Experts have been arguing about the reason why the leaning tower of Pisa leans. Especially in the14th century, people are wandering between two kinds of arguments, whether the leaning tower of Pisa is the result of the unpredictable and inevitable cumulative effect of land subsidence during the construction process, or whether the architect deliberately did it. In the 20th century, with the more and more accurate measurement of the leaning tower of Pisa, the in-depth investigation of foundation soil by various advanced equipment and the study of historical archives, some facts gradually surfaced: the leaning tower of Pisa should have been a vertical building at the initial design, but it began to deviate from the correct position at the initial stage of construction.
The leaning tower of Pisa is inclined because of the particularity of the soil layer under its foundation. Under the leaning tower of Pisa, there are several layers of soil with different materials. All kinds of soft silt and extremely soft clay deposits are alternately formed, and the groundwater layer is about one meter deep. This conclusion is obtained after observing the composition of foundation soil. The latest excavation shows that the bell tower was built on the edge of the ancient coast, so the soil was desertified and sank when it was built.
According to the existing written records, the leaning tower of Pisa has been slowly tilting for centuries, and has actually reached a certain degree of balance with the soil under the foundation. At the end of the third floor of the first stage construction, the bell tower leans about 1/4 to the north. In the second stage, due to excessive rectification, the seventh floor of 1278 tilted about 0.6 to the south, and it increased to 1.6 when the top-floor clock house was built in 1360. 18 17, two British scholars, Crecy and Taylor, measured the inclination with a plumb line, and the result at that time was 5. 1550 giorgio vasari survey and 18 17 Crecy and Taylor survey were 267 years apart, and the dip angle only increased by 5 cm. Therefore, people have not carried out special maintenance on the leaning tower.
However, a project of 1838 led to the sudden acceleration of the leaning tower of Pisa, and people had to take emergency maintenance measures. At that time, architect Alessandro della Gherardesca excavated around the original sealed leaning tower foundation to explore the shape of the foundation and reveal whether the cylindrical foundation and foundation steps were the same as expected. This behavior made the leaning tower lose its original balance, and the foundation began to crack. The most serious phenomenon was the influx of groundwater. The survey results after this project show that the tilt has increased by 20 cm, while the total tilt in the previous 267 years was only 5 cm.
After the completion of the project of 1838, the accelerated inclination of the leaning tower of Pisa lasted for several years, then stabilized and decreased to about 1mm per year. Now the tower has deviated from the "natural posture" by more than 5 meters.