Today, damage to the monument that is a cause of concern
is the splintering of the limestone used
which is resulting in a progressive decrease in the amount of matter in the outer pillars.
We may ask ourselves to what extent it is necessary to replace some of the damaged blocks.
People with various skills were brought together to come up with the best solutions.
Archeologists, architects, engineers, scientists, stone cutters,
and surveyors were invited to participate in the reflections, so that their mastery of today's tools
could serve to save the amphitheater.
For instance, the very latest 3D laser
scanner digital technologies were used to establish a precise
record of the current state of the structure.
The comparison of the ideal digital model,
created in respect of the rules of the art of the Roman builders,
revealed the amount of damage there is.
The degradation occurring at the surface of the stone
is probably due to the combined action of several factors.
The first factor is linked to the technique
of installing large blocks on top of each other
with no mortar.
Other factors may be linked to the progressive deterioration of the building.
For example, the remarkable rainwater drainage system,
built by the Romans, no longer functions as in the past.
As a result, water tends to seep into the structure where is stagnates.
When Barutel limestone, which is found in the pillars of the facade, absorbs water
it expands and loses a significant amount of its mechanical resistance.
Before arriving at the level of the base blocks, we must first quantify the forces
that transit through the structure by calculating the load capacity.
We focused on 5 of the 60 sections, which already represents a model of 5,000 blocks.
The discreet element method we used,
computes the movement of each block while taking account of the external loads
and the contact forces exerted with the neighboring blocks.
By calculating the load capacity,
the forces exerted on each block can be evaluated more precisely.
We can then focus on the most severely damaged blocks
and study more precisely what exactly occurred in the material.
By using a finite element method
we were able to study the roles of the various factors already mentioned.
Here, we are viewing the impact of an irregular contact surface
qdue to the imprecision in cutting the stone.
Now we are taking account of the expansion of the stone when water is present
and seeps into its two very exposed faces.
The blue tone expresses tension in the humid outer layers,
which exceeds the limit the material can support. In reality, this situation would lead to the appearance of cracks.
These cracks get bigger, which causes the splintering of the stone we have observed.
These factors of degradation were probably already known by the Roman builders,
because many elements in the design of the monument seem to have been imagined to avoid them.
However, their effects on the durability of the Arena,
after 2000 years of history, can be better understood
thanks to this multidisciplinary project. The tools developed provide decision making aid,
which offers constructive input in the thorny debate about
the restoration of a historic monument.