Why Did The Tower Of Pisa Start To Lean

Question

What went wrong with the leaning tower of Pisa, and how were these problems remedied?

Answer

Construction of the Tower of Pisa began in 1173, a time when little consideration was given to geotechnical engineering. As such, the tower was constructed with inadequate foundations, over a varying water table, on soil that would undergo large amounts of differential settlement. The construction was staggered over the course of 200 years due to various distractions, resulting in inactivity that benefited the structure, allowing time for the ground beneath the tower to settle between builds. Whenever construction recommenced, the tilt of the tower was more noticeable and successive floors were completed slightly taller on the sinking side, in an attempt to compensate for the tilt. This resulted in the tower’s distinctive curved shape on completion in 1360.

The tower continued to settle, and in the early 20th century was found to be sinking by 0.05 inches per year. A number of attempts were made throughout the 20th century to stabilise the tower, without significantly decreasing the tilt, which was an important aspect of this tourist attraction. In 1990 the tower was closed to the public and it was eventually decided that the best method for stabilising the tower would be to replace the soil under the higher side of the tower, allowing this to settle further down, thus decreasing the tilt to a safe, but still noticeable, angle.

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