probably the viaduct of the project.
37:04
Billy Ahluwalia: So you do need to consider the typography. You need to consider what obstacles we’re crossing.
37:12
David Smith: So not just designing something that is economic to build, quick to put in place, but actually looks very, very functional for the rest of its life. All bridges are built for 120 years.
37:24
Billy Ahluwalia: Infrastructure like this lasts for hundreds of years. And it’s a legacy.
37:43
Fran Scott: Your host has been me Fran Scott.
Thanks to our guests Martin Herrenknecht, Martyn Noak, Eddie Woods Anders Danielsson, Michael Greiner and Daniel Worsley.
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