阅读理解
The Leaning Tower of Pisa was straight like a pole when the construction began in 1173. It started to shift direction soon after construction because of poor foundation in addition to the loose layer of subsoil(底土). At the beginning, it leaned to the southeast before the shaky foundation started to shift leaning towards the southwest. After the period of structural strengthening at the beginning of the 21st century, now the Leaning Tower of Pisa leans at an angle of 3.97 degrees.
In 1178, the shift in direction was observed for the first time when the construction had progressed further to the third floor. The tower was heavy for the three-meter foundation that was built on a weak area of land.
For compensating(补偿) the leaning position, the builders started to construct the upper floors with one side higher than the other one. This caused the tower to lean in the other direction. This unusual structure led to the tower being actually curved. In spite of these efforts, the tower kept on leaning.
The government of Italy started to plan prevention of the complete collapse of the tower in 1964. However, a request was put forward by the authorities to keep the leaning position because of the tourism industry of the region.
After nearly two decades of careful planning by engineers, historians and mathematicians, the stabilization efforts for the Leaning Tower of Pisa started in 1990. The tower was closed for the general public and the people living nearby moved away. For reducing the total weight of the tower, its seven bells which represented the seven musical notes were removed. The tower was reopened for the general public on December 15, 2001.
In May 2008, after removing another 70 metric tons of earth, the engineers announced that the tower had been finally stabilized and it would remain stable for at least 200 years.
