The Leaning Tower of Pisa is located in the Italian town of Pisa is one of the most visited European cities. The building of the Leaning Tower of Pisa, and especially its completion, represents the last element in the complement of the ceremonial complex of monuments that enrich the Piazza Dei Miracoli (Square of miracles). 

Case study of Leaning tower of Pisa

• Name: Tower of Pisa, Leaning Tower of Pisa, Bell Tower of Pisa 
• Architect: Diotisalvi, Guglielmo
• Architecture style: Romanesque architecture
• Italian Name: Torre Pendente di Pisa 
• Construction Year: started in 1173, finished in 1399
• Original Height: 60 m 
• Actual Height: 56.67m =highest side; 55,86m =lowest side 
• Stairs: 251 steps 
• Weight: 14,500 tons

Arguments on the tilt of the tower

To the most frequently asked question of how did the tower of Pisa start leaning? Well, the tower tilt began during construction. It is due to an inadequate foundation on the ground. It was too soft on one side to properly support the structure’s weight. The tower began to sink after construction had progressed to the second floor in 1178. The tilt increases in the decades before the structure completes. They have stopped the leaning of the tower by pumping liquid concrete under the leaning side of the tower and it is now safe for the users to walk. 

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Architectural Characteristics of the Leaning tower of Pisa

• Ring shapes diameter – 19.6m 
• Thickness of wall – 4.1m and 2.7m for all other levels 
• Inclination – 5 and half degree to the south 
• 32,240 blocks(ashlars) for facing the exterior and interior of the cylindrical wall structure 
• 15 half columns at the base 
• 180 columns for the base 
• 7 columns for belfry 
• The tower has 296 steps 
• It has total number of 7 bells tuned to musical scale, clockwise 

Construction of  the tower

The tower was constructed as a hollow cylinder. The walls of the tower are clad with marble and the cavity between the outer and inner wall is filled with a rubble and mortar mix. After 5 years the construction paused due to a lack of funds. Then construction resumed in 1272 completing the construction of 12 floors. In 1360, the work began on the bell chamber of the Pisa tower. It required the building of six steps on the south side of the tower, compared to four steps on the north side between the seventh cornice and the flooring of the bell chamber. It took almost 200 years to construct the tower.

The Bells of the Leaning Tower of Pisa 

• The first bell – LAssunta: it was cast in 1654 by Giovaani Pietro Orlandi, weighing 3620 kg 
• The second bell – II Crocifisso: cast in 1572 by Vincenzo Possenti, weighing 2462 kg 
• The third bell – San Ranieri: cast during 1719 – 1721 by Giovanni Andrea Moreni, weighing 1448 kg 
• The fourth bell – La Terza: cast in 1473 and weighing 300 kg 
• The fifth bell – La Pasquereccia: cast in 1262 by Lotteringo, weighing 10144 kg 
• The sixth bell – II Vesprucio: cast in 14^th century and again in 1501 by Nicola di Jacopo, weighing 1000 kg 
• The seventh bell – Dal Pozzo: cast in 1606 and again in 2004, weighing 652 kg 

The 5^th bell that is named Pasquereccia comes fromEaster because it is used to ring on Easter day. The bell is older than the bell chamber itself. It comes from the tower Vergata in Palazzo Pretorio where it is called La Giustizia. The bell was tolled to announce executions of criminals and traitors. This also included Count Ugolino in 1289. A new bell was installed in the bell tower at the end of the 18^th century to replace the broken Pasquereccia. 

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An Alternative Approach 

In 1838, Architect Alessandro Della Gerardesca constructed a walkway around the tower base. Water filled the walkway area after the excavation extended below the water table. The plan increased the tilt of the tower by over one-quarter of a degree. Gherardesco placed a 0.7-meter thick ring of concrete around the walkway to help stabilize the tower, but excavation nearly caused its downfall. In 1934, engineers used grout injection to stabilize the foundation tower. This process led to a displacement of the tower. The tip of the tower tilted 10mm more to the south.  

In 1993, 600mg of lead weights were added to the north side of the tower, attached by a removable concrete ring placed around the base tower. This reduced the leaning by one minute of the arc. Also, it reduced the moment it pulled on the tower by 10%. The load was increased in 1995 to 900mg while engineers attempted to replace lead weights with ground anchors. One unique idea was to drill 10,000 holes in the tower to significantly reduce its weight. The replica is next to the tower leaning in opposite direction to hold the original tower in place. 

Restoration of the Leaning tower of Pisa

A new restoration idea was presented in 1990. It is a soil extraction or soil subsidence. Its goal was to excavate earth from beneath the tower’s foundation on its northern side so that tower would tilt back towards the perpendicular. The idea is to put into motion after various tests on the tower itself and on the soil underneath its foundation. Temporary cables are attached to the 3rd level of the tower. This would support the tower if anything went wrong during the soil extraction. Also, attaching lead weights are to the ends of the cable to ensure that tower remains steady. 

The first soil extraction occurred on February 9, 1999. At first, the tower showed no sign of rotation. Tower had rotated 7 seconds of an arc toward the north by February 23, 1999, but then it rotated back toward the south. Soil extraction had stopped after the tower rotated a total of 80 seconds of an arc by June 1999. Three of the lead weights were removed in 1999 which stopped the rotation. Main soil extraction began in the year 2000 after preliminary extractions had shown vast improvement. Tower has a tendency to rotate to the East throughout the process, so soil also extract is from the foundation’s west side. Tower continued to move northward, and slowly the lead was removed from the structure. The restoration process was finished on June 6, 2001, and the tower had returned to the position it was in before 1838. 

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