The Leaning Tower of Pisa
By Group 10
Joe Reynolds 01835521
Emmet Friel 01373480
Trevor McGowan 01446452 Claire Cassidy 01014137
“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.
• 1934 - 200 tonnes of cement injected into the base Deck
Level.
BUT
This actually added a tenth of a degree to the tilt.
• 1995 - 600 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.