Sam Sherwood-Hale spoke to Kurt Zeidler, Principal at GALL ZEIDLER Consultants about his career, the history and development of tunnelling and GALL ZEIDLER’s work on HS2

You’ve had a career spanning 35 years, how far back does your involvement in the UK go?

I would say it goes back a long time, I worked in the UK for the first time in 1991 on Crossrail, in its early days and then we founded the company in Austria in 1999 and then first opened a UK office in 2006. Of course, much of my career has been spent working all around the world but with quite a long time in the United States, that’s where I teamed up with Mr Gall and this formed the beginnings of Gall Zeidler. Then I came back to Europe in 2011, I decided it was time to put a bit more effort into the UK office, leaving Mr. Gall to run the operations in America. Of course going back further, it all started in my home country of Austria, where I worked primarily on construction sites, from 1981 to 1990, doing a little bit of design and then I started my own company in 1999.


How has underground construction technology changed during that time?

There have been significant changes, when I started, we used different materials and equipment. I remember my first tunnel was a TBM tunnel, it was a mainframe TBM which is for hard rock but there were no other TBMs available, and their use was very limited. Yet, over the first 20 years of my career the TBMs underwent enormous development, and now we can use them for almost any ground condition. So there has been an adequate development in this period, but it was not a quantum leap, there was a constant, steady improvement, especially in the materials that we use and in quality control, materials became much better known and more reliable which led to more repeatable results. But we haven’t really seen a quantum leap, because the industry is relatively conservative, so progress is slow.

Where the codes regulations are concerned, I have seen the Euro code come into play, which didn’t exist when I started. The Euro codes are relatively widely implemented these days, which is an improvement from the national codes by providing a common base. There are many more specifications and standards in place for materials, there were types of concrete that we tested when I first began my career but there are no universal design standards for fibre reinforced concrete for example, even though we use it quite widely And testing standards for fibre reinforced concrete are available.


In recent years, the 130-year-old Severn Tunnel was made ready for electrification of the South Wales Mainline and Farnworth Tunnel was upgraded to accommodate two electrified lines near Bolton. Gall Zeidler Consultants provided expert design review services as the Category 3 independent design-checking engineer on the Farnworth project, what goes into rehabilitating a tunnel?

Unfortunately, in particular the UK but also in many other countries as well, there is not that much appetite for rehabilitating old tunnels, despite the fact that the infrastructure is aging in all developed countries, because we all started our railways at around the same time. I have had discussions with relevant bodies in the UK for over 20 years about rehabilitation, but they are constrained by operational requirements, budget and timing. But there are specific challenges when it comes to rehabilitating old tunnels and I always try to use this experience I gained with rehabilitating old tunnels in the design for new tunnels, because I realized that for all kinds of reasons, lack of knowledge or lack of adequate materials, certain things were not done the way we would do it today, to make the tunnels live longer. When you start a railway tunnel rehabilitation project, it is typically a requirement of the authority that either the downtime or the closure time has to be limited to the absolute minimum, and you might even have to reopen the track whilst the rehabilitation goes on. That’s certainly a big challenge. And because our infrastructure is so in dire need of refurbishment, because we haven’t done a lot of that work for a long time, this gets more and more pressing, and less and less feasible to have both operations and, and rehabilitation going on at the same time. So that that’s one of the challenges. The other challenge is the lack of documentation.

Typically, where there is a lack of documentation, you can’t really rely on what information you do actually have because there has not always been a strictly standardised system for documenting projects. For example, we worked on a project in Pittsburgh in the USA, where there was this ten-metre-high cavern above the tunnel. During the tunnel construction this area had collapsed, they cleared it out and built a brick arch in this area and then over roughly 100 years, material was falling on top of the brick arch and nobody knew that there was actually a void behind it. So when we got in there, we emptied out the refuse which was sitting atop the brick arch and all of a sudden all we saw was a big hole. And the real shocker for everybody was there was a house above us with a swimming pool. There was only a two and a half metre thick, solid sandstone slab in between us and the house – and nobody knew for decades!

It’s like when you refurbish an old house, there’s always a surprise. Regardless of what you’re trying to plan, there’s always work to do afterwards that is different to what you expected.

So, what we did was build a new arch and then filled the void with concrete, and that was the first time people realized that they had this huge void below them.


So you have to be very creative in that moment, because it’s a problem where there’s no documentation and I imagine there’s not many instances where you’ve got this sort of issue, so it’s likely there’s no precedent to draw upon when you’re coming up with a solution?

When it comes to collapses, there are often no reports on it, so you have to be prepared for all kinds of things. Typically, the condition of the lining itself, if it’s a brick lining, or stone masonry, that’s quite well known before you start. So you can determine the condition of the brickwork, but what’s behind the brickwork can still cause difficulties. There are some tools being used, like ground penetrating radar, but we still need to develop new tools to give us a more reliable picture of the conditions behind the lining. We can map the shape of the tunnel very accurately and see its deformation, but that alone doesn’t tell you the whole story.

A great example of past tunnelling is The Thames tunnel, the world’s first shield-tunnel under a river, which was a gift from Brunel who invented this rectangular shield and used bricks of extraordinary quality. It is unbelievable how hard those bricks were. But one of the other challenges facing these old tunnels is water, which is the prime cause of degradation that comes from the inflow of water inflow. Because in the good old days, we didn’t have a lot of material to act efficiently in such a way to close off the groundwater and avoid ground water intrusion into the lining of the brickwork.


We were talking earlier about tunnel boring machines, TBMs, obviously today they are much more widely utilized in tunnel construction. Is that always by necessity, or is it the case that the technology has just improved so much that people are finding uses for them?

I think it is always demand, unfortunately, I believe we are not tempted to invent new things for something which we don’t have a need for in that moment. The need for soft ground tunnelling machines came from the urban areas, where there is a higher demand for infrastructure, and the vast majority of big cities are built on soft ground. When you look at London, it is a historic city of tunnels and the reason for that is because of its relatively soft ground which is still well suitable for tunnelling.


In your paper, ‘Modern urban tunnelling responding to social needs’, you talked about the socioeconomic reasons for major infrastructure projects, how much of that that has been the focus of your career?

I asked myself very often, why do we do this? Because it’s a major effort, it’s a major investment of money, time, human resources, materials. This paper came from a discussion with my partner where we discussed this very question and wanted to publish an answer – why are we so enthusiastic about HS2 for example? So, instead of being technical, we looked at the potential effect of Crossrail once it is open – things like the value of property but also the reduction in travel time for commuters, which should improve their wellbeing, for some people it cuts their travel time in half.


You’ve worked on Crossrail and on HS2, the Western Rail Link to Heathrow Airport as well. What improvements in sustainability have been made in these more recent projects?

We have improved the durability of the materials and we have tighter quality control, more protection measures like waterproofing so we can prevent the groundwater from flowing into the structure. Structures today probably have 50 to 100 per cent longer lifetimes than traditional structures. There’s always a discussion about the impact on the environment in any of these projects, for quite some time we ignored the environment when we built infrastructure. Anything we do has an effect on the environment and on our surroundings, but we can reduce the negative effects.

For a long time grouting the ground was a generic solution for almost everything, whereas today we are much more efficient with the use of grout and due to the TBM technology, we use much less grout.

When I look at HS2, our involvement is as a designer for the C1 project, the Chiltern Tunnel, and nearby there is a water extraction field which has a lot of pumps extracting drinking water and there was a long discussion about avoiding polluting the groundwater, which could then affect the pump fields. In the past, it would just be accepted that we had to build it so we have to risk doing this harm, but now the mindset has changed about the use of materials, and the use of natural resources as well, so we focus on engineering a solution. Our work in the Chilterns is focussed on designing the 38 cross passages and the portal where the TBM started where we came up with a support system in the portal area to avoid settlements.


Do you think that a tunnel under the Irish Sea linking to Scotland and Northern Ireland feasible?

Absolutely, yes it would be technically feasible, you would probably have to build islands in between where you can have escape shafts and ventilation shafts. Whether financially and economically, it makes sense is a different story, which to be honest, I can’t answer, if you look at the Eurotunnel, it makes much more sense to use that then flying from London to Paris, and there are plans for tunnel projects between Denmark and Sweden, I believe.

For the future of tunnelling, we have to bring down the costs and the time spent on the project, and those are interconnected of course. We need to develop technologies which can increase the speed of tunnelling and reduce the costs of it. We also have to reduce the time involved with general planning, Crossrail is an example, I was personally involved in Crossrail in 1991, and I was there in 2012 when it finally started construction.