Aug21

Bracing Mdina’s Falling Ramparts

On Wednesday, 18 August 2010, the Maltese Minister for Resources and Rural Affairs (MRRA), Arch. George Pullicino, visited the site of the on-going restoration works around the fortifications of Mdina, the ancient capital of the island of Malta.

Addressing the media, Minister Pullicino stated that the structural instability of the lateral walls and ramparts of Mdina has long been one of the primary concerns facing the conservation of this old fortified city but it is only now that the opportunity to intervene has been made possible with the assistance of European funds.

Mdina’s long history as Malta’s ancient capital, coupled with its strategic and scenic location on a hill in the centre of the island and its rich diversity of architectural heritage features – its houses, palaces, churches and cathedral – not only make it the oldest fortified settlement on the island but, also, one of the most aesthetically pleasing and sculpturally powerful sites to be experienced in Malta. Together with Valletta, Mdina has been one of the main pillars of Malta’s tourism industry. It is surely one cultural and architectural treasure house that the Maltese people simply cannot afford to lose.

Military Architecture.com also believes that from a purely military architecture point of view, the fortifications of Mdina provide a rare and rich combination of unique features that are largely not encountered elsewhere in the Maltese islands ˗ important elements such as the sole surviving remains of Punic, Roman, Byzantine, and Arab ramparts, medieval walls and towers and first-generation Hospitaller bastioned defences.

Amongst these, undeniably is D’Homedes Bastion (or St Paul’s Bastion as it is also known), which represents the only authentic example of a pre-Great Siege period, first generation Hospitaller gunpowder bastion still to be found in an unadulterated state. This bastion was actually the second major Hospitaller bulwark to be erected on the island and contains a unique internal countermine tunnel with a network of explosive flues and shafts designed to the conventions of the Italian system. Its construction is attributed to Antonio Ferramolino, an Italian military engineer to the Viceroy of Sicily, who was  loaned to the knights of St John for a brief period in 1541. The bastion is known to have been under construction in 1547 and was completed in 1551 as attested by the marble escutcheon with the coat of arms of Grand Master D’Homedes placed on the tableau of the parapet of the right face of the bastion (facing saqajja).  The only alterations to the bastion were made to the embrasures in the parapet during the eighteenth century.

D’Homedes Bastion

G.M. D’Homedes’ coat of arms, dated 1551

Actually, the first Italian-style, arrow-head bastion built by the knights, was that erected at Fort St Angelo. Likewise called D’Homedes Bastion, this earlier structure, however, was heavily altered, both internally and externally, in the eighteenth century to allow it to house two gunpowder stores, thereby robbing it of important architectural evidence of the rare typology of early Hospitaller bastions. Therefore, this makes the Mdina Bastion all the more unique and important as the sole example of early Hospitaller military architecture built to the conventions of the trace italienne and containing an in-built countermining device. Unfortunately however, large fissures now cut clean right through the heart of the bastion and threaten to bring down the left half and face of the bulwark. The cause of the problem is a result of the simple fact that the Knights, conditioned by the nature of the terrain, were compelled to project their bastion beyond the edge of the existing rocky outcrop that supported the medieval castle which they sought to reinforce. Consequently, the new bastion had to be partly erected on the clayish foundations.

The problem however, is not limited to D’Homedes Bastion alone, but plagues large tracts of the fortified enceinte, especially where the Hospitaller knights were compelled to project their defensive works beyond the medieval enceinte.

Fissure in the left flank of D’Homedes Bastion

Structural instability

The primary reason for these serious inherent problems revolves around the geological nature of the Mdina plateau. The clayish nature of the site and the peeling effect of the hidden cliff-face, on which rest most of the old lateral walls of the fortress, both make a very large part of the walled perimeter unstable. The ramparts and the structures resting upon the cliff-face are all being subjected to hidden pressures from the shifting ground. This situation is particularly worrying in the areas around D’Homedes Bastion, the adjoining Vilhena Palace, at Despuig Bastion (beneath the Cathedral), and all along Magazines Curtain (see photos).

Online monitoring of problem areas (Courtesy of the Restoration Unit, MRRA)

Undeniably, the active instability of the lateral walls constitutes a major concern facing the conservation of Mdina’s architectural fabric. Understanding that this situation could no longer be ignored without courting great risk to the preservation of the island’s unique and priceless patrimony, the Maltese authorities had set out, in 2004, to design and implement an ambitious project aimed at the consolidation and restoration of the site. The works currently in progress, co-funded by the European Union through the European Regional Development Fund (ERDF), are the result of a long series of studies designed to find the best cost-effective technical solutions to the problems.

These preparations involved a long series of geotechnical and structural monitoring sessions, geophysical investigations (including horizontal geo-radar, seismic tests, and geo-electrical tests), and laboratory tests on soil samples. The effort was further complemented by a topographic and photogrammetric survey carried out by the Restoration Unit. Data relating to the rate of increase of the structural cracks present in the rampart walls and those of the overlying palace rooms were also automatically recorded on a daily basis by means of computerized data- loggers.

Frightening fissures in the vaulted casemates of Magazine Curtain ... inches away from total collapse.

Fissures and subsidence in Despuig Bastion

All the tests confirmed the existence of active ground movement and that the primary mode of failure was observed to be rigid body rotation about the foot of the ramparts’ foundations, with toppling at the top due to yielding of the underlying clay strata.

The results obtained from these investigations were then used as the basis of a design proposal which basically involves the pinning of the ground below the ramparts with various rows of concrete and steel piles inserted to a deep level into the ground. Fundamentally these interventions are designed to arrest the rotation and movement of the bastion walls by:

  1. limiting the plasticization of the clay owing to excessive bearing pressures;
  2. confining the clay under the structures;
  3. binding the fractured upper coralline limestone; and
  4. reducing both the erosion of the substrata and ground settlement.

Two diagrams showing the basic model of concrete and steel piles designed to pin the unstable ramparts below Vilhena Palace (Courtesy of the Restoration Unit, MRRA).

 

Pinning and piling works in progress on the platform of D’Homedes Bastion.

Programme of interventions.

The present ongoing restoration interventions headed by the Restoration Unit within the Project Design and Implementation Division (PDID) of the Ministry for Resources and Rural Affairs are designed to be implemented in three distinct phases. The first phase, of which works are in progress, includes the Vilhena Palace area ( i.e., D’Homedes Bastion, the ramparts underlying Council Square, and  Vilhena Palace), while Phases 2 and 3 involve Despuig Bastion and Magazine Curtain respectively. The works are scheduled to be completed by 2013.

Below: 3D graphic animation showing the type of pinning with concrete piles and steel micro-piles being employed in the consolidation intervention at Mdina – basically aimed at re-stitching the rampart back together!

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MilitaryArchitecture.com (C) 2010

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