Only the Most Ingenious Engineering Skill Can Save This World-Famous Building from Collapse
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| Only the Most Ingenious Engineering Skill Can Save This World-Famous Building from Collapse |
THE DEAR old lady of Pisa - a name the citizens have for their Leaning Tower - is a
very sick old lady, and any day now she could totter and fall. The world's most famous tower has leaned for 800 years without mishap, but even miracles must come to an end. Each year it leans a little more.
Italian scientists hover over the invalid to record its pains and stresses. There are seven bells at the top of the tower, one of which weighs three and a half tons. Once they rang out tolling for the dead and the victorious alive. The scientists forbade the ringing. Too much vibration. Lorries and motor scooters are not allowed in the area for the same reason. Each June 19 since 1911, at five o'clock in the morning, a professor from the University of Pisa has taken a precise measurement of the slant of the tower. The saddening report is always the same: the tower has leaned a fraction of an inch more. Last year the 175-foot-high tower was heeling over an incredible 14 feet 10 inches out of the perpendicular on its south, or leaning, side. The tower foundations were laid in 1173 by the famous architect and builder Bonanno Pisano, who worked on it until 1185, when he vanished, leaving the structure only three and a half floors high. Whether he stopped because he saw to his horror that his tower was slanting, or whether he died, the records do not say. It stood like that, half-finished, for 90 years until a second architect tried his hand. He should have torn down the tower, deepened and widened the foundation and started all over again. Instead, he added three and a half circular tiers, trying to adjust it by straightening the floors of the fifth, sixth and seventh tiers to compensate for the tower's inclination. Some 80 years later a third architect completed the tower with a domed eighth floor, to house the bells. It had taken almost two centuries to build - and still it leaned. Some people have claimed that Bonanno put the lean into his tower deliberately, in order to astonish the world, especially Pisa's rival, Florence. The real explanation of the tilt, however, lies in the unstable subsoil of Pisa which is a sponge of alluvial clay and sand, 60-per-cent water. In fact, the foundation is in an old lagoon in which tide lines can be traced. Though the Leaning Tower's massive ground-floor walls are more than 13 feet thick, they are not enough to offset the shallow, nine-foot-deep foundation and the sinking earth beneath it. From every Country of the world people Come dashing with ideas to keep the tower alive. An entire wall of the Ministry of Public Works in Rome is occupied by shelves filled with their plans. Run water pipes into the foundation and freeze it, one rescuer says. Haul it straight with teo locomotives, says another. An RAF pilot proposes holding it in place with barrage balloons. Several have suggested taking the structure apart piece by piece and rebuilding it. One man, a German, actually tried to put his scheme into practice. Accompanied by friends in a roistering mood, he slung a cable round the tower and shackled it to his car. Then he stepped on the starter and moved off smartly - minus the tower and minus his bumper. The only way to strengthen the tower so that it will stand Łor another millennium is to remake the Łoundation. Pumping cement into the existing one is not enough; it was tried once without success. A means must be Łound to keep the 14,500-ton tower intact while new foundations are built. The operation would be extremely delicate, for the monument is fragile. A small mistake would leave nothing but a confetti of stone. Several Italian engineers have detailed plans for the job, which are being studied by a special committee set up by the Ministry of Public Works. One plan, by Gustavo Colonnetti, honorary proŁessor of the University of Pisa, proposes placing round the tower 15 enormous jacks - each one with its own independent foundation and each one capable of lifting 1,000 tons. Cables from the jacks would be fastened to a concrete hoop round the tower's base. The operation would begin in earnest with the slow raising of the tower . A few millimetres would suffice. Once there was clearance, the work of laying a broad, deep foundation would begin. |
Professor Silvio Ballarin of the University of Pisa checks the angle of the tower |
With variations, this is roughly the plan of another noted engineer, Letterio Donato. His suggestion: erect on the north side of the tower two high steel structures bound to it by cables to keep the building and all its columns intact. Then build underground, all round the foundations, eight concrete caissons, and with the help of 16 jacks transfer the weight of the tower from the foundations to the caissons.
Any of the proposed plans would cost a great deal of money. In none of the plans is there any desire to straighten the tower; only to reinforce it so that it may continue to lean with safety. Apart from the engineers, few Italians seem much concerned with the safety of the tower, certainly not the citizens of Pisa who sing: "The tower leans and leans and leans but it will never fall down." |
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This may be rosy optimism but it is justified by the simple fact that during the war the town quaked with 1,000 bombs dropped by Allied planes. Shell fragments nicked the tower, but the stability (or in- stability) of the structure was not affected. It has also survived more than 100 seismic shocks and two serious attempts to strengthen the foundation. In each attempt the only result was to exaggerate the lean. The townspeople were gleeful. This was confirmation of their belief that their tower is immortal. As for the tourists, they are understandably a trifle nervous. They park their cars away from the tilt, and when they come down after their ascent they hasten away in a small flurry of excitement as if they had accomplished a daring feat. Each year three million people visit Pisa. Most of them stop only for a quick look at the tower and to take a Łew photographs. About 600,000 spend the night in town, and 120,000 pay the admission fee and climb the 294 steps to the top. All told, the tourist takings are not less than $350,000 annually. This may be why tourist officials in Pisa do not relish the thought of changing the tower, and the tradesmen agree with them, heart, soul and cash register. If the tower is made safe, they feel, tourists might cease coming; its instability - and possible collapse - is its greatest attraction. But if nothing is done soon, the tower will collapse. It may fall tonight, it may not fall for 50 years or more, but fall it will. And when it does, a strange and beautiful thing will have gone from the world. |
