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hello and welcome to technically speaking where scientists and engineers come together to chat about a common interest share knowledge and satisfy some curiosity I'm Ellie and this week I'm joined by Rwayda and Laura to talk about the challenges of constructing undersea tunnels and an Innovative new project now fortunately we have Rwayda with us this week and she's a civil engineer so I'm guessing you know a lot about this well I think I know few about it um not not a
lot we'll take a fair amount which is certainly more than I know Laura what's your interest in this well I'm not a civil engineer although I have worked alongside different aspects of civil engineering over the years but I came across this article about this huge construction project to create an undersea tunnel in China which would reduce Journeys times from an hour to just 5 minutes wow yeah the tunnel is flexible and it's made from concrete which I think seems like a bit of an odd
thing you don't tend to think of concrete as being flexible but it also seems to involve lots of Novel technology and construction methods that I thought ooh well this is intriguing I'll ask rer about them consider me intrigued as well like I said I know nothing about this so Reda how do you make a flexible concrete tunnel and what do you need and why do you need to do this apparently in this case they use this new technique when they would the preast things on site and that's why
they have on site lab so Pras concrete itself is not new but the way they're using it here is new so they do it on land then take it on um a a boat submerge it to the water go again and get the next section and the flexibility comes from joining these sections together yeah I read an article that said it had some sort of a special bar in inverted commas CU that makes it sound really exciting it would transm these sheer forces so you know that's when you apply
forces in opposite directions kind of like tearing a piece of paper from what I've read transmitting those sheer forces means the tunnel is less likely to fracture so I guess that's part of what makes it flexible in a way yeah I think so and they said they also pre-stress the concrete which helped make it flexible uh which from what I can gather means that they just stretched it but I don't think that's anything new is it I reckon they made it like sit a load of exams just made it
really stressed stress out stress it out before they put it underwater a good a good way of of thinking of pritus concrete if you hold like a pack of books and press them together you can add more books on the top of the Pressed books right and this is the whole idea of the pre-stress cuz you're adding stress to a specific point within the concrete and the idea of that concrete is started in the 1800s there are a lot of pre-stressed concrete now but I think
the the the nobility here is in between using these sheer bars that Laura talked about I think these Shear bars have joined the sections as well as joining within kind of the tube itself when they submerge it and I think that would help the sections to be bonded with each other this is my understanding I'm assuming a lot CU I not find much information so if we take a little step back this is the Dagan Bay undersea tunnel that we're talking about here with all these fancy
new uh novel techniques and pre-stressed concrete so why is this so exciting what's the big draw for this project well it w Global project of the year which I assume is a big thing in civil engineering terms and I think it was that was partly because of the mix of first of kind Technologies and also the new construction methods that they used Roa was saying they had this tube Factory on site they kind of improved the construction as they went on site they could get the
time it took to sync each tube section of the tube they got that Tim down really really short in the end it was like a four-year project they had quite a long time to iterate and improve things yeah and it seemed to been have suggested first in the early 1990s but was not achievable until now because of the location one of the things I was reading about is how cold the water is around there so it's really difficult to build and that's why it's much more noble now I think they needed
a better techniques to build it so this sounds pretty sort of at the Forefront of what we would call these engineering Marvel I suppose so they've built this tunnel and it cuts down the time from getting from A to B instead of being 60 minutes it's only 5 minutes and it took 4 years to build do we know how long it is so it's about 5 kilm so that's I mean that's a pretty decent undertaking to build an underwater tunnel and I have no concept of this but you were saying that
the water is cold so like what sort of things are they doing on this on-site lab then to look at like how they're going to put it into the water oh well I think they would have investigated how the concrete would react to that water what type of bond you will have and they would possibly be testing on site to see the effect of that and I think we will also need to think about salt right because it's C so it's a salty water so that would also affect the concrete so
when we think of concrete is not only concrete concrete comes with rebar with steel rebar in them and once the salt gets in they get the rebar to corrode and then your section would fail so I'm assuming they have done on-site testing to see the impact of the environment in including seaal including the kind of cycles of freezing and thrwing from the cold water as well the other thing they did they kind of like digged the bottom bed of the sea but then they have a full
section of a tunnel submerged in so I think that was also not an easy procedure to fit yeah I imagine that's very difficult if they're looking then at the effects of the salt and all the things and they're digging into the seab B were they then looking at the like surrounding marine environment and the foundations or like was there anything done to prepare the sea floor or what other experiments might theyve been up to they prepar the seabed but there is no where they said that they they gain a
foundation which also I find strange but they prepare the seabed this is my understanding then they have their Precast segments of the tunnel submerged to the seabed that they prepar I read something about a rip wrap layer which I think is just a load of stones they put on the sea Flor in some sections which would help level it and create the right shape oh my goodness I didn't even think of the sea Flor as like not being perfectly flat but like obviously why would it be but if you've
got a tunnel that's then going like wibbly wobbly up and down under the ocean that's that's not what you want for getting somewhere quicker I know I'm not even sure that the sea floor is all the same type of rock cuz the article I read mentioned some of it's on clay and some of it's on like hard Bedrock as well and that surely they're going to react differently to different environmental stresses right so if there's a temperature change one might expand more than the other also surely
Clay is a nightmare to build on isn't it it is a nightmare to build on and and usually you try to avoid it the other thing that got this article got me to think about what is the anchoring mechanism for that tunnel to stay in you submerged it but what is holding it down you have air in it yeah we should stress I think maybe we haven't made this clear that this is massive this is a six Lane car tunnel so this is not like some little tube to run you know internet
cables through or you know gas pipes this is like a six Lane Motorway essentially Under the Sea yeah and they're heavy tubes as well I think each segment weighs is it over like um 7,000 metric tons I think I think so yeah that's something like that I don't understand right forgive me for not being an engineer here if you're making sections and you're sinking them into the seabed right how are you then connecting them so that the water isn't going through them at any point like if
you've got section one and section two they've sunk is there like a trap door that they then like to like I don't understand they said somewhere that the level of Tolerance was 01 a millimeter wow yeah like the tolerance that seems tiny yeah yeah considering how big these tubes are yeah and also they said they use some kind of high performing uh grounding material to fill the gaps so it will not let in the sea yes I wouldn't be surprised if it started off with water in it initially because they
were building this in segments right and putting each segment under sea at a time and then once they connected all the ends they just pumped the water out that's how I do it but I'm not aine that's that's a lot of pumping there isn't it as soon as you let the water in I feel like you're on to a bad start I think they would have gotten some water in them but I don't I think they would have sealed it somehow to have minimum water in because if they let the water
in that fast that mean they have not protected the connectors well these connectors will have some steel showing up in them then that would kind of like Lego blog in into the second side of the tel it's a giant Lego Tunnel underwater pretty much it that's what they're telling us well maybe that was part of some of the on-site testing they did cuz they mentioned 20 different experiments so maybe part of it was looking at how they could grout it and keep it sealed and they also had lots of sensors
embedded into the tunnel in in the concrete I think they could measure all these different parameters which could include is it starting to leak yeah I mean that's surely the big thing that you want to avoid is is it starting to leak I also read that they determined that it could last for 100 years is I think traditionally you build buildings to last 50 years but I think if they designed it for 100 years so that means they would have put in much more effort
in having high performance concrete and all this fancy steel um the other thing that they mentioned is they use this prefabricated or manufactured s manufactur sand what they did IS F got a stone and ground that stone very f so it would fill all the gaps within the sand particles which make it much higher performance and that would make it more workable so it's easier to cast and also make it uh apparently more water resistance so resistance to chlorides and more
resistant to permeability has like less water drop and concrete it was a limestone that they used wasn't it you normally use sand so that would be silica so they replaced silica with calcium carbonate so it's a very different chemistry I have thought yes they have replaced the chemical component to provide more resistant to Chloride yeah yeah I mean I'm glad to see that they were using the manufactured sand they call it even though it's Limestone CU we did that
episode a while ago about we running out of building sand yeah that's where it's all gone to the but no apparently not if it's Limestone they they've left it yeah I would hope they have done longterm testing cuz usually when you test concrete you test 28 days but in these projects they you would want to do some durability testing and that would be you tested at 90 days and 12 days so I'm hoping that they did some of that testing to certify that their concrete would be the same in 100 years but I
don't know how would they do this test and they build it within 4 years unless they started the testing before and they already have some La lab data unsure about the 100 years they looked at other under sea structures as well didn't they that had been in the sea for up to I think it was about 86 years oh that's a good idea I usum they looked at all these different structures and how they were weathering and which components were weathering more slowly and use that
to say if that's happening to these things then to make something that last for 100 years we can extrapolate and do this yeah and I think the sensors cuz they said they have an intelligent Center units which I'm hoping or I thinking I'm thinking it would be collecting data even on some of the chemical component of the concrete it records some sort of chemical changes and if it records that they would know if there is something that they need to fix so that raises another interesting
question then like if you're building it underwater you've got everything down there and one of the sensors then goes off and says something's wrong how do you even go about like fixing it underwater or are they using like cool systems to do this because how I'm also then trying to imagine how they got these giant 700 ton pieces into the sea in the first place I think they will have similar procedures to go and fix it but like placing a whole tennel and fixing parts of it are two different
things I think it's easier to fix little things rather than spacing the whole thing so if they could place the whole thing in and is functional surely they can go down and fix little bits that's why these sensors are very important yeah could you imagine seeing these incredibly heavy very large bits of tube being floated across the bay though no no how weird must that be this massive thing that looks like it probably shouldn't float but it's doing it anyway so that's what they did then
they floated these sections across the water to where they needed to be yes wow H how I hope like they do one of these Mega structures uh episode on it and I think they would right because they would show you how they would have build it CU they will have videos and all of that and I think that would be interesting uh I'm really interested to see how they did actually do it yeah we'll keep an eye out with the documentary then I mean they said they used um this special positioning system
for their barges when they were putting at least it might have been the Rip r layer rather than the big tubes I might be misremembering this but they they normally would just um M these really firmly to the trench that the tunnel is going to lie in and they decided they couldn't do that because it was too risky so they came up with a whole new way of doing it that involved floating barges and this highly accurate Advanced control system they developed just for
this one purpose I think it's pretty impressive I'd like to think that would have other applications in the future yeah I'm sure that they could then give that to someone else to uh use for a different project I I think this whole way of building tubes is novel and I think it would be integrated to other project because it's is the first time they use this way of precasting something then put it under water in a case of a tunnel it's not the traditional way of building the tunnel
so how are they normally just like you just blast out the surrounding Rock underneath the seabird well it's a little bit fancier than this so you have this huge drilling machines traditionally and these drilling machine will go down and drill and you would kind of support that then you start building your tunnel and the drill tube but it's a kind of a heavy machinery way to do it and that's how they build the channel tunnel I'm still disappointed in the channel tunnel I feel like it should
be glass and you should be able to see the fish swimming over you when you go in it yeah you've got me thinking how thick would that glass need to be and how much water is above it so how much pressure is it under I'm not sure I would when it to be glass I'm imagining it like um you know like when you go to an aquarium and you have the like tunnels and the like sharks and the Rays swimmer over you that's what I really wanted as a kid not some like concrete structure that you just sit in your car
for however long know but aren't those aquarium tunnels like the walls a meter thick and it's only supporting like a few meters of water anyway I mean yeah it would have to be like scaled up a million times but still yeah I think we still don't have the technology to BU that glass yet yeah okay it would be cool to see that as he traveling along though see what the marine life is up to and are they looking at you yeah so surely when they did this there must have been loads of like environmental
factors and costs to consider is this a better alternative than just building a bridge well I think the the kind of condition at that location are challenging to build a bridge on it also there is some reservation for the marine life and that why I think by doing the this way and kind of placing things in SE rather than doing them normal construction way they would have preserved some of the environment in that area um also the cost of it was actually High I forgot the number it's not on on
the top of my head but what I was reading about that as well it's really important to link one of these two areas to each other for economical growth yes so I think they're thinking on long term the investment will return by economical growth to the area yeah well could you imagine if the commute is suddenly 5 minutes rather than an hour it would open up all these new job opportunities that you probably wouldn't have considered before I mean that would make your day a lot better you suddenly
shaved a what an hour and I can't do M an hour and 50 minutes off your day yeah and and I was reading for for some of the commute if you go around the day it's about um 8 hours drive wow okay so I think I think the hour is is also like is for certain location they're talking about but if you kind of like your total from these two cities your total distance of travel or time of travel of this8 hours and you chove that down to 30 minutes or so with the extra outside
of the tunnel commute I think that's that's actually would make people from one area work in another it's commutable and clearly they thought like a lot of people were going to use it if they built a six Lane car tunnel in the first place you know it's not just like a standard freeway this is a a pretty big undertaking and I think like they if they're targeting economical growth you would want to build it big in the first place so you don't have to go again and
add to it and rebuild it make it bigger cuz imagine like they if they had to go and and and do more Lanes later on because it's gotten too popular that would be embarrassing I think and also probably incredibly different I think that they just decided just to go big and make it last a 100 years and then you're sort of done with it yeah I think that's the ideaa would you be scared then if you're you know you've waited four five years for this tunnel to be open are you the first one driving
through it are you trusting the engineering and the stressed bars and the all the concrete and everything are you taking the inaugural journey I mean I guess it's 5 minutes but still you could you could drown in 5 minutes I'd rather wait for someone else to try it as say I have a feeling to it's similar to these weak bridges that they get you to drive on and around the rural areas oh yeah when it's a sign that says weak bridge and you're like well could could
we not just make it stronger it's like how weak is it can you tell me like that's how I feel about these things you tell me a weak bridge and I'm an engineer and I'm really having a problem with the weak Bridge sign I don't even notice them it's so funny that you say that because there's been one like on the outskirts of the village where I grew up in my entire life and to my knowledge that bridge has never been changed like it can't be that weak everyone's gone on it for well my entire
lifetime so well it's usually I think this usually comes with a with a limit right so so we could bridge for a Lori maybe not for a car but I think for me I would feel better if they stop putting weak bridge and they say the capacity is X that's fair how about you Laura are you driving through the tunnel I'm yeah I'm assuming it's already been thoroughly tested and if they've opened it and the public can go through it then it must be fine I just think it given my
safety background it would be very weird to let the public go through something that hasn't been thoroughly tested tested so I think I'd be fine with it I wonder like when they were done if they were then like oh yeah we should probably open this now or whether they were just enjoying the tunnel for a little while just without any cars on it I'm sure that they had uh costs to recoup is it free is it a toll tunnel do we know yeah I didn't find anything that says it is but I would like to think if
there's an economic benefit to letting people travel that they wouldn't really charge for it but I'm just a nice person if Laura was in charge of the tunnel you wouldn't be uh putting a toll on that there will be more information coming on that bridge I think soon they'll open it people will use it and they will say how great it is yeah and one of the challenges I found when I was looking into this a lot of the literature seemed to be only available in Chinese which is fine for the people
that built it in China I would need a translator so I was a little bit disappointed by that cuz I'm so fascinated by it I wanted to learn more I'm still mind blown by the fact that you could build a tunnel underwater in the first place like I understand the channel and blasting through the rock like that makes sense to my brain but still I'm not fully on board with the floating giant pieces of concrete into the ocean and then dropping them and then somehow sealing them all together
and making it work but I'm very impressed that lots of other people understand how that happens but I guess you take flights though yeah so you have no problem with getting in a metal tube that's just suspended in the Sky by physics that for some reason is fine for me that makes perfect sense in my head I'm like it's just power it's just power over what air resistance whereas this this upsetting well I think this is the next step in building and development we
started to see some 3D printed concrete structures coming up and I think is will become more I've seen a construction site somewhere in the UK that they started to do 3D printed concrete houses oh cool I think build more efficient and quicker would be the the engineering of the future especially now with the rain of artificial intelligent and robot we'll get artificial intelligence to design the next uh what is it Global Engineering product of the Year o I'm
not too sure I like the idea of that it depends how the AI has been trained doesn't it yeah I suppose so from my little experience on on seeing how people are using that in engineering I would not recomend it I meant artificial intelligence in terms of the monitoring and the sensors and the quality of the material going in okay and necessarily in the design you still need a human there I think yeah if it could have taken all that historic data you know I said that they looked at all the undee
structures that have been around for a while and they figured out how to design something that would last for 100 years the AI could probably have done that I don't know better or quicker or something yeah that's probably true give it a data set to work with pre-train it rather than letting it Loose perhaps on a huge engineering project yes well I feel like we've probably gone off topic just about enough we've covered everything from how you might even begin to build something of this scale what
substances are involved what materials you might need to use and whether you'd even want to try it if you got the opportunity so thank you very much for listening and we'll see you in the next episode The Views expressed in this podcast belong entirely to the person that said them they did not represent any industry or organization if you enjoyed listening to these views it would really help us out if you could rate US leave a review and tell a friend this podcast was sponsored by no one but
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