Saturday, February 19, 2011

Leaning Tower of Pisa- mystery solved

Professor John Burland has spent the last two decades striving to save and understand the Leaning Tower of Pisa. After defying gravity, Italian bureaucracy and accusations of corruption, it seems he’s finally solved the 800-year mystery. Pisa lies on a thin layer of soft alluvial silt, above a thick layer of even softer marine clay. The tower has tilted pretty much since day one and down the centuries proud Pisans have proclaimed only God was holding it up, out of love for their city. The name Piazza dei Miracoli seemed apt.

In the 19th century alone the tower crept southwards by a metre. Investigations were held throughout the 20th century – 16 different committees were appointed, of which Burland’s was the last – but nobody could work out what was causing the inclination. If the soil was uniformly unstable, why should the tower lean south rather than north? On the night of September 7 1995, the tower lurched southwards by more than it had done in the entire previous year. Burland was summoned for an emergency committee meeting, and Ladbrokes were offering 11-4 odds the tower wouldn’t survive into the 21st century. ‘We really were within days of losing it,’ Burland says. The anchor plan was immediately abandoned and another 300 tons of lead ingots added.

Soil extraction activity delayed a collapse by centuries, but never actually halted the leaning, Burland later oversaw a permanent solution, too. Via his data analysis, Burland unlocked the 800-year mystery as to why the tower leans south not north: namely, a fluctuating water-table on the upper layer of silt. By a quirk of local geography, Pisa’s water-table rose higher on the tower’s north side, often reaching within one foot in rainy season and this gave the tower an annual ratchet southward. Armed with this vital information, in 2003, Burland introduced a new drainage system beneath the piazza’s north side, one that lowered and stabilised the water-table, so there’s no kick in either direction. Problem solved. 

The inclination continues to be monitored daily by the OPP and new figures reveal that the tower didn’t move at all between 2003 and 2009. ‘It’s stopped leaning completely. After soil extraction and now the water-table stabilisation, the tower is safer than ever,’ says Burland with a mixture of pride and relief. 

The Pisans, though, are a hard people to please. Some accuse Burland et al of sterilising their tower - for, part of its old mystique had been the possibility it might collapse at any moment, the frisson that a voyeuristic visitor might witness such a fall. ‘You can’t please all of the people all of the time,’ Burland shrugs.

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