The Leaning Tower of Pisa By Group 10 Joe Reynolds Emmet Friel Trevor McGowan Claire Cassidy

“La Torre di Pisa” Original Design Bell Tower of the Cathedral of Pisa. 8 stories high 55 metres Weighing 14,000 tons Intricately carved white marble facade

The Tower Begins to Lean Inclination occurred gradually….. On August 9, 1173, architect Bonanno Pisano began construction of the bell tower. When builders finished the first third, they found the structure had tipped 0.2 degrees to the northwest. Consequently construction ceased for a century. By this time the tilt had increased to 0.7 degrees. For another century the Tower sank and tilted to the north, to the east, and finally to the south. On completion, over 200 years later in 1350, the tower leaned 2 degrees to the south.

Reasons for the Failure The Tower was built on marshland of white metamorphosed limestone which was formerly a river estuary. Due to insufficient geotechnical research and consideration, the engineers failed to appreciate the unstable quality of the silty alluvial soil. An unsuitable foundation scheme was chosen. Weak interlayered strata were found at about a metre depth and the foundations of the tower tipped in the soft soil.

Attempted Solutions 1838 – Blanket of earth covering the base of the Tower was removed. BUT This led to the tower losing its equilibrium and increased the inclination by 20 cm.

tonnes of cement injected into the base Deck Level. BUT This actually added a tenth of a degree to the tilt tons of lead ingots injected into the north side to counteract the southward tilt. BUT The tower jumped 1.6 mm to the south.Within 24 hours, engineers began adding an additional 230 tons of lead, and the movement stopped.

The Final Solution In the past century, the most simplest and intuitive solution was developed: Earth was gradually excavated at the side away from the tilt 40 drills were used to remove 38 cubic meters of earth, scooping out the soft estuary silt. The drills were then drawn back a metre to allow the cavity to refill causing an artificial subsidence that edged the tower towards the vertical. The Tower was steadied by steel cables attached to the first tier and anchored to the ground.

The commission recruited by the Italian government in 1990 cost the Italian taxpayer 45 million pounds sterling to prevent the Tuscany tower from collapsing.

A Successful Failure The Tower stands straight today. The Leaning Tower of Pisa was one of the most successful failures of all time….. It is considered one of the seven modern Wonders of the World and the Tower is a major tourist attraction and landmark.