tunnel pathology
Despite the fact that the monument suffers deterioration, it is remarkably preserved. Its appearance, nowadays, and condition does not differ significantly from its original one. This can be mostly attributed to its underground nature that kept it protected from both the human and seismic actions. In terms of pathology of the tunnel, two main sources of potential instabilities could be identified. The first source includes potential instabilities at the excavation perimeter and the second includes instabilities associated with overstressing of the lining.
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The tunnel is lined for a length ~230m. The archaic lining of the tunnel is made out of hewn stones. It forms vertical sidewalls and a triangular shaped roof. Its free width is almost 65cm and its maximum height from the walking level up to the apex (crown) of the triangular shaped roof is almost 170cm. It is of a remarkable construction quality and the lining’s hewn stones are so good shaped that practically attach each other leaving no gaps at all. Most impressive are the slightly curved pieces of stone that form the roof. This geometrical type of triangular arches can be found in temples dated back to the 10th century BC. |
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The roman era lining (of a length ~30m) is of similar dimensions with the archaic one, and it is made out of bricks forming vertical sidewalls and a semicircular arch shaped roof. The presence of the this type of lining that was built so many years after the archaic one indicates that roof and sidewall instabilities were recognized, and that if someone wanted to keep the aqueduct in function he had to implement additional protection measures. Both linings were built to protect the tunnel and the water conveying canal in it from rock falls that could damage or block the water pipe and/or make its maintenance an extremely difficult work. |
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At few locations the tunnel lining suffer damages. At the south portal the archaic lining appears significantly deformed; some stones are fractured and slightly removed from their original position. This situation can be attributed to the presence of loose soil at the tunnel portal area and around the tunnel, the shallow cover and the influence of the seismic activity. The tunnel is constructed within scree material that consists of limestone fragments “floating” in a clayey sandy matrix. The ground cover is about 2.5m to 3.0 m thick. This allowed the weathering and the subsequent loosening processes to penetrate down the level of the lining. Remnants of vegetation roots are also visible. The lining becomes more vulnerable to the earthquake forces (that are transferred from the surrounding ground on it) when its confinement (due to the shallow cover) is limited and when the quality of the surrounding ground is poor. In fact the lining’s distortion and deviation from the verticality has a westward direction which is towards the dip of the ground surface. This is also the direction of the highest earth pressure component that acts on it.
At ch 0+184 at the northern tunnel bore, 9 pairs of the roof key-stones suffer significant settlement, distortion and fracture. At that section it is estimated that the tunnel’s roof has been exerted to excessive loads that were transferred to the lining. In the vicinity of this location the geophysical survey has identified a weak rock zone.
Another overstressing at the lining was recognized at the last tunnel part before its north exit. A significant cave-in has loaded the lining’ roof arch and has deformed it. At this point the roof of the lining was not in contact with the original excavation profile. It was built afterwards to protect it from rock falls. The thinly bedded limestone of the area is unfavorably oriented in terms of tunnel stability, having a direction almost parallel to the tunnel axis and a gently eastward dip.
The rest part of the tunnel is practically unlined. Only at very few locations ancient masonry walls support one side of the tunnel excavation only. For almost 800m the ground conditions are visible at the sidewalls and the roof of the tunnel excavation. Potential further deterioration of the rock exists at some points of the tunnel. These are mainly at cave-ins of an unknown age. Such a cave-in exists at ch 531 and it is due the collapse of a portion of loose mylonite in a fault. The collapse has affected the west sidewall and the roof. Potential instabilities are also related with loose rock pockets in the vicinity of significant faults.
At ch 0+184 at the northern tunnel bore, 9 pairs of the roof key-stones suffer significant settlement, distortion and fracture. At that section it is estimated that the tunnel’s roof has been exerted to excessive loads that were transferred to the lining. In the vicinity of this location the geophysical survey has identified a weak rock zone.
Another overstressing at the lining was recognized at the last tunnel part before its north exit. A significant cave-in has loaded the lining’ roof arch and has deformed it. At this point the roof of the lining was not in contact with the original excavation profile. It was built afterwards to protect it from rock falls. The thinly bedded limestone of the area is unfavorably oriented in terms of tunnel stability, having a direction almost parallel to the tunnel axis and a gently eastward dip.
The rest part of the tunnel is practically unlined. Only at very few locations ancient masonry walls support one side of the tunnel excavation only. For almost 800m the ground conditions are visible at the sidewalls and the roof of the tunnel excavation. Potential further deterioration of the rock exists at some points of the tunnel. These are mainly at cave-ins of an unknown age. Such a cave-in exists at ch 531 and it is due the collapse of a portion of loose mylonite in a fault. The collapse has affected the west sidewall and the roof. Potential instabilities are also related with loose rock pockets in the vicinity of significant faults.
