Leaning Tower of Pisa

1. Construction time : 1173 - about 1370
2. Location: Pisa, Italy

Leaning tower rising high Putti Nozzle, with a group of three putti holding Pisa's badge, the work of Giusepe Vaccà, 1764

Imagine a tower built with soft materials like rubber foam, with a slow and steady tilt that gradually increases to the point of collapse. The tower building blocks are so fragile that the stress created by increasing tilt is approaching the limit of material durability - it can explode at any time . The disturbance arising from the spraying of mortar or temporary support of the wall to reinforce the footing of the edge protruding out will cause the tower to fall, while the support by cable or pull by cable will cause a collapse. pour of masonry. This is the exact image of the limited status of Pisa Leaning Tower , with stability demonstrating the highest level of construction engineering challenges.

Pisa leaning tower is not only a place to attract some cranky visitors, but the tower is an architectural pearl and is always one of the most important memorial works of medieval Europe even though the tower does not tilt. . Located in Piazza del Duomo, the tower is only a part of a complex of 4 important white-white buildings, including a cathedral (Duomo), a bell tower (campanile - leaning tower), Baptism hall and cemetery ( Camposanto). Like other buildings in Piazza, the bell tower intends to show the prosperity and glory of the prosperous state of Pisa, so the new tower has such unique and mysterious beauty.

Construction details

The tower consists of 8 floors, 58.4m high; weight of 14,500 tons; foundation block with a diameter of 19.6m; with a maximum depth of 5.5m below the ground elevation. The foundation is inclined southward 5.5 degrees from the horizontal, so the 7th floor protrudes 4.5m above the first floor. The building is in the shape of a hollow cylinder with rows of columns surrounded. The inner and outer surfaces of the cylinders are marble-clad in a very tight joint, but the material between these outer layers is only mortar and stone, so there are many large pores inside. A spiral staircase leads to the top of the tower located inside the wall.

Scene of Pisa cathedral, along with the leaning tower behind

The lower layer consists of three distinct classes. Class A is about 10 meters thick, consisting of a loose, muddy sediment layer under a shallow water area less than 10,000 years ago. Class B is a weak, porous, marine clay beneath 30,000 years ago, up to 40m deep. Class C is solid sand with considerable depth. Groundwater is located in Class A with depth from 1m and 2m. Many boreholes around the ground and even below, the tower shows that the surface of Class B is disc-shaped due to the weight of the upper tower, which can infer the average settlement of the tower from 2.5 - 3m, showing how low the soil below can be compressed.

Actual data:

1. 

   The leaning tower chart shows an increasing inclination through the construction stages.

   Height from foot of foot to bell tower: 58.4m
2. Foot diameter: 19.6m
3. Tower weight: 14,500 tons
4. Starting construction of foundation foot: August 9, 1173
5. Postponed work on the 4th floor: around 1178
6. Constructed to a ladder-shaped decorative smoke (on the 7th floor): around 1272-1278
7. Completed bell tower: about 1370
8. Dig a walk around the base of the tower: in 1838
9. Tower tilted to the south: 5.5 degrees
10. Subsidence of foot nails: about 3m

Construction history

The tower started construction on August 9, 1173 under the control of Bonanno Pisano. Around 1178, when it was built to the fourth floor, it was halted. The reason is still unclear, but the work with much more strenuous effort in Class B may not be enough to withstand the load and the tower seems to be tilted. After a pause of nearly 100 years, Giovanni di Simone proposed to build around 1272, over this time the clay intensity increased due to the reinforcement by the weight of the tower. Around 1278, it was halted until the seventh floor (the cause was probably due to civil war). Certainly the tower that was completed during this period was tilted. Around 1360, when the reinforcement of the clay layer began, Tommaso Pisano began construction on the bell tower completed in 1370 - almost 200 years after the commencement.

The tower must tilt when starting to build the bell tower, but it is worth noting that the bell tower is more vertical than the rest of the tower. On the south side, there are 6 steps on the decorative floating block on the 7th floor, leading to the floor of the bell tower, while there are only 4 steps on the northern side.

Inclined process

There is evidence that the inclination has started right after building the tower - the tower axis is not vertical but leaning towards the North. In a straightening effort, the smaller masonry blocks are used at the elevation of each floor to straighten the tower axis. By analyzing the relative tilt of the masonry layers, the tilting process of the tower is evident. At the end of the first phase, the tower is tilted to the north about 1/4 degree. At that time, when the construction went to the fourth floor, the tower began to tilt south, to the point that in 1278 when it was built to the 7th floor, the tower tilted southward about 0.6 degrees. By 1360, the inclination increased to 1.6 degrees.

Advanced computer analysis showed that the tilt increased rapidly when built to the 7th floor and when added to the bell tower, it was built like a brick tower pressed on a porous carpet. Temporary safety cable connection on the 3rd floor Can be built to a certain allowable height, but not higher, no matter how carefully built. The tower is only at its allowable height and is very close to the safety limit.

In 1817, two British architects used plumb lines to measure the inclination and found that at this time the tower was tilted to 5 degrees. In 1838, architect Alessandro della Gherardesca dug a walkway around the foundation of the tower to reveal the columns and steps of the original foundation before the settlement. As a result, the water rushes to the south side, because the earthworks are below the water table. There is also evidence that at this time the tilt of the tower increased significantly by almost half a degree, about 5.4 degrees.

Accurate measurements began in 1911, indicating that the tilt of the tower kept increasing every year, and after the mid-1930s, the inclination doubled. In 1990, the inclination was like a horizontal shift at the top of about 1.5 mm per year. In addition, all impacts in the tower are due to the tilt of the tower as more and more tilt. For example, in 1934 the reinforcement of the masonry at the base of the foundation by spraying caused a sudden shift in the south by about 10mm and the drawing of the lower layer of groundwater in the 1970s caused the tower to shift about 12mm. These reactions affirm how the tower is built on weak ground, and any method used to stabilize the tower must be sophisticated and complex.

Stable tower

Arranging drilling equipment to absorb soil below the northern edge of the foot of the tower. In 1990, after the bell tower in Pavia fell, although not tilted, a committee chaired by Professor Michele Jamiokowski was founded by the Italian Prime Minister to consult and implement the stability of the Pisa Tower. Many internationally recognized conferences discussing this priceless historical memorial require the preservation of the basic point of the tower with its skillful history and craftsmanship. Therefore any indiscriminate interference with the tower must be at a minimum and the fixed or visible stabilization plan is unacceptable, and in any case there is a risk of increased spillage. collapse of this very fragile masonry block.

The solution was found to reduce the tilt of the tower to a small extent not visible to the naked eye, but to reduce the stress in the masonry and stabilize the foot base. After many years of extensive research, analysis and testing, it is accepted that the method of suctioning the soil, including the installation of many soil straws located next to the foot of the foundation and just below the northern edge of the foot. A number of drill pipes are in the right position to handle the suction process. Starting in February 1999, in a very stressful atmosphere, following a very slow step by step process, carefully monitored, each volume Not much soil is removed from Class A with a special drill. Due to the porous soil, the pores formed because each time the suction is slowly closed, the result is that the surface subsidence is not much and turn the tower a little north.

The work of land suction takes place for 2.5 years; The tilt of the tower is reduced by half degrees. If the tower starts to tilt southward, it may repeat the process of absorbing the soil at some stage in the future. In addition to the suction of the soil, it is also necessary to reinforce some masonry blocks in the most vulnerable points on the south side.

This mysterious tower, this beauty has been stabilized by the method of respecting and preserving both characteristics and attractive interaction with the soil layer.

Leaning tower from the North, there are still cables temporarily attached in the sand suction area.
These cables are safety belts to keep the tower from falling if there is any mistake in handling.