The large complex known as Domus Tiberiana is one of the most important on the Palatine and is made up by a succession of buildings which are badly inter-connected.
Compared with the original configuration (Tiberius), in the period from Domitian to Hadrian (I -II cent. BC) there have been constant changes and expansions until reaching its current appearance (the part towards Via Nova) (figure 1).
The first phase, corresponding to the period of Nero, was characterised by a base comprising a casting of Roman concrete profiled with blocks of travertine. The phase under Domitian modified the Neronian scheme: the facade towards the Forum was reconstructed, completing the new front with a long loggia and transforming the Domus into a sort of offshoot of the great Palazzo which was built on the hilltop. Finally, Hadrian continued interventions: large arches were built which passed over the Clivus Victoriae, taking the front of the Palazzo up to Via Nova, with an architecturally spectacular result.
At a later date, some tabernae were built on this front, probably also with the function of constituting a kind of buttress to contain the thrust of the wall, which was perhaps was originally intended to be internal and not a facade (figure 2).
The foundation ground of the original nucleus consisted of tuff rock, while the foundation layer towards the Roman Forum (Via Nova) consisted of silt-clay sediments from the Velabro, the course of which was diverted during construction of the Cloaca Maxima. The original structures (whose walls have thicknesses between 1.20 and 1.50 m) consisted of four levels (figures 1a and 1b):
1. Via Nova (23 m above sea level)
2. Clivus Victoriae (33 m above sea level, ground floor level)
3. Level 41 m above sea level (first floor)
4. Orti Farnesiani level 51 m above sea level (coverage)
.Most of the structures collapsed in ancient times and the remains were covered with soil, which permitted realisation of the gardens and terraces of the “Orti Farnesiani” on the upper level.
INVESTIGATIONS AND INTERVENTIONS CARRIED OUT IN THE PAST
In 1870, major excavations took place at the Roman Forum, and in 1900 the structures were uncovered: these excavations certainly negatively affected the stability of the structures facing the Forum.
Around 1891, excavations were carried out in the area close to the Via Nova and on this occasion the walls of the orthogonal tabernae on Via Nova were restored.
In 1960, the concrete brick floors covering the second level on the Clivus Victoriae were built, while in 1970 a first system of perpendicular metal tie-rods was put in place Via Nova to interconnect various detached walls.
From 1985 for a period lasting around 10 years, a series of topographic measurements was carried. These measurements indicate that there are not only downward vertical movements (about 0.2-0.4 mm/year) with cyclic behaviour (probably of a seasonal climatic nature) but also a shift towards the Forum in a north-east direction with maximum values of 5 mm (1985-95). At the perimeter of the Domus towards the Forum, the surface layers have been eroded and covered by alluvial silt-clay deposits.
In 2000, the “rigid” tie-rods were replaced by a system of new tie-rods (Diwidag bar type with diameter of 26 mm), anchored with leaf springs so as to have a deformable bond such as to maintain the substantially constant forces, independently of (or in any case little affected by) shifts induced by movements non-stabilised ground, as well as by thermal effects (figures 3-5). A similar technique was applied to support the vaults of Palazzo Ducale in Genoa and for the vaults of the Basilica of St. Francis of Assisi. In this way, it was possible to achieve a contrast against differential movements produced by soil sliding without, however, purporting to block them, thus avoiding dangerous concentrations of stresses. This intervention was associated with a monitoring system able to predict adverse developments and take timely corrective action, such as adjusting the tension in the chains, etc.
Monitoring provided interesting data and, in particular, showed that the chains, as designed, undergo moderate cyclic variations due to thermal effects (of the order of 300 kg/sq. cm.). The relative displacements measured at the ends of the chains, which were slight, show that these do not significantly affect the stress state in the chains due to “flexible” anchorages made with the system of leaf springs (figure 6).
The most important lesions in the vast existing crack pattern, in particular those affecting the separation baffle between the 5th and the 6th spans, result in movement, even if with modest values.
DIAGNOSIS: STATE OF CONSERVATION, INSTABILITY, DEGRADATION
The state of instability that characterises the area in question can be broadly divided into two categories: the first concerns the problems affecting the entire structure as a whole; the second is related to events such as injuries, cracks caused by localised crushing or degradation of materials, etc. Even if on the one hand these local phenomena do not prejudice the global safety margin of the structure, on the other hand they reduce durability and can represent a source of danger for persons.
The signs of instability that are detectable today are difficult to interpret in relation to historical phases of construction, soil dissimilarities, the effects of excavations that have followed one another over time, previous reconstruction and reinforcement interventions, as well as the earthquakes that more than any other event have contributed to collapses and instability (among the strongest earthquakes, we recall those of 434, 801, 847, 1347 and 1703 which caused major damage to the Colosseum.
The structures which survived collapses, to which degradation and neglect also contributed, are affected by diffuse lesions, detachments, misalignments and material degradation.
The front of the Forum is today completely detached from the body behind. Lesions affect all the transverse walls up to the terrace at the level of the Orti Farnesiani.
Vertical lesions cross the two paved levels of the Domus up to the level of the Orti.
The foundations of the northern part towards the Forum, as noted above, are subject to worse behaviour than those behind; the presence of silt-clay layers which affect the eastfacing zones more broadly than the west-facing zones, although of discrete mechanical characteristics, may have contributed to the instability that is detectable today, even though all the evidence suggests that earthquakes certainly played an essential role in collapses.
Evaluation of the instability and forms of degradation that have affected the Domus is briefly described in the following paragraphs.
Spine walls between Clivus Victoriae and Via Nova
The entire area is characterised by a marked crack pattern of complex interpretation, which has also been the subject of monitoring for some periods (figures 7-8).
This crack pattern was already evident from the times of the excavations and demolitions in the 19th century, at which time some 16th century structures of the Farnese were removed, in part also close to the structures in question, along the Via Nova.
There are deep lesions of isolated or branched detachment on the orthogonal dividing spine walls at Clivus Victoriae, which show a tendency to detachment between the fronts downstream and upstream of the area in question, which are visible both internally and externally. Such lesions are evident on the bases in Roman concrete of some buttressses on the front along the Via Nova: in some areas the width is greater at the bottom and tends to narrow further up.
Vaults of areas between Clivus Victoriae and Via Nova
Even the vaults in concretion on the first level are affected by instability: most of these are visibly damaged by the fractures affecting the vertical walls (figure 9).
Front on Via Nova and Tabernae
The same front displays localised sections of heavily damaged and disaggregated Roman concrete such as to require the necessary provisional props of pipes and joints (figure 10). The party wall between the structures of the Clivus Victoriae and the tabernae on Via Nova is detached from the structures behind it, and also presents significant lack of material in the thickness (figure 11).
The front of the tabernae on Via Nova consists of three levels of walls parallel to the Via Nova which are disconnected between them. These walls are affected by structural instability, to which continuous infiltration of rainwater has contributed.
Along the east-facing paved corridor (Clivus Victoriae), a major lesion can be seen at the base, which was a the lready visible during the excavation of the ‘70s; lately it has been brought to light, confirming the disconnection and a related movement of the entire front overlooking the Via Nova. Some pillars along the Clivus Victoriae show evident signs of crushing accented by detachment of the curtain from the original core through vertical lesions (figure 12). Since the loads are small in relation to the resistant section, the cause is probably to be sought in the earthquakes or overload corresponding to differential sinking.
On the other hand, some pillars on Clivus Victoriae present failures at the springer of the arches (figure 13). The stretch of the east-facing vault is affected by a large crack pattern and is detached from the south wall.
The corner area between the Via Nova and Via S. Teodoro has wide diagonal lesions that are probably due to the effect of earthquakes as well as settling of the soil that have occurred in the area (figure 14 and 15).
Structures upstream of Clivus Victoriae
The structures upstream of Clivus Victoriae are affected by a conspicuous crack pattern that seems to confirm the tendency to disconnection of the entire north-west towards the Via Nova and the Forum: in fact, some lesions affect the orthogonal dividing walls at Clivus Victoriae and are mostly feedthroughs with a vertical progression, while others affect arches, vaults and lintels running parallel to the clivus (figure 16).
The interventions can be divided into global concerning the behaviour of the ensemble and local concerning individual elements. The global interventions essentially concern instability of the facade, and since it is currently neither necessary nor convenient to intervene on the foundations, the project is oriented towards recreating a structural continuity and containment of pressures, in addition to earthquakes. The system of shackling already in place creates a quite effective anchorage in the various walls parallel to the facade although it must be extended to structures upstream of Clivus Victoriae (figure 17). The chaining must be supplemented by interventions to create a structural solidity between the various juxtaposed walls (by means of injections, insertion of connecting tie-rods, etc.).
Local interventions essentially concern rebuilding of the vaults in order to raise the paved level and rearrange the terrace on the Orti Farnesiani, in addition to eliminating the old concrete brick floors. The coverage vaults on the second level towards Clivus Victoriae should be reconstructed in accordance with the ancient instructive techniques. Another intervention concerns the construction of some tabernae which also have the function of stiffening buttresses.
The first operation under way concerns the compensation of lesions in the spine walls and vaults, integrating them in correspondence with the failures (figure 18). However, the core problem of the current project concerns seismic protection for a building that is intrinsically vulnerable due to the different quotas of strength of the foundations and the unevenness of the land involved. Seismic improvement is based on reconstitution of the walll “box” by compensating for the lesions, giving the walls a tensile strength by means of the insertion of some enchainments. The mounting system has shown a substantial stability of the phenomena for which it was planned to replace the existing chains, anchored to the flexible leaf springs with new enchainments partly inserted inside the masonry, and therefore not visible. Parallel enchainments have also been inserted to the front of the Via Nova with a view to creating a behaviour of the whole, eliminating local phenomena of tilting of the front of the header, not opposed by the vault that originally was to cover the environment concerned by the ramp. Reorganisation of the “heart” of the Tiberian Complex also includes reconstruction of the vaults and orientation of the terraces that cover the Domus complex. The new vaulted structures are in pieces of tuff mixed with mortar made of natural hydraulic lime of different thicknesses depending on the light cover.
[by Alessandro Bozzetti]
NOTE 1. The interventions are carried out by the Archaeological Superintendence of Rome under the guidance of Arch. M.G. Filetici.