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NOVA: In your opinion, will the tower remain standing indefinitely, or is it
still liable to sudden collapse even, say, after the full intervention?
Burland: As far as the foundations are concerned, I'm satisfied that the tower
would not be liable to sudden collapse anymore. I think we will have done
enough to stabilize the tower permanently. By reducing the inclination of the
tower, we've reduced the forces in the masonry, and we're also doing some
strengthening. I don't think anyone could do more than we have done, but the
masonry remains uncertain. We don't know exactly how strong it is. I think that
if the tower were going to go, that's where the weakness would be, though it
would probably require a pretty major earthquake or quite significant
deterioration in the masonry itself for a major collapse to take
NOVA: So it's never been a case of the tower actually tipping over? It's more
of a downward collapse?
Burland: Actually, when we first came on the job, there was a danger of it
tipping over, because the tower was accelerating. I think we've pulled back
from that problem. We've already brought the tower back to where it was in
1970, and all the indications are that soil extraction will continue to be
NOVA: Does it surprise you that the tower has stood so long on such a weak
Burland: Yes, it does, because the tower has had at least three very narrow
escapes. The original builders stopped building it about eight years after they
started and left it for 100 years, and we know that if they hadn't stopped, it
would certainly have fallen over. They didn't know that; it was a complete
fluke that they stopped, really. And they stopped again very near the top—again, for some unknown reason. If they hadn't, there's no question that it
would have fallen over.
NOVA: Because the soft soil hadn't had time to compact?
Burland: That's right. Then in 1838, an architect dug a trench around the base
of the tower so that the people could see the foundations and the bottom of the
columns, which had become buried as the tower subsided. Over a few days that
year, the tower lurched about half a degree, or half a meter or so. It must
have been terrifying. How it didn't fall over, nobody knows.
Burland says that most suggestions for how to straighten
the tower would "have it over" while implementing the ideas.
NOVA: Have you heard of any hot, new, viable suggestions for how to preserve
Burland: Not recently, no. We've still got the Chinese engineer who claims that
he's straightened 80 pagodas, though he never told us what his method is, and
we keep getting various other suggestions. The problem with almost all the
suggestions is that they're probably viable—if only you could implement
them. But all of them would have the tower over while you were trying to
implement them, and that's always been the big problem: finding a method that
you can implement without destabilizing the tower.
The ultimate goal is to reopen
the Leaning Tower to tourists, who have been unable to ascend the tower since
its closing in 1990.
NOVA: As an expert in soil mechanics, have you been called on to help save
other historic and/or modern buildings?
Burland: I've been involved in quite a number of historic buildings. I suppose
the two with which I've been most involved are, first of all, the Metropolitan
Cathedral in Mexico City, which has undergone enormous differential settlements
due to pumping water out from very low down in what is a very soft, volcanic
lake bed. The cathedral has settled differentially by about two-and-a-half
meters. We used this process of under-excavation there to straighten the
Cathedral out, to reduce the kinks and deflections in it, and it's been very
My life seems to be plagued by towers, because the other big project I've been
involved in over the last few years has been insuring the stability of the Big
Ben clock tower during the construction of an underground railway alongside it.
There we did the reverse of what we're doing at Pisa; we pumped grout into the
ground. Every time Big Ben tilted a little bit, we pumped grout in and stopped
it leaning. We could do that because the ground in London is much stronger than
it is in Pisa. We wouldn't dare do that at Pisa; that would probably have the
NOVA: Now if you achieve your half meter in the full intervention, will the
tower then be open to the public?
Burland: That's the intention, to reopen the tower. I'm sure that millions of
people will come, and hopefully what we've done will have actually added to the
enigma of the whole structure. At the same time, it's very important that we
don't relax and become complacent, because there's a long way to go, and we've
got to be very, very vigilant.