Do an internet search on ‘Alison Norrish’ and two people come up. One is a tunneller who is at the top of her profession: she is a Director and Fellow of Arup, where she has been designer and project manager on Crossrail and Thames Tideway and is renowned for her technical expertise. Before Arup she worked on several metro systems in Asia; getting tunnels built in dense urban environments is her speciality. The other Alison Norrish is a rowing cox who competed in the 1988 Seoul Olympics and who steered her team to a silver medal in the 1986 Commonwealth Games, and who also coxed Oxford to victory in the 1989 University Boat Race. (She did postgraduate work at Cambridge after that. “But I never wrote the b…. thing up. So you can’t call me Doctor.”)
The internet biographies of the rower at no point mention tunnelling, and the biographies of the tunneller make no mention of rowing or sport. They are one and the same person. Here we will focus on her work in tunnels.
In talking about tunnelling under cities, she says that is happening more and more – and getting more and more difficult – with each passing year.
“London has been active in constructing an underground system for over 150 years, but there are many new entrants. That is significantly so in South East Asia, but all over the world cities are building up their urban underground metro systems, and they are doing it now, and some of them are doing it at enormous pace.
“If you look at what’s happening in Singapore, where I spent many years on various phases of their metro system, the rate at which new lines are going in is absolutely amazing. Hong Kong is also at the forefront of that. But cities like Seoul and Taipei and others are really coming up. In the Americas, the Second Avenue Subway Phase Two is being planned. So everywhere you look there is a need for an increasing density and reach and capacity of urban underground metro systems. We now have quite a lot of cities with really extensive networks, and that is only going to increase.”
But extending networks becomes increasingly difficult. “If you think about it, of course it has to get harder and harder, because the cities have already put things underground. For instance on Crossrail, which went basically through London from East to West, we crossed twelve existing underground lines; and every time you encounter one of those, you have to go above it or below it. You end up with a real kind of spaghetti. And of course the next new line that goes in will face not twelve but thirteen lines that it has to cross. So it becomes increasingly difficult to find vertical and horizontal alignments that avoid existing tunnels.”
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By GlobalDataThere is more: “Not only are we getting more congested underground, but we’re also getting higher and higher above ground. So you have buildings that now are piled on ever-deeper foundations. Again just with the example of London, back in the day the big buildings more or less just sat on the ground. But from the 1920s to the 1960s they started to put in caissons and big piles, and deep foundations at the bottom of piles. And then more recently, from the 70s to today we’ve got straight shafted piles that go deeper and deeper, supporting higher and higher structures. So your tunnels have also got to weave their way around that.
“And again in London you’ve got some very deep sewers that Bazalgette and the Victorians put in to deal with the sewage of an ever-expanding city; you have to avoid all of those as well. Whatever city you are in, it is getting increasingly difficult and congested to try and find vertical and horizontal alignments for these new urban lines and connectivity that are needed and necessary.”
A solution, of course, is to go ever deeper to avoid what it there already. It is not, she says, a good solution.
“That is the easiest thing to do on paper if you like. But if you do that then you end up with really deep stations. As an engineer, that’s not a problem. I love to build complex structures deep underground in interesting soil. Can you think of anything more challenging and fun?
“But the truth is, we are not actually building for engineers. We are not even building for cities or for transit authorities. We are building for passengers. And, really, we have got to keep reminding ourselves as engineers that what we are building is a facility to get real actual people from one place to another. And just going deeper and deeper is actually, for people, very counterproductive.
“The deepest station on the London underground is Westminster. For congestion reasons, the new Jubilee line there had to go more than 40 metres below ground level. You take four escalator flights to get to the lowest platform. And you know that’s actually a bit of a pain for people at the end of a hard working day when they just want to go home. Personally, I love Westminster station. You can see all of the structure of it as you go down those escalators, it’s just a fantastic piece of engineering and I think a lot of people that use it love it as well. But the rule of thumb is that if a station is deeper than about 35 metres it’s not fun to use. You’ve just got to go down too far, it takes too long, you feel you’ve got less and less natural light. It’s not user friendly.
“So even though congestion is sort of forcing things potentially deeper I think it’s our responsibility as engineers to remind ourselves that we’re serving the public, the user.
“And, therefore, what we should be doing is using is all our skill and experience – and frankly sometimes bravery – to work with designers and contractors, with utility owners, with asset owners to actually challenge ourselves to keep these lines and keep in particular these stations at a high level. As engineers, we have to re-calibrate our thoughts and use our skills and our experience and our knowledge and these new methodologies to keep the alignment and, in particular the stations, shallow.”
It might not be easy, but it can be done:
“It means that sometimes you’re having to do tunnelling in very low cover, so you are literally trying to support a road with just a metre of structure above your tunnelling. But there are some great ways of doing that, with grouting or by actually putting in structures to support the facilities above. Certainly in Singapore and Japan there have been some really excellent examples of this.
“We have tunnel boring machines now that let us control ground movement much better than we could previously. With them we’ve built up our experience, and our bravery if you like; it has given us confirmation that we can, if we design for it, deal with tunnels in very close proximity. I’m talking about both new and proposed tunnel builds: we used typically to space twin bore tunnels at least a couple of tunnel diameters apart because we were worried about the influence of one tunnel on another. We can put them closer together now.
We can tunnel in all sorts of ground conditions and go for much more closeproximity tunnelling; we can squeeze our tunnels through the eye of the needle if you like, through these physical constraints in a way that we would have felt much harder in the past. So for instance at Bond Street on the Elizabeth line” (which is what Crossrail is now called) “we went within a metre of an existing tunnel”.
She is talking her own experience here. “One of the stations where I was on-site as engineering manager was Liverpool Steet. There we went under the Northern Line within a couple of metres, and the Northern Line is in old cast iron tunnels and is probably one of the busiest, underground metro lines in London and in the world. And it had to keep running; so tunnelling beneath it with that kind of proximity was a pretty scary thing to do. We predicted some 100 millimetres of movement for those existing tunnels, and we pretty much got exactly what we predicted, and we were able to show that the kinematic envelope involved would be okay even with those movements being imposed. And indeed they were okay, and there was no negative impact on the operation of the Northern Line when we were tunnelling for Crossrail.
“So it can be done. And then the feedback loop of our experience of having done it allows future tunnellers to do similar things in different places and in different conditions and builds our confidence as engineers and as designers and then as contractors that we will be able to do it safely. A combination of improvements in equipment and methodologies and our own understanding of the art of the possible allows us to do more and more.”
When you are looking for an alignment through a very congested urban environment, knowledge helps. “It’s as Donald Rumsfeld put it: You’ve got your known knowns – you certainly know where existing rail lines are. There are known unknowns – for example a high rise building in that location that you’re pretty sure is going to be on deep foundations, but you might not know what those deep foundations are.
“And then you’ve got unknown unknowns. In London, in Victorian days, people used to draw their own water out of wells, typically made of cast iron, going all the way through to the underlying aquifer. So those are all over the place and we had no idea where they might come. So we had to try to plot our way through that.”
Data helps too. “We have recently been looking at Crossrail 2, which is a North- South line proposed in London, which would be even longer and go through even more congested regions than Crossrail One. We used open source data on that, that showed for instance what the height and the age of the buildings are. Put that information in with the geology and with our engineering knowledge and experience, and we can project or make an informed estimate of – guess if you like – what the likely foundations of those buildings are. You can call it BIM if you like, or geospatial modelling. But all that digital mapping just tells you is what the problem is – It certainly doesn’t solve it for you.”
She has also worked on Tideway, the £4.3 bn sewer project down the middle of the Thames to tackle London’s combined sewage and rainwater overflow problem. On that, I assume that there is not actually too much choice of route. It has got to just follow the river.
I assume wrong. “In truth it didn’t actually have to go under the river. It had to pick up some key locations – the existing outfalls – along the river route, but it could have gone pretty much anywhere in between those points in linking them up. And the river route itself is a bit bizarre: it has huge U-shaped bends in it. It was made by nature, not by an engineer with a ruler.”
But, as with Crossrail, dodging underground obstacles was again the key:
“Given that all of those link points were along the river, of course the one place that you know you don’t have high rise buildings is in the middle of the river. So it doesn’t take a genius to think that, even if it is a longer route, following the river to link up these key river locations was a pretty good idea.
“And that’s indeed what they did. And it was absolutely driven by the lack of physical constraint within the river footprint.”
The river played its part in Crossrail as well; it was a conduit for muck removal. “Much of it went by barge, ultimately out to Wallasey Island which is a bird sanctuary at the end of the Thames estuary.” While it took investment, winning benefits came for the birds, the muck, and the roads which were kept free of trucks, she says.
There’s no question that if you think about impact on the environment, big diesel trucks are particularly not fun in urban environments. And they are not safe for pedestrians or cyclists.
“That said, these were safety and environmental benefits bought at very big cost and capital expense commitment for the project and for the taxpayer. I believe they were worth it – and the hope must be that planners and politicians – and the poor taxpayers – come increasingly to share such beliefs.”
Because impacts like those are not just important; they are becoming more than important, she says. “Suddenly an engineer or a designer is faced with drivers that that include time and money, as they always have, but absolutely must now include how what we’re doing impacts on climate, on environment, and on the communities that we are serving. There’s no question about that – and it is actually a delight. It becomes a more complex environment that we are operating in, but it’s also a more fun environment, I think, and a more challenging environment for a designer to negotiate.
“When I started my career as a designer and engineer I used frankly to care just about time and money. They were the big drivers in those days and not much else mattered, if I’m being strictly honest with you.
“But nowadays, time and money are still absolutely critical – and you can never get away from that – but we also have to think about all sorts of other things.” Such as people and the planet.
“It used to be, in Singapore and other places when I started designing big underground structures, that we designed so that so the excavations could be made and so that the structure didn’t fall down. So you were basically designing the structures to restrain the soil and the water, to deal with those forces and not to collapse.
“But now we are doing much more, designing to control movements and to control cracks and the like, with a view to increase the durability and the design life of our structures. What that means is that a lot more steel and concrete is being used than is required to just allow the excavation to be safely made. Designing for durability does not necessarily mean designing for longer life and could, under many circumstances, be overdesigning.
“As an example, we have been building tunnels for hundreds of years and tunnels tend to leak. Water is usually present in the ground and will find its way in. That’s just the nature of it. We used to know that tunnels leaked, and we would deal with the water.
“Now what tends to happen is that clients and others say ‘I want my tunnel to be completely dry’ – and of course we can do it. It puts often a requirement to have, for instance, a waterproof membrane and a secondary lining in your tunnel. So that adds massive amounts of materials, of time, of money, and of impact on the planet – and it is to solve a criterion that you may not need to solve. Why not just pump out the water, or let it drain out of the end?
“The other thing that demanding dryness does is increase the risk for contractors and designers. If they fail to achieve that criterion they will get taken to the cleaners. In the blame culture that we exist in at the moment, where the client pushes all the risk to the contractor with these very high – and unnecessary – requirements like the tunnel having to be completely dry, then the contractor of course will price those huge amounts of risk into their proposal and their fee. So it drives up costs and it drives very poor behaviour. And it doesn’t allow lean and efficient design.
“So sometimes I believe we’re not thinking about those important criteria, of time and money and impact. Because we need to be using less material to achieve the functionality that we are wanting, and yet some of the codes and some of the requirements, whether for crack width control or for waterproofing or for whatever, make us specify things that cost a lot of time, money and material and therefore impact to achieve, when I would question why we are trying to achieve these things at all. Could go for a less aesthetically-perfect solution, but one that works?
“If I look at some of the structures that we built in Crossrail, the amount of steel going into these diaphragm walls was absolutely massive – and steel is not something you want to be using unless you have to. So I would be questioning why we were designing to control crack widths, which in themselves are only important to try to protect the steel from corrosion, when we were in an anaerobic environment where corrosion isn’t possible! Too often we are designing for things that either don’t necessarily exist, or that could be controlled another way. We don’t always need Rolls Royce solutions. A standard mass-market production car will still get you from A to B, and anywhere else.
“So often we are setting our sights too high, and unnecessarily high, and in doing so we are having a negative effect on the climate, the environment, the material use, the cost and the planet. There are times when a more basic solution would do.
“I think we have to change our thinking here, as a profession and as an industry; and the change needs to include the whole chain. It needs the clients to rethink what they are trying to achieve and therefore the requirements that they set; it needs the designers to really understand what they’re doing and not simply do something that is safe that won’t call on their professional indemnity insurance . It needs contractors also to be confident. And it needs all of those people to have the same purpose and to work together in a contractual environment that allows lean and efficient design. We are currently in an industry where the opposite is the case, so that the contractual environment encourages over-design in the supposed name of safety. And, I think, we really ought to look at that; and we can only do that with clients that are willing to allocate risk where it’s most appropriately managed.
“I’m a designer, I love designing. I don’t know anything better than a Friday afternoon with a geological long section and some colouring pencils. I mean that’s my idea of heaven. I like to design things that are elegant, that do the job but don’t use any additional material to do so. That’s the fun bit of being a designer, but the industry that we currently inhabit does not reward and incentivise that behaviour.
“So everyone has to be braver, both in their engineering techniques and their approach and their designs – and in their desire for what the final project is about. We should acknowledge that client and designer and contractor are not adversaries but that actually we are all in this together. Basically, everyone should have a little more courage.”
