Twenty-seven years ago today, on July 30, 1998 (June 8, 1998 lunar calendar), Cao Shizhong participated in the rescue of the Leaning Tower of Pisa. The world-famous Leaning Tower of Pisa was invited to Italy on July 30, 1998. Cao Shizhong, a Chinese expert who made suggestions for saving the Leaning Tower of Pisa, told reporters in Pisa on the 30th that he was "more confident and more confident" in saving the tower after on-site inspection. Cao Shizhong, an expert in the correction and reinforcement of Chinese buildings, believes that the internal and external conditions of the Tower of Pisa and its environment are better than he originally thought. He said that using the "correction method of the tilted ancient tower" he invented, he is sure to save the Leaning Tower of Pisa within 10 months. According to Cao Shizhong, his rescue plan is to "adopt a comprehensive management method that combines structural reinforcement, weight reduction, and the tower body and foundation." Cao Shizhong arrived in Rome on the 28th at the invitation of the Italian-Chinese Friendship Association Mr. Ranciotti. During his stay in Italy, he will discuss a series of issues related to saving the Leaning Tower of Pisa with relevant Italian parties, especially the Leaning Tower of Pisa Rescue Work Committee. Cao Shizhong said that "saving the Leaning Tower of Pisa is the biggest long-cherished wish in my life". Partial Extension of the Leaning Tower of Pisa: The Secret of the Leaning Tower of Pisa for a thousand years Extended Reading: The Secret of the Leaning Tower of Pisa for a thousand years The Leaning Tower of Pisa is undoubtedly an important building in the history of architecture. It is the independent bell tower of the cathedral of Pisa, Italy. It is located on the Miracle Square in the north of Pisa, Tuscany Province, Italy. The large lawn of the square is scattered with a group of religious buildings. They are the cathedral, the baptismal, the bell tower and the cemetery. They are all made of milky white marble. They are relatively independent but form a unified Romanesque architectural style. The Leaning Tower of Pisa is located behind the Cathedral of Pisa. The Leaning Tower of Pisa is 58.36 meters high from the foundation to the top of the tower, and 55 meters high from the ground to the top of the tower. The width of the bell tower wall on the ground is 4.09 meters, and it is 2.48 meters wide at the top of the tower. The total weight is about 14,453 tons. The center of gravity is 22.6 meters above The circular foundation covers an area of 285 square meters, and the average pressure on the ground is 497 kPa. The tilt is about 10%, or 5.5 degrees, 2.3 meters away from the outer edge of the foundation, and the top layer protrudes 4.5 meters. The tilt was first discovered in 1173. Why not? Experts have conducted a full study of the entire history of the Leaning Tower of Pisa, as well as the building materials, structure, geology, water sources, etc., and tested it with various advanced instruments and equipment. After research, Professor Pilodi, a medieval historian of Pisa, believes that each stone brick used to build the tower is a stone carving masterpiece. The bonding between the stone bricks and the stone bricks is extremely ingenious, which effectively prevents the fracture caused by the tilt of the tower and becomes a factor that prevents the leaning tower from falling. But he still emphasizes that the top priority is to figure out the mystery of the leaning tower of Pisa. Professor Gehry, an expert on the observation of the tower, based on the speed of the Leaning Tower of Pisa's tilt in recent years, speculated that the Leaning Tower of Pisa will collapse in 250 years because the center of gravity of the tower exceeds the outer edge of the tower base. But the relevant personnel of the Leaning Tower Service of Pisa of the Ministry of Public Affairs have refuted Professor Gehry's view, arguing that it is unreliable to calculate only by mathematical methods, and that the Leaning Tower of Pisa is "a comprehensive problem intertwined with multiple facts." Other researchers have investigated and found that the Leaning Tower of Pisa once tilted to the east and then turned to the south. They also believe that the tower has tilted and will not fall in the past few hundred years, and whether it will not fall in 250 years may not be limited to simple assumptions and predictions. Of course, the people of Pisa are most concerned about the fate of the leaning tower. Although they are also worried about the leaning of the leaning tower, they are more proud and proud of their hometown to have a leaning tower that they think is comparable to the famous buildings in the world. They firmly believe that it will not fall, and they have a saying that the tower of Pisa is as strong and sturdy as the Pizzans and will never fall. They are most disgusted by suggestions to rectify the leaning tower. For example, in 1934, 90 tons of cement were sprayed on and around the foundation, and the foundation was waterproofed. Instead, the tower became more unstable, moved around, and tilted faster. The reason for the tilt was once thought that the bell tower was deliberately designed to tilt, but this is not the case. As the bell tower of Pisa Cathedral, when construction began on August 9, 1173, it was designed to stand vertically. It was originally designed to be eight stories and 54.8 meters high. Its unique white shimmering medieval style building, even if it did not tilt later, would be one of the most noteworthy bell towers in Europe. Experts have debated why the Leaning Tower of Pisa leans. Especially in the 14th century, people were torn between two theories. Whether the Leaning Tower of Pisa was the result of the cumulative effect of ground sinking that could not have been predicted and avoided during construction, or whether it was intentional by architects. In the 20th century, with the increasingly accurate measurement of the Leaning Tower of Pisa, the use of various advanced equipment to conduct in-depth surveys of the ground layer, and the study of historical archives, some facts gradually emerged: the Leaning Tower of Pisa was originally designed to be a vertical building, but it began to deviate from the correct position in the early days of construction. In 1178, when the bell tower was built to the fourth floor, it was found that the bell tower had been tilted to the southeast due to uneven foundation and soft soil, so the work was suspended. In 1198, the existence of a bell ring in the bell tower was recorded, which marked that although the bell tower was tilted, at least one bell was hung, fulfilling its original intention as a bell tower. In 1231, work continued, and the first recorded use of marble in the bell tower. The builders took various measures to correct the tilt, deliberately building the upper part of the bell tower into an opposite tilt in order to compensate for the deviation of the center of gravity that had occurred. By the time it reached the 7th floor in 1278, the tower was no longer straight, but concave. Work was suspended again. In 1292, Giovanniano Pisano measured the tilt of the bell tower with a plumb line. Slow tilt According to existing written records, the tilt of the Leaning Tower of Pisa over the centuries was slow, and it and the soil layer below its foundation actually reached some degree of balance. At the end of the third floor of the first phase of construction, the clock tower was tilted about 1/4 ° to the north. In the second stage, due to excessive correction, the seventh floor was instead tilted to the south by about 0.6 ° when it was completed in 1278. It was increased to 1.6 ° when the top bell house was built in 1360. In 1817, two English scholars, Cresy and Taylor, measured the tilt with a plumb line, and the result was 5 °. The tilt increased by only 5 centimeters after 267 years between Giorgio Vasari's survey in 1550 and Cresy and Taylor's survey in 1817. Therefore, no deliberate repairs were made to the leaning tower. In 1360, after almost a century of stagnation, the bell tower began its final sprint towards completion and made the last important correction. The top floor of the placed clock was completed in 1372. The eight-story bell tower, 54 meters high, has seven bells, but the bell tower never rang because it was always in danger of collapsing. And it has been continuously tilting downward. The reason why the Leaning Tower of Pisa leans is due to the particularity of the soil layer below its foundation. Under the Leaning Tower of Pisa are several layers of soil of different materials, formed by sediments of various soft silts and very soft clay, and at a depth of about one meter is the groundwater layer. This conclusion was reached after observing the composition of the ground soil layer. The latest excavations show that the bell tower was built on the edge of the ancient coast, so the soil was already sandy and sinking when it was built. Accelerated tilt However, a project in 1838 caused the Leaning Tower of Pisa to suddenly accelerate its tilt, and emergency maintenance measures had to be taken. At that time, the architects AlessandrodellaGherardesca excavated around the originally sealed foundation of the leaning tower to explore the shape of the foundation, revealing whether the cylindrical column bases and foundation steps were the same as envisaged. This behavior caused the leaning tower to lose its original balance, the foundation began to crack, and most seriously, the influx of groundwater occurred. The survey results after this project showed that the tilt had increased by 20 centimeters, compared with the previous 267 years. After the completion of the project in 1838, the accelerated tilt of the Leaning Tower of Pisa continued for several years, and then leveled off, reducing the tilt to about 0.1 centimeters per year, and the tower was more than 5 meters away from its "natural position". Saving the Leaning Tower The Italian government closed the leaning tower in 1990 and began a £25 million restoration project, including strengthening the foundation and draining groundwater, and supporting the tower with steel cables. The restoration project was completed in 2001, and the leaning tower was immediately straightened by nearly 38 centimeters. The Leaning Tower of Pisa in Italy has finally stopped its tilt. The latest survey found that the tilt of the tower decreased by 2.5 centimeters between 2001 and 2013. This is undoubtedly good news for the protection of this world cultural heritage. Tips Transportation: Pisa can be reached in about 1 hour by train or car from Florence. Accommodation: Since the tourist attractions of the ancient city of Pisa are relatively concentrated and can be visited in half a day, it is recommended to stay in Florence. Special reminder: The Leaning Tower of Pisa is open for a limited time every day, usually limited to 20 people each time, the tour time is 30 minutes, and the ticket price is 13 euros per person.