I recently traveled to Italy and as a Structural engineer I found Pisa tower very interesting. The Tower of Pisa (Torre di Pisa) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa, known worldwide for its unintended tilt. The tower's tilt began during construction, caused by an inadequate foundation on ground too soft on one side to properly support the structure's weight. The tilt increased in the decades before the structure was completed, and gradually increased until the structure was stabilized (and the tilt partially corrected) by efforts in the late 20th and early 21st centuries.
It looks like the leaning Tower of Pisa will keep on leaning, stably, awhile longer. More than dozen years after major foundation work, the imperfect edifice hasn’t increased its lean. In fact, civil engineer John Burland of Imperial College London says his international team has succeeded in straightening the marble bell tower by 19 inches, reducing its angle of incline by about 10 percent, and slowing its once steady creep to nearly nothing.
It wasn’t easy. Built from 1173 to 1370 on silt and clay, the eight-story, 182 foot-tall tower resisted many efforts to stabilize it. What finally worked was a soil-removal process called under-excavation and the addition of wells to regulate groundwater. The chief fear now? A big earthquake. "Absent that," says Burland, "I'd be very surprised indeed if we see it lean significantly again."