IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
09-2013
Immediate Interventions for the Restoration of Patras’ Roman Aqueduct Marilena Mentzini1 1
Structural Engineer, Ph.D., 6th Ephorate of Prehistorical and Classical Antiquities, Ministry of Culture and Sports, 197, Al.Ipsilantou str,, 26110, Patra, Greece (E-mail :
[email protected],
[email protected]) Abstract The present paper presents the process directed to the undertaking of the immediate measures as to the protection and safety of the monument against dynamic actions, as well as stresses and damages which can probably occur due to its deteriorating form and the implementation of the project of the Small Ring Road of Patras in the neighborhood. The immediate interventions are prioritized and include in this first phase: A) Stabilizations, prestressing using wire ropes, injections grouts and joining together parts in the positions of danger cracks and/or of deteriorated sections B) Complements on the missing parts on the base of the piers in the south area C) intervention on the surviving arch and to the preserved part of its respective remaining overlying one, which include supportings, raking shores, prestressing using wire ropes, and injections grouts. In order for these to be achieved, actions precede or run at the same time, which are related to the preparation and the layout of the area for the application and protection of the interventions, such as exploratory research work, rainwater management etc. Keywords: monument; arcade; opus testaceum; water; drainage
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
INTRODUCTION The Roman aqueduct of Patras, a huge technical project, which proves the major development of engineering at the period, still stands as a commemorating testimony of the past in several areas of the city. The access to its best preserved part which dominates the Aroe valley remained up to recently difficult. The future opening of the Small Ring Road in this neighborhood provides the potential of immediate sight and promotion of the monument, which nevertheless presents intensive structural problems. The archaeological site of the Roman aqueduct is under the supervision of the 6th Ephorate of Prehistorical and Classical Antiquities, which went on to the compilation of a research study with the title “Protection & Restoration of the Patras’ Roman Aqueduct on the Aroe’s valley – A΄ phase: measures of immediate strengthening” (Mentzini and Toumbakari 2011). The application of the study which was unanimously approved by Central Archeological Committee, was incorporated in the Regional Operational Programme “Western GreecePeloponnesus-Ionian Islands” with a budget of 225.000 €.
HISTORICAL APPROACH AND CONSTRUCTION TECHNIQUE After the proclamation of Patras into Roman Colony in 14 BC (Colonia Augusta Achaia Patrensis), the city developed into a large civic centre and its needs in water supply increase. Thus, an excellent technical work is constructed, 6.5 km long, starting from the Diakoniaris spring in the Area of Romanos. It crosses the slopes of the hills through vaulted conduits, while the dingles are bridged with an arcade the top of which is crossed by a large open channel. The best preserved part is located in the valley of Aroe a position also known to the travelers of the 17th and 19th century (Weller, Pouqueville etc.), where 14 pillars are preserved in situ with struts, 110m long and a double, 14 m in height arcade. It was probably constructed in the beginning of the 2nd century AD from Emperor Hadrian. The aqueduct with restorations and additions served the city, at least part of it, until its final abolishment in 1873. The masonry of the Roman aqueduct has a composite structure (opus testaceum) made of two external fired-brick walls (opus latericium) and a concrete core (opus caementicium) -a kind of multi leaf masonry. This innovative technique developed in Roman times is characterized by astonishing rapidity in rising huge buildings, quality of the materials used, and attention reserved to their production and selection. Obviously, the mechanical characteristics of the wall depended almost exclusively on the strength of the opus caementicium (Giavarini and Santarelli 2001, Giavarini et al. 2006).
PATHOLOGY DIAGNOSIS Major Structural Damages Losses, but also local fractions of the fired bricks, that is of the external layer of the bearing structure and restricted problems to the mortar between the bricks. These problems are presented in areas of changing stiffness and discontinuity during the construction (different building phases, joint separation) which can also be affected by the action of plant roots. The loss of mortar is intended due to the natural processes (wind erosion, water infestation due to direct incidence onto the surface-direct wetting, rising damp etc.), chemical ones and
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
biological actions and in process due to the creation of failure deriving from static and dynamic loads. In addition the revealing of the core of the masonry (opus caementicium) creates problems to the ancient concrete, such as cracks and detachments. Intensive loss of masses in critical for the stability of the structure areas -problems on the foundation of piers. The latter, is deriving from changes in temperature, wind, the corrosive action of the rainwater and of the mechanical stresses due to the growing of the roots of the plants. These factors are strengthened from static loads and dynamic actions, since there was a change of the bearer due to the loss of its frame and diaphragmatic function. Vertical cracks to the masonry of the struts, sometimes thru and expanding to almost all of its height, which denote a sliding of its free part. The same existence of the struts in the initial structure (a rare incident in the architecture of the ancient aqueducts) (O’Connor 1993) leads to the conclusion of improper foundation ground of the pillars. The valley of Aroe must have been run through a river with unstable riverbed, no longer existent. Today, the foundation ground of the pillars presented as macroscopically loose and clayed. The combination of its composition along with its place within the surrounding basin creates a locally intense stagnation of the water, which contributes further to the loss of masses as previously referred. Detachment of the only surviving arch from its springing, through a thru crack. It derives from a combination of sliding to the N-S axis as well as from the contact loose due to material loss and degradation, and these factors are intended from the direct wetting due to its position. Horizontal and vertical cracks extended all over the respective remaining overlying part, mainly as a result of the change of its structural function from arch to cantilever.
Photo 1 General view from SE of the Roman aqueduct before intervention. The structural damages are clearly visible.
IMMEDIATE RESCUE MEASURES PROPOSED For the immediate protection of the monument the rescue measures are prioritized as follows: Tackling cracks Strengthening of the core (locally in the cracks) with injection grouts of the proposed composition (Mentzini and Toumbakari 2011), which will occur from the sampling and analysis of the ancient mortar (Toumbakari et al. 2000). The detached parts will be joined together with proposed material. In case the positioning, the preservation and the geometry of the pieces allow, they will be prestressed with iron wires to the main mass of the monument.
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
Geotechnical survey of the surroundings of the monument (which consists of deposits) and consequently construction of a drainage net. In this way the proper background will be developed, so that to confront the danger of the problematic foundation of the piers, to protect the proposed interventions and to avoid of future sliding cf. Major structural damages: vertical cracks on the masonry of the struts, detachment of the only surviving arch. Restoration of the problematic foundation of the piers Local fillings of the lost parts with the in situ construction of a stone retaining wall. The material used will consist of the proposed mortar and cobblestones of similar dimensions to the ancient ones. The sections added will be founded on the already existent base of the piers, which will be revealed after the withdrawal of the deposits and cleared from the damaged areas, in order to create a solid background to build on. The separation between the new and the ancient surface will be performed with the use of fiberglass mesh for reinforcing. Additional measures in the area of the arches The surviving arch will be supported with the construction of a metallic falsework arrangement. This solution was selected because of the advantage of the easy control and access, while its shape allows passage under the arch and aesthetically adapts to the environment by reminding the construction technique of the ancient arch. The raking shore chosen to support the respective remaining overlying part will be of wood. The contact of the supportings, will be accomplish via elastic inserts of neoprene type.
RESEARCH REALIZATION After the approval by Central Archeological Committee, and the incorporation in the Regional Operational Programme “Western Greece-Peloponnesus-Ionian Islands” with a budget of 225.000 €, a work-site was installed around the monument, paths were created and scaffoldings were placed. The works began with the use of two prestressing wire ropes on the horizontal level in the upper part of a pier and one on the horizontal and two on the vertical level on the upper end of the remaining overlying part of the arch, for the containment of the loosened masses. In undisturbed sections penetrations implemented to put anchored bolts, which were fixed with resin and in sequence the wire ropes were fastened on them. In addition, the wooden truss of the raking shore of the remaining overlying part of the arch followed the way described in the study. In this way, the safe continuation of the remaining actions of restoration was accomplished.
Photo 2 Detail of prestressing wire ropes on the upper end of the remaining overlying part of the arch.
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
Photo 3 General view from NE of the Roman aqueduct during the intervention. The wooden raking shore of the remaining overlying part of the arch, is depicted on the left.
Laboratory Tests on Mortars–Injection grouting In the next phase laboratory tests were performed on samples of ancient mortar in order to design counterpart compositions for: the injection grouts, the new mortars between the firebricks, the mortars for sealing gaps in general and the fillings of the lost piers. These laboratory tests included: 1. Gradation of: (i) the coarse aggregates included in the ancient mortar and (ii) the local sand used in the new mortar composition. 2. Qualitative mineralogical assessment of the ancient mortar by means of X-Ray Diffraction method (XRD). 3. Determination of the apparent porosity and the apparent density of the ancient mortar. 4. Thin section pertography of the ancient mortar using an optical microscope apparatus. 5. Determination of the tensile strength of the ancient mortar. 6. Evaluation of the injectability of the compositions suitable for grouting by means of the Marsh funnel test method. 7. Grout stability (segregation resistance) by means of a test method for bleeding of grouts. 100
90
80
70
60
50
40 δείγμα 1 30 δείγμα 2 20 δείγμα 3 10
0 0,01
Ρωμαϊκό κονίαμα
0,1
1
10
Figure 1 Gradation curves of the aggregates comprising the roman mortar and of the sands currently available; a distinct difference is evidenced.
Using this experimental data Dr. E.E Toumbakari designed the compositions of the new mortar and grout.
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
Table 1 Mortar composition Materials White Portland cement Lime Pozzolan Sieved sand (sample 2) (0-mm) Unsieved sand (sample 2) (0-4mm) Superplasticizer
Relative contents 35% 22% 25% 43% 75% 75% 25% 1% of binder
22-24 March 2014
Absolute contents 9% 5% 11% 56% 19%
Grout Composition for wide cracks (%, by weight content) Lime: 10% Natural pozzolan: 18% White Portland cement: 12% Sand (maximum aggregate size < 0.8 mm): 60% Superplasticizer: 1.5% of binder During grouting, both injectability and bleeding tests were conducted on site. The injection nozzles were numbered and the grout intake was recorded for each nozzle. A record of other application details, such as the occurrence and the spatial tracing of grout leakage was also kept. The determination of: (i) the tensile strength of the ancient mortar (by means of direct tension tests) and (ii) the tensile (flexural) and compressive strength of the new mortar and grout at 28 and 90 days was realized at the Structural Materials Lab of the University of Patras Civil Engineering Department. The average tensile strength of the ancient mortar was found to be equal to 0.84 MPa, while the average tensile strength of the new mortar was found to be equal to 3.4 MPa (at 28 days) and 6.1 MPa (at 90 days). For the grout, the respective values were equal to 0.7 MPa and 2.5 MPa. The average compressive strength of the new mortar was equal to 21.9 MPa (at 28 days) and 26.7 MPa (at 90 days); for the grout, the respective values were equal to 3.4 MPa and 5.9 MPa.
Photo 4 The injection grouting process.
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
Supporting of the surviving arch – Reconstruction of the loss part on the foot of the piers The supporting of the surviving arch began after the completion of the injection grouts, the filling with new mortars between firebricks, and gaps in general, and after the grading of the surface of the intrados of the arch. The falsework arrangement constitutes of four similar metallic frames (the upper part has the scheme of a trussed arch forming by double T -beams IPE 160), which are founded through eight columns (HEA 160) on reinforced concrete bases and are connected with beams also of the same kind (the quality of all the metallic elements is S 275). For the construction of the aforementioned bases an excavation was carried out in the area underneath the surviving arch and the extrados of the continuous arched base of the arcade of the Aqueduct. The ancient surface was covered with an elastic insert for its protection from the frames’ foundation. The whole new structure was painted with the appropriate color to match the adjacent ancient section of the fired bricks. After the strengthening of the upper part of the monument, the safety approach to the critical areas on the feet of the piers could be possible, and consequently the following construction of the stone retaining walls under the already given specifications. It is worth to be noted that colorific pigment was added in the mortar so the final result looks similar, but not exactly the same, to the ancient one. In this way, there is no confusion to the perception of the viewer with reference to the distinction between the intervention and the original ancient structure.
Photo 5 Detail of the upper part of the supporting of the surviving arch.
Photo 6 During the construction of the stone retaining walls.
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
Geotechnical sampling, engineering and design The survey of the soil was performed by sampling drilling. It is noted that the immediate area north of the monument is considered as ground level 0.00m in measurements taken. As such, the ground level south has an average height approximately -3.30m. Two sampling drillings implemented on the North in depth ca 12.00m and two on the South in depth ca 7.50m with SPT tests (Standard Penetration Tests) and undisturbed soil’s samples was taken. The sampling was continuous and the percentage of the coredrilling reached up 100%. It is worth mentioning that an aquifer was revealed during the process. The data obtained from each drilling are recorded into protocols, and the corresponding geological sections are plotted. The underground water level change was observed by piezometers.
Photo 7 The implementation of sampling drillings on the south area.
The assessment of the results, as far they concern in situ and laboratory tests, show that the geotechnical situations of the lower area (South) up to the depth of 12m are similar, with a normal increase of the strength depending on the distance from the surface. In the first 0.50m the soil consists mainly from sandy clay, while then and to the end of the sampling drilling dominates clay of brown to grayish to green color, where there had not found a serious amount of sand and gravels. In the higher area (North) there are a great amount of sand and gravels (clay 60%, sand 20%, gravels 20%). As a result, the aquifer found a passage to the lower area where the clays are more cohesive (96 %). The waters find no way out and flow as an artesianism phenomenon of the superimposed aquifers. The given solution includes three drilling on the North of the Arcade and one on the South. The distances between them is appropriate, thus a proper radius of influence to each other exist. In each an underwater pump was placed, and when the water level rises the drain empties through pipes in the neighboring channel of the Small Ring Road (Mammis 2013).
NUMERICAL ANALYSIS OF THE BEARER In the course of a further in detail analysis of the Roman aqueduct’s structure two research studies has been held titled “Static’s failure scenarios of the maintain part of the Patras’ Roman aqueduct” (Mentzini 2012) and “The influence of the foundation on the failure of the maintain part Patras’ Roman aqueduct. Numerical analysis in the initial ancient bearer” (Mentzini 2013). The aim is to determine the critical sections prone to failure under ordinary conditions or under dynamic actions, and consequently the interpretation of the already appeared in situ damages. For these reasons, the structure was explored numerically to find
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
the most severe stress field using the Finite Element Method with the aid of the appropriate software (Sap 2000, 14). The numerical model simulation and the following numerical analysis yield satisfactory results, which confirmed the failures observed.
Figure 2 A part of the meshing numerical model.
CONCLUSIONS The problem of restoring and conserving an ancient monument is an extremely complicated multidisciplinary scientific task, and a series of problems must be taken under consideration and resolved before a final decision is chosen (Mentzini 2006). These problems vary from elementary ones, as for example the strength and deformability of the materials used, to rather complex ones, such as the preservation of the structural system, the determination of the minimum possible intervention, the reversibility of the interventions and of course their durability. Archaeologists, architects and engineers collaborate in order to meet the final target that is the extension of the life of the monument. The decisions made are usually a compromise between various, and often contradictory, aspects. In this paper the steps of the immediate interventions for the restoration of the Patras’ Roman aqueduct are presented to expose all the difficulties, but also to shed light on how in this field the scientific horizons are not restricted in certain specializations, but give the advantage to feel instantly like a homo universalis.
Photo 8 General view from S of the restored Roman aqueduct
IWA Regional Symposium on Water, Wastewater and Environment: Traditions and Culture. Patras, Greece
22-24 March 2014
ACKNOWLEDGMENTS The author would like to thank the persons who participated in the project. The technicians: Yannis Sampanis, Polytimi Tomara, Nektarios Vasiliadis, the civil engineer George Konstantakopoulos, and Dr. Eleni –Eva Toumbakari structural engineer. The help of Lampis Tomaras, technician of the 6th Ephorate of Byzantine Antiquities is acknowledged. Additionally the author would like to express her sincere gratitude to the archaeologist Dr. M.Tsakoumaki, for possessing a clear engineer mentality.
REFERENCES Mentzini, M. and Toumbakari, E.E. 2011. Protection & Restoration of the Patras’ Roman Aqueduct on the Aroe’s valley –A΄ phase: measures of immediate strengthening, The General Directorate of Antiquities and Cultural Heritage Archive, Athens, Greece. Giavarini, C., Santarelli, M.L. 2001. Dimensional variations of Roman Masonry subjected to wetting/drying circles, Conservation and Management of Archaeological Sites IV, 4, 213. Giavarini, C., Samuelli Ferretti, A. and Santarelli, M.L. 2006. Fracture and Failure of natural Building Stones, Mechanical characteristics of Roman “opus caementicium”, Springer, The Nederlands, 107-120. O’Connor, C. 1993. Roman Bridges, Cambridge University Press, Cambridge, Great Britain. Toumbakari E.E., Georgali, B., Papadopoulos, Ch. and Vachliotis, Ch. 2000. Compatible Materials Recommendations for the Preservation of European Cultural Heritage, PACT 59, Characterization of the in situ materials as a condition for the design of repair materials – Application on the mortars of the fortification walls of Kos, G. Biscontin et al eds, Athens, Greece, 191-200. Mammis, N. 2013. Geotechnical research in the neighbourhood of the Patra’s Roman Aqueduct on the Aroe’s Valley, protection and restoration included, The 6th Ephorate of Prehistorical and Classical Antiquities Archive, Patras, Greece. Mentzini, M. 2012. Static’s failure scenarios of the maintain part of the Patras’ Roman Aqueduct, The General Directorate of Antiquities and Cultural Heritage Archive, Athens, Greece. Mentzini, M. 2013. The influence of the foundation on the failure of the maintain part Patras’ Roman Aqueduct. Numerical analysis in the initial ancient bearer, The General Directorate of Antiquities and Cultural Heritage Archive, Athens, Greece. Mentzini, M. 2006. Structural interventions on the Acropolis Monuments, The Acropolis Restoration news 6, YSMA, 15-18.
