Construction failure of Structure due to Geological drawbacks

--- Leaning Tower of PISA

Overview• Introduction• History of Construction• Characteristics of tower• Initial mistakes• Cause to the lean of tower• History of inclination• Stress due to lean• Efforts to save the tower• conclusion

Introduction

• Located in PISA, Italy at the 'Piazza dei Miracoli' square.

• Bell tower for the Cathedral.• Renowned all over the world for

its peculiar inclination.• Popular tourist hotspot. Building

was shut down to tourists in 1990, but has open up because of extensive restoration efforts by government agencies.

• Building reopened in April, 2001.

History of construction• The construction of the Tower began in 1173 and due to two long

breaks it went on for 176 years. These breaks were most likely caused by war.

• The first break came in 1178, and by that time construction work had only reached the 4th order of the final Tower.

• The second break was in 1278 after having reached the 7th order of the finished Tower. Completion with the rise of the bell Tower was first achieved in 1360 and although completion would have taken almost of the time had it not been for the two shutdowns, these have actually proven to have been crucial for the Tower existence .

Characteristics of tower

• Weight = 14,700 metric tones• Ring shaped diameter = 19.6 m• Thickness of wall =4.1 m, and 2.7 m for all other

levels.• Inclination = 5 ½ degree’s 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 base.• 12 columns for belfry.

Initial mistakes

• Location of tower – ground comprised of layers of sand & clay.

• Layers ran parallel except under the foundation of the tower, where it formed a bow shape.

• The unstable mixture of soil material caused the soil to compact at a different rate, causing the tower to sink 30-40 cm.

Causes to the lean of tower• The unstable mixture of soil – caused the tower to sink to

the south side.• Soil at south side compressed faster than the north side –

weight of the tower was the main factor of tilt.• Tilting was also due to the fluctuations of the water

levels. • This caused the tower to keep shifting, as well as

rotate…later discovered by scientists that the tower’s position shifted in relation to the ground water level.

History of inclination

Stress due to lean

• It was thought that the tower would tip over due to the angle of tilt.

• However, it would Collapse due to enormous stress.• Stones on first few floors had most stress – they had to support

the weight = 14,700 tones.• Stones on south side had stress because of incline.• The stress kept increasing as the inclination increased, therefore

there was danger of the tower collapsing.• The outside of the tower is made of strong marble, but the inside

is made up of rubble, hence the walls cannot support the resulting stress.

Efforts to save the tower - stabilization efforts

First attempt

• The first modern attempt at stabilization of the tower occurred in 1935, when engineers attempted to seal the base of the tower by drilling a network of holes into the foundation and then filling them with a cement grout mixture. 

• However, this only worsened the problem by slightly increasing the lean.  The failed stabilization did result in more cautious approaches by future preservation teams.

Contd.• In 1990, the tower was closed to

the public and apartments and houses in the path of the tower were vacated for safety.  This was partially spurred by the abrupt collapse of another Italian tower (Civic Tower of Pavia) due to masonry degradation.  City officials were concerned that if the Tower of Pavia could collapse simply due to masonry degradation, then collapse of the Tower of Pisa, with its more than 5° tilt, must have been eminent.

Contd.• The preservation team finally

took action in 1992 when the first story was braced with steel tendons, to relieve the strain on the vulnerable masonry; and in 1993 when 600 tons of lead ingots were stacked around the base of the north side of the tower to counterweight the lean. 

Contd.• In response, in 1995, the

team opted for 10 underground steel anchors, to invisibly yank the tower northwards.  However, this only served to bring the tower closer to collapse than ever before. 

• The anchors were to be installed, 40 meters deep, from tensioned cables connected to the tower’s base. 

Contd.• In view of Pisa’s high water-table, the team froze the

underlying ground with liquid nitrogen before any anchors were installed, to protect their excavations from flooding.

• However, it was not taken into account that water expands when it freezes.  The groundwater pushed up beneath the tower and, once the freezing had ceased, created gaps for further settlement of the tower. 

• On the night of September 7, 1995, the tower lurched southwards by more than it had done in the entire previous year. 

• The team was summoned for an emergency meeting and the anchor plan was immediately abandoned.

Soil extraction• Contractors removed soil from the north side

with drilling equipment.• The tower started to sink on the north side,

therefore reducing some of the stress that was building up on the south side.

• Suspension cables were loosely fitted to the tower so it could pull back the tower incase it started leaning..

Soil removing technique

Contd.• Work began in 1999 and halted in

2001 after approximately 77 tons of soil had been removed and the tower had been straightened by 44 centimeters, returning to its 1838 inclination. 

• While more soil could have been removed, the soil extraction program reduced the stress on the vulnerable first story enough to be safe, yet also maintained the distinctive lean of the landmark.

LEANING TOWER OF PISA-TECHNICAL INFORMATION

• Height of 55.86 m (183.27 ft) on the low (south) side and 56.7 m (186.02 ft) on the high (north) side. 

• The weight of the tower is estimated to be 16,000 tons.

• The tower currently leans at an angle of 3.97°, but leaned at an angle of 5.5° prior to the stabilization efforts in the late 20th to early 21st centuries.

Conclusion • The construction failure is only due to

the unsettlement of soil underneath the structure.

• The amount of water content in the soil is more.

• Soil extraction helps the structure to stabilize for a long time without any tilt.

• A minimum amount tilt is provided to attract the tourist.

Thank u.. for the people who done research on this and made history liveable