Mdina, Malta’s medieval
capital and later Baroque fortress, one of Europe’s finest examples of an
ancient walled city, lies on a geologically sensitive area. In fact, many of
its bastion walls and adjoining buildings, lying on the outer perimeter of the
town, have serious structural problems. The main scope of this project was to
consolidate the fragile terrain on which the bastion walls and historic palaces
such as the Vilhena Palace at the entrance to Malta’s medieval capital city are
built in order to diminish and possibly stop further settlement and damage of
these historic legacies.
In 1966, UNESCO was
commissioned to prepare a technical report on the interventions necessary to
arrest the movements and its conclusions highlighted the importance of
controlling the hydrology of the area and the underpinning of the bastion walls
with bored piles. Later studies proposed underpinning of the bastion walls with
the tip of propped cantilevers supported on micro-piles. A study commissioned
by the Maltese Government in 2002 for a geotechnical investigation of the
bastions perimeter around the Vilhena Palace, after significant movements in
the area were recorded, involved a site monitoring program linked with climatic
observations that was carried out for a period of 18 months. The geotechnical
investigations indicated that there was significant ground movement in certain
areas, particularly in the area of Council Square.
A two dimensional
computer model using a dedicated finite element program was made using the
material and geometric data gathered. The results of the computer model formed
the basis of a design proposal which had the main scope of arresting the
rotation and movement of the bastion walls by:
· Limiting the
plasticization of the clay due to excessive bearing pressures;
· Confine the clay
under the structures;
· Tie together the
fractured upper coralline limestone;
· Reduce the erosion
of substrata composed of orange sand, yellow and blue clay;
· Ground improvement
by geotechnical processes to increase the allowable bearing pressures and to
reduce settlement.
The historic
fortifications of Mdina constitute one of the main pillars of Malta’s built-up
physical heritage assets. As an architectural monument, its fortifications
document both important stages in the Island’s history and also the development
of military architecture throughout the Middle Ages and early modern period.
The city’s fortifications also form an integral and visual part of the island’s
cultural landscape. The larger part of Mdina’s fortifications also play an
important role in tourism.