The Leaning Tower of Pisa
Group 10
La Torre di Pisa
• The Tower of Pisa is
the bell tower of the
Cathedral
• Construction began
in August 1173
• Work completed by
1360
• Total number of bells:
7, tuned to musical
scale
Technical Details
• The bell tower rises to a height of 53.3 m
above ground level
• Comprises of eight levels
• Weight estimated at 14,500 tonnes
• Outer diameter of base: 15.484 m
• Inner diameter of base: 7.368 m
• Angle of Slant: 13 degrees
• The tower has 294 steps
Galileo and the Tower
Galileo Galilei is said to have dropped two cannon balls
of different masses from the tower to demonstrate that
their descending speed was independent of their mass.
Galileo showed that Aristotle was
wrong, but could not explain why,
so the University of Pisa decided
not to renew his contract.
Other Historical Stuff
• Benito Mussolini ordered that the tower be returned to a
vertical position. Concrete was poured into the
foundation which resulted in the tower actually sinking
further into the soil
• During World War II, the Allies discovered that the Nazis
were using it as an observation post. A decision not to
call in an artillery strike saved the tower
• In 1987, the tower was declared as part of the UNESCO
World Heritage Site along with it’s neighbouring buildings
• Evil Superman apparently straightened the Tower in the
movie Superman III
What Went Wrong?
• Originally conceived as a
straight building.
• Began leaning to the
southeast soon after the
onset of construction in
1173.
• This was caused by the
particular morphological
characteristics of the
ground underneath,
composed of various strata
formed of deposits and
clayish material,
interlayered, at about a
metre of depth, by strata of
subterranean waters.
• Poorly laid foundation and
loose substrate allowed the
foundation to shift.
Attempts At Straightening
• 1838 - Decided to remove the blanket
of earth from the base of the Tower
which had been covered for centuries
• Tower loses equilibrium
• Increased inclination by about 20
centimetres
• 1934 – Mussolini orders 200 tonnes of
concrete be poured into the foundation.
• Inclination increases by a tenth of a
degree, 10mm at the top of the tower
Attempts At Straightening
• 1970’s - groundwater extraction from
the lower sands increased the
movement by about 12 mm.
• These responses showed how very
sensitively poised the tower was.
• 1989 - Commission established to
make recommendations regarding the
safety of the tower and to implement
stabilisation measures
Attempts At Straightening
• 1993 - 600 tonnes of lead weights
applied to the north side of the
foundation via a post-tensioned,
removable concrete ring cast around
the base of the tower.
• This caused a reduction in inclination
by about one minute of arc. Of greater
importance, it reduced the overturning
moment by about 10 percent
• 1995 - The load was increased to 900
tonnes to control the movements of the
tower during an unsuccessful attempt to
replace the unsightly lead weights with
temporary ground anchors
How The Tower Was Straightened
The final solution to correcting the
lean was to remove 38 cubic
metres of soil from underneath the
raised end.
40 drills were used to excavate
the soft estuary silt.
An artificial subsidence was then
created as the drills were withdrawn
one metre and the tower moved
towards the vertical.
The Tower was steadied by steel
cables attached to the first tier
and anchored to the ground.
The Tower Today
• The Tower stands stable
• The inclination remains but
solely as a tourist attraction
• The tower is one of the Seven
Wonders of the Modern World
• The tower has now been
returned to the angle of
inclination it exhibited in the
1830s
Lessons Learned
Ground Investigations
prior to construction
would have saved a
lot of time and effort