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The Not-so-Leaning Tower of Pisa

So, it was good to see the news last week that the leaning tower of Pisa is leaning just a little less than it was, and is therefore less likely to fall over. The thought did cross my mind, though, that it would be an awful pity if the wonders of modern engineering that were used to halt its slow fall went so far as to as to straighten it up altogether.

Apparently some calculations show that that could happen by the year 2300, at the current rate of movement. But we need not worry. The tower can't ever be made fully upright because it is not just leaning, its also crooked - deliberately so!

I'd forgotten about this, but re-read it last week.

When work began in 1170, the porous clay (under the south side) almost immediately became evident and the project was abandoned for 90 years with only 3 stories built. But they started work again in 1270 with an ingenious plan to tackle the problem: they built the remaining floors at an angle to the base, hoping that they could thus offset the lean. I love this. I have tried similar things in my efforts at household maintenance. And usually with similar results - which is to say almost total failure. Because when it was finished the tower was still leaning. As little as 1.3 degrees from the vertical in its early years, but that grew steadily to as much as 5.4 degrees by the early 90s. It wasn't so much leaning, as (very) slowly falling.

If I have it right, the remedial work had many strands but mainly involved undermining the more solid foundations to the North, so that that side of the tower would sink enough to offset the sinking to the South. It seems to have worked because the lean is now only 3.97 degrees.

The slant built into the structure to offset the lean seems only barely visible to me, but presumably it was enough to make it seem somewhat straight in 1372 when it was finally finished.

But its good to know that it's there, ensuring the leaning tower will always lean. Even if its fixed.

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