The leaning tower of Pisa has stopped moving for the first time in its 800 year history.
Last month, the Pisa authorities announced that La Torre had
not shifted a single millimetre for four months. This was a result of underground work carried out over the past year under the direction of a committee of 13 Italian and foreign experts, which had brought the tower slightly back towards the vertical.
At least part of the credit must go to John Burland, professor of soil mechanics at Imperial College, London, who has worked on the tower since 1990, when the first successful programme to stabilise the landmark began.
"I got a phone call from Pisa and was simply told my name was on the list," he said. "I wasn't asked, I was told. I'd never even been to Pisa.
"When I did go there, I turned a corner and suddenly saw this amazing, impossibly leaning tower looming over me. I had
serious qualms about what I
was about. My first reaction was 'It shouldn't be standing, but it is'," Professor Burland said.
Initially, 600 tonnes of lead were placed at the base of the tower on the "uphill" side. Then 50 pipes were driven into the ground beneath to slowly extract earth. The simple-sounding process took several years.
A second excavation phase is about to begin, and the remaining ballast will be taken away gradually.
"We had to work very, very gingerly," explained Professor Burland. "This is a unique monument, still standing after 800 years, on the point of falling over and exploding. It is an absolute fluke that it is still standing, so it was an extremely sensitive project. One would not like to be remembered as the engineer who destroyed the leaning tower of Pisa."
Professor Burland combined his work on the tower with teaching at Imperial College. "I've used the tower project in my lectures, and much of the computer analysis is being done with the students."
Over the past year, the tower has been brought back towards the vertical by 4.5cm, and between November and February it did not move.
"We are now planning to
bring it back up by another
45cm, and then stabilise it
permanently," said Professor Burland.