1. Salam
2. Perkenalan (name and NIM (3 digits))
In this video, we are going to learn about how the leaning tower of Pisa was saved.
But before that, do you know what is Civil Engineering? How many different types of civil
engineers? And what is creations of Civil Engineers?
Civil Engineering is one of the most ancient types of engineering, focused on structures and
buildings of all kinds.
There are many different types of civil engineers:
1. Municipal (do you want to make a civilized place to live, work and play around the world?)
2. Water resources (do you want everyone to have access to clean water?)
3. Construction (do you want to turn designs of other engineers into reality?)
4. Transportation (do you want to ensure others are safe on their commute to work?)
5. Structural (do you want to design and build the structures that support industries around
the world?)
6. Environmental (do you want to find solutions to the environmental problems?)
7. Geotechnical (do you want to solve design problems related to earth materials?)
8. Surveying (do you want to provide a fundamental for good land governance around the
world?)
So many creations of Civil Engineers. For examples, the building you were born in, the one where
you study, every road you've ever traveled, and every bridge you've ever crossed, etc. One of the
Civil Engineers’ creations is The Leaning Tower of Pisa.
The Leaning Tower of Pisa is perhaps the most famous leaning building in the World. As you
might guess from the name, the Leaning Tower of Pisa is in the city of Pisa. Located between the
rivers Arno and Serchio.
The construction of the tower started in 1173. The Tower started to lean about five years into its
construction when the builders finished the third tier (about 23m high). As the original design
planned a total of eight tiers, so the construction had to be stopped until a solution to the problem
of sinking foundation was found.
The small town of Pisa sits entirely on alluvial soil composed mainly of sand, clay and shells. The
particular composition of this soil makes it very soft and not suitable to stand heavy loads.
So, the reason why did the tower lean, it was because of the unstable soil over. In other word, the
soil underneath the foundation is not strong enough to carry its weight.
Just like a solid material, soil can actually undergo failure in the mechanical sense. At that point,
it no longer fully supports the structure, which is what happened to the Leaning Tower of Pisa.
The foundations of the tower weren’t deep enough to support it after it reached a certain height.
That meant the stress applied by the tower’s mass was bigger than the soil’s bearing capacity which
ultimately shifted the ground and tilted its foundation.
Bearing capacity is tricky to calculate, but essentially it depends on both the depth and design of
the foundation and the qualities of the soil that you’re building into. Since you usually can’t control
the soil, you need to understand it and build a foundation that accounts for any potential problems.
The main property you’ll be interested in is shear strength. As the foundation applies the load to
the ground, the soil redistributes the forces, creating tension throughout the region around it.
Just as we saw for materials, everything has a certain internal resistance to shear stress. The kinds
of forces that act in opposite directions. There are other kinds of stresses to consider, but shear
stress is the most important because it’s the one most likely to lead to failure. Layers of soil that
push past each other can quickly stop supporting a structure’s foundation. The shear strength is the
measure of the shear stress the soil can tolerate before it reaches failure. The higher the strength,
the more stress the soil can resist before it finally gives way. It’s one of the biggest factors that
determines the bearing capacity.
The key to understanding the strength of a particular piece of ground is that soil isn’t one
homogenous thing. Instead, it’s best to consider soil as a collection of tiny grains of rock and
leftover organic matter from living things. The exact materials differ between soils, but in
geotechnical engineering, the focus is on the size and shape of those grains. That’s where the soil
gets its strength or weakness from. When the soil undergoes shear stress, the friction between
layers of soil helps resist the stress and give it solidity. One of the causes of that friction is that the
grains interlock with one another and resist any change to their arrangement. If things do move,
there’s the added friction of the particles rubbing together. Both of these contribute to the shear
strength. Separate from friction is what’s called cohesion, or the tendency for smaller particles to
stick together, like in modeling clay. In fact, it’s often tiny particles of clay or silt that are
responsible for cohesion in soil, so the more clay it contains, the stronger it will be. The size and
shape of the grains, and the cohesion between them, are just some of the properties geotechnical
engineers use to estimate shear strength.
In 1990, a year after the Pavia tower collapsed, the Italian government set up a team of engineers
to tackle the problem of Pisa’s bearing capacity. After trying different approaches, engineers
finally found a solution. The solution to this problem was then to reinforce the soil under the
foundation and to make room for the Tower to compress some of the soil and straighten back up
towards the North (the Tower leans to South).
They did this in the frame of a project launched in 1990. The project total cost was over 30 million
EUR and it lasted 10 years! The project was led by John Burland, Emeritus Professor and Senior
Research Investigator at the Department of Civil and Environmental Engineering of Imperial
College London.
How did they stop the Tower from falling?
The project went through the following phases:
1. Placing counterweights on the base of the Tower, on the North side, to move its barycenter
lower and back to the North, slowing down its tendency to lean towards the South.
2. Harnessing the monument with gigantic steel cables (the kind of cables you find on a
suspended bridge) to prevent it from collapsing during the works and to "pull it back" once
the soil was prepared for this operation.
3. Digging wells under the foundations of the Tower (60 cubic meters of clay were removed).
4. Draining water from the wells.
5. Reinforcing the foundations with concrete (15-meter concrete pillars were inserted into
the ground).
6. Pulling the steel cables to begin the straightening motion.
These engineering solutions proved to be successful as the stabilization works recovered over
50cm of lean, bringing back the Tower around 4° inclination (like 200 years ago).
The works ended in 2001 and the Tower was proclaimed out of danger of falling. Now it’s thought
that the Tower is safe for the next 200 years and this is all that matters to locals, visitors and to the
UNESCO, which in 1987 enlisted the Square of Miracles in the World Heritage List.