Feature article Propping up the wall: how to rescue a leaning tower Image courtesy of John Burland Civil engineer John Burland talks about the perils John Burland in front of the tower and practicalities he helped to save, in Pisa of supporting some of the world’s most iconic buildings. Physics Physics Earth science By Susan Watt History General science “Mexico City Engineering was founded on an ne of the joys of being a civil old volcanic lakeAges of 10+ very, very soft engineer, believes John Bur- volcanic sediments, which are incred- This article offers an insight into the life and work of an engineer: his land, is that “every single ibly compressible,” he says. “Pump- decision to study engineering, how science and engineering methods Oproject is unique; no buildings are ing water from beneath that area for are combined, and his small and large projects. The Leaning Tower of alike”. There is, however, one feature the city’s water supply has caused the Pisa and its problems are well known, but it is especially exciting to shared by most of the buildings on ground to settle, literally by metres. be told the story of how it was saved by the man who did it. which John has worked: they seem to That has caused huge problems, have been in danger of falling down. because theThe settlement topic is interdisciplinary, isn’t uniform. can be easily understood without much Most famously, John was one of the Half of theknowledge Metropolitan of physics, Cathedral and, is because the article is written like an ad- engineering experts called on in 1990 built on anventure, area where can anbe oldused Aztec in many ways and to enhance the teaching of to help rescue the Leaning Tower of temple onceseveral stood, subjects. which compressedTeachers can find their own ways of using the article, Pisa, Italy, but the Big Ben clock tower for example in geography, general science, history, physics or engi- in London, UK, and even the Metro- neering lessons, but also in language lessons, to read and translate the politan Cathedral in Mexico City have article. For students aged 10-15, I would recommend the article for also benefitted from his expertise. general reading, while older students can benefit from it in the context Rescuing the Big Ben clock tower of lessons on engineering. The article is also suitable for comprehension questions such as: The Big Ben project was not so much a rescue as damage limita- · What problems may occur if massive buildings are built on unsta- tion. As a soil mechanics engineer, ble ground? Describe these problems in detail. John was already involved in deep · Which methods can be used to stabilise unsafe ground and how excavation projects in London when do they work? the decision was taken in the early Gerd Vogt, Higher Secondary School for Environment 1970s to build a multi-storey car park and Economics, Yspertal REVIEW underneath the Houses of Parliament www.scienceinschool.org Science in School I Issue 26 : Spring 2013 I 9 and the Big Ben tower. John was ap- Mistake or not, John’s expertise you’re trying to meet them. I don’t proached to help with the design and was again called on years later when, believe you can do anything else,” he construction, to ensure that the state in the early 1990s, an even deeper says. buildings would not be damaged by excavation was needed for an under- the work on the 20 m-deep car park ground train line being run beneath How it all began beneath. The fear was that another fa- the Houses of Parliament. Again As an engineering student, John mous leaning tower might be created, John’s team managed both to measure initially disliked the discipline of this time in London. and to control the movement – by soil mechanics, in which he is now Constant monitoring was crucial pumping cement into the ground regarded as such a prominent expert, to the project, as John recollects: “My before the excavation started – but but warmed to it while studying for team was involved in taking measure- not without a lot of attention from the his PhD at the University of Cam- ments as the car park was constructed, media. “The press got very excited bridge. After Cambridge, he joined and we discovered all sorts of unex- about it, and we still get questions the Building Research Establishment pected things – as you do when you occasionally, and see headlines such (BRE) in London, a UK government take measurements. For example, we as ‘The Palace of Westminster is about research organisation that had pio- predicted that the Big Ben clock tower to subside into the River Thames’,” neered the study of soil mechanics. “I would move towards the east, and it John says. wanted to go there and work on real actually moved westwards. We got John has had a lot of practice at buildings, and find out how they re- the amount right, but we got the di- dealing with the international press, ally behaved,” he says. rection wrong, and we had to explain as well as in tackling technical issues. At BRE John worked on his first to Black Rod [the House of Lords of- So how does he approach this? “My high-profile project – the Sydney ficial] why, even though we were out line is to tell it as it is – say what the Opera House – and honed his skills in by 180°, it wasn’t a serious mistake!” technical challenges are and how foundations and excavations. “I had a wonderful 16 years at BRE work- Image courtesy of John Burland Image courtesy of John ing on all sorts of projects, but one in particular required digging deep excavations in urban areas,” he says. “So I began to get involved with some of the deep excavations that were taking place in London – the Barbi- The new can Arts Centre, for example, which underground train was a huge excavation in the City of station under London. And because of this work, I construction at was asked to become involved with Westminster the Houses of Parliament car park. That became a seminal project that was published in the engineering journals. And I guess it was because of my involvement with that that I got involved with Pisa.” The Leaning Tower of Pisa in danger This was in 1990, when the famous Leaning Tower of Pisa was leaning rather too far for comfort. Not only that, but a medieval tower in the northern Italian town of Pavia had collapsed the previous year, killing four people. So the Italian government set up a multidisciplinary commission of international experts to prevent the Pisa tower meeting the same fate, and John was asked to join it. 10 I Science in School I Issue 26 : Spring 2013 www.scienceinschool.org Feature article of ground it was built on, as John explains: “The ground there is so soft that it’s like foam rubber, and in this situation there’s a critical height for a building of a given weight and di- A cross-section through Burland John of courtesy Image the Leaning Tower of ameter before it starts to lean and fall Pisa, before John and his over. And the Pisa tower is exactly at colleagues began their that critical height: amazing.” work to rescue it So the tower was hovering between stability and collapse. “It was going to fall over, but it was impossible to say when – a storm or an earthquake could have finished it off. So we had to do some very urgent work if we were to stabilise it,” John says. The problem is that once a tower starts leaning, it becomes increasingly unstable. “As the inclination increases, the centre of gravity moves, produc- ing an additional overturning force,” he explains. “So it gets worse and worse, and then it collapses.” At the time, the tower was moving at about 1.5 mm a year, but the movement was Physics accelerating – which was terrifying, John says. Of course, working on such iconic buildings involves more than just engineering. “The problem was In the beginning, not everyone so it’ll never fall down’. So our job incredibly complex, because we had agreed that the tower needed sav- was to bring some science to bear.” to obey the laws of conservation of ing. “There was this huge mythology The first step was to investigate how about the tower. People were saying the tower had been built originally, to ‘Don’t touch it, it’s quite safe as it is; if understand why it was leaning. The you do anything to it, it’ll fall over’,” team discovered that the tower had says John. “There was a quote from probably begun to lean from day one. the mayor saying ‘It’s in the Piazza “You can see tapered layers of ma- dei Miracoli [the Square of Miracles], sonry, showing that the builders were Image courtesy of John Burland trying to correct the slant even as they Image courtesy of tiseb / Flickr were building it,” says John. The Leaning Tower He and other technical experts spent of Pisa, pictured two years trying to understand why before John’s the tower was leaning and what was work on it began, controlling its movements, which was is surrounded by absolutely fundamental to solving mythology. the problem, John believes. “Up until then, people had just proposed solu- tions at random, but until you really understand things, you’re likely to get it wrong.” They discovered that the leaning The Leaning Tower of Pisa, after John’s was caused by a combination of the work, is still leaning, but more stable.