Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Perfect Pisa - a tall order

Pisa; Leaning tower; After a decade of worrying, discussion, argument and testing, work to permanently stabilise Italy's historic leaning tower of Pisa is moving ahead at last.

When Professor John Burland of Imperial College London's soil mechanics department first got involved with work to save the near-toppling tower at Pisa in 1990, he walked into a minefield of politics and scare mongering.

Ten years later, he is pleased to say that criticisms and bureaucracy are showing signs of subsiding. Under his direction, the once ever-toppling landmark has been pulled back from the brink of collapse to the tilt it was at in 1969.

Getting the tilt back to this point was the result of preliminary tests of a method which involves undermining the north side of the tower. Burland now hopes permanent stabilisation work can start next month using the same method more extensively.

Official blessing for the venture came last week when Burland and the other members of the 14-strong international commission set up to save the tower were joined on site by Italian construction minister Villier Bordon.

He underlined his government's commitment to press ahead with the stabilisation project and pledged around £2.3M to see the work through 2001. It is possible that this year's work could lead to the tower reopening to the public by mid-2001.So it is now full steam ahead with the main plan to rotate the tower to a safer degree of lean. The target is to move the top 500mm to the north and reduce the stress on the ancient marble masonry by around 10%. With 45mm already achieved in the trial work - an eight-fold increase on the original target - things are looking good.

Though confident, Burland remains cautious about the success so far and points out that this is not a project to rush - there are no second chances if anything goes wrong.

The tower, which took 177 years to build between 1173 and 1350, will collapse in seconds if anything goes wrong.

The tower sits on soft clayey and sandy silt over a thicker layer of highly compressible Pancone Clay at a depth of 10-25m. This in turn rests on a layer of denser sand. Compression of the ground and fluctuations in the water table are thought to be the main causes of settlement.

'The preliminary excavation was utterly terrifying at the start,' says Burland, reflecting on the first results sent back from site. 'I looked at them and thought 'Oh my God, it is going the wrong way'.' This glitch turned out to be the result of seasonal temperature variation and the northward trend continued.

But Burland also admits to being more than a little frustrated by the pace at which the project has moved and the frequency of political interference.

The tower commission was formed in March 1990 just months after the tower was closed to the public due to fears about its safety. Burland proposed the soil extraction technique for stabilising the tower and convinced the Commission that it was the best way forward.

The first precaution was to load the north side of the tower's foundations with 600 tonnes of lead weights to temporarily pull the tower back from the brink and gain time to carry out the permanent works.

The weights were to be replaced by a ring beam and ground anchors, but there was a setback in 'black September' 1995. The Government-appointed contractor, a consortium of Bonifica, Ismus, Italsonda, Rodio and Trevi, hired to carry out the stabilisation work, found the foundations were not as reported.

The tower subsequently lurched south, causing hearts to flutter until ground freezing and more lead saved the day, albeit temporarily (NCE 12 October 1995).

With this technical problem resolved and the soil extraction plans making progress on a specially constructed test tower, politics again took over in 1996. By then, the commission's jurisdiction had run out and the team was disbanded, halting work.

A new committee including eight of the original members was imposed by the Italian government in early 1997. It had to wait six months before holding its first meeting.

'There was quite a lot of antagonism towards the old commission which meant we had to represent the arguments for using the soil extraction method right from the beginning again,' Burland explains. 'As the commission did not meet until June 1997, it took until around August 1998 to get the preliminary soil extraction trial agreed.'

Legal problems again raised their head as the commission's jurisdiction ran out once more at the end of 1998.

However, the preliminary work had been agreed and so with cable stays attached to the tower as a precaution, it went ahead with contractors and consultants working for nothing on a promise of future payment.

Burland admits that the preliminary trial had the advantage of selling the method to the commission and to bystanders who continue to offer their own views on how to save the tower.

'It is pleasing to see that there has been a shift in the opposition to what we are doing,' says Burland, reflecting on the outcome. 'People are still critical but at least they are now saying 'why didn't you do this sooner?' '

But although about £15M has already been spent over the last decade, Burland is first to acknowledge that the real work is only just beginning. 'Certainly, the preliminary work has been a success but we still have a big job to do,' he points out. 'There is no point in raising the flag when you are just one foot up Everest.'

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.