This document discusses the geotechnical issues related to the Leaning Tower of Pisa. It was built over three phases from 1173 to 1370 on a shallow foundation in soft, compressible soil consisting of layers of clay, sand and gravel. This caused differential settlement and instability issues during construction. Lessons highlighted include the importance of thorough geotechnical investigations, understanding soil properties, using deep foundations for heavy structures, and ongoing structural monitoring and maintenance for long-term stability.

1. THE LEANING TOWER OF PISA
THE GEOTECHNICAL ISSUES AND LESSONS.
GROUP 2

2. GROUP MEMBERS
1. RUHANGAYEBARE HILARY 22/U/21085/PS
2. ONDOGA JOHN BISMARK 21/U/19904/PS
3. AMPUIRE IGNATIUS 22/U/5767
4. MUSIIME SOLOMON 20/U/19688/PS
5. ASIIMWE ANNAH 22/U/5813
6. OJOK OSCAR BRIAN 22/U/21082/PS
7. KYABANDIHO VICTOR 22/U/21070/PS

3. INTRODUCTION
• Known as the Bell Tower of
Piazza del Duomo in Pisa
(Italy) .
• Built during a period of two
centuries from 1173 to1370.
• Built in 3 phases.
• First phase, 4 floors were
built over a period of 5years;
1173-1178.
• Second phase from 1272 to
1278 with the completion of
the 7th floor.
• Third phase with the
construction of the bell tower

4. INTRODUCTION
• The total height of 58.4 m
measured from the
foundation.
• Ring- shaped cross
section, with an external
diameter of 19.6 m at the
base.
• Estimated weight of the
Tower is 14500 tons.
• The current tilt of the
structure is about 5°
towards the South.
• Leading to an offset at the
top of about 5 m

5. The Leaning
• The Tower started leaning to the
north,at the beginning of
construction reaching a
maximum tilt of about 0.5°.
• Gradually switched to the South
to a maximum tilt of about 5.5°
in the early 1990s .
• The last abrupt increase in
inclination of the Tower in 1838
,due to the digging of the
Catino.

6. GEOTECHNICAL
ISSUES
SOIL CONDITIONS
• A 10 m thick layer of sand and
loam below the circular
foundation.
• A clay layer with shell deposits
found up to a depth of 25.
• Followed by a 3m sand and
12m clay layer located at a
depth of 40m

7. GEOTHECHNICAL
ISSUES
SUB SOIL
• The subsoil of the Leaning Tower of Pisa belongs to the
alluvial deposits.
• A geological profile at a depth greater than 60m has been
defined into three horizon.
1.Horizon A: upper variable deposits from 3 to 10m
2.Horizon B: clayey deposits from 10 to 40m
3.Horizon C: lower sand deposits from 40 to 60 m

8. GEOTHECHNICAL
ISSUES
• Horizon A- chaotic nature and
consists of strata of silt, clay and
sand of very limited persistence.
• Horizon B extends to a depth of
40 m and is subdivided into four
distinct sub-layers of soft and
sensitive Pancone clays.
• Horizon C mainly consists of
eolian sands (i.e. coastal dunes)
with interbedded layers of silt and
clay having a micro fauna typical
for salt water and similar to that
in Horizon B.

9. GEOTHECHNICAL ISSUES
• Available data representative of soil parameters
from laboratory tests.
 Stiffness modulus, Es=2-19MN/m²
 Coefficient of permeability, k=10^9-10^11 m/s
 Undrained cohesion, Cu=40-60 kN/m²
The soil could barely carry one half of the present
weight of the tower
(tower weight W= 145 MN, mean foundation stress
δ=480 kN/m²).

10. GEOTHECHNICAL ISSUES
DURING CONSTRUCTION
1 Foundation instability
• The tower being built on a shallow foundation
(3m) on soft, compressible soil, resulted in
differential settlementt.
• Managed by altering the design of the upper
floors to compensate for the lean and prevent the
tower from toppling over
2 Soil composition.
• Complex mixture of clay, sand, and gravel
underneath the tower posed challenges in
predicting soil behaviour and stability.
 Stabilisations
 Extraction of soil from beneath the Tower using
the Corkscrew drills.

11. GEOTHECHNICAL ISSUES
Stabilizations
 Micro piles inserted into the
ground to reinforce the
foundation and provide
additional support.
 Lead counterweights to
counteract the remaining tilt.

12. LESSONS
• Importance of thorough geotechnical investigations.
• Understanding soil properties and behavior is crucial.
• Deep foundations are essential for heavy structures.
• Structural monitoring and maintenance are vital for long-term
stability