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GEOMORPHOLOGICAL HAZARD AFFECTING THE MEDIEVAL CITADEL OFSIGHISOARA (ROMANIA)

1 1 1Cristian Marunteanu , Mihai Mafteiu , Victor Niculescu1University of Bucharest, 020956, Romania (e-mail: )cristian@gg.unibuc.ro

belonging to the Transylvania basin. The medieval complex has been builtth thon the Citadel Hill in more stages between the 12 and the 17 century. Theth

fortified area and the ecclesiastic buildings from the 13-15 century and theth

buildings from the 15-17 century are still well preserved: the Clock Tower,the Furriers' Tower, the Butchers' Tower and Bastion, the Ropemakers'Tower, the Tinsmiths' Tower and Bastion, the Leather Dresser Tower, theChurch from the Hill, the Monastery Church, the Vlad Dracul House, etc.Some of them have been affected in the last years by instabilityphenomena, for instance the fortified walls, the Tinsmiths' Tower and Casa

thWagner, a building from the 17 century. Contemporary pictures of the areasare shown below (left and upper right figures).

Sighisoara is located in the southeastern part of the Tarnava plateau, The geological background is constituted of Pannonian sedimentary

deposits, represented by quasi-horizontal clays, marly clays and clayeysands alternating with fine to coarse sands. These deposits are coveredwith Quaternary deluvial formations and anthropogenic deposits, up to 9 mthickness.Morphologically, the Fortress Hill is a witness of Tarnava Mare river erosion.The maximum level of the hill is of 432 m, with a relative height of 80 - 85 m.The physical-geological phenomena that affect the medieval fortress hilloccur as shallow slides (lower right figure) and erosion gullies.

1. INTRODUCTION 2. GEOMORPHOLOGICAL CONDITIONS

n the covering deposits, the accumulations of the water provided by the rainfallstorages, the leakage from the supply and sewerage pipes or from cesspoolexfiltration and by the irrigation of the gardens produce an important reduction ofhe shear resistance of the soils and of the filling determining the slope instability.

Taking into consideration the geological, geomorphological, hydrogeologicaland climatic background and the identifiable human induced factors as mainconditions that cause landsliding, some elements of the landslide risk can beassessed:

- The Fortress Hill is not affected by large and deep landslides that couldendanger the general stability of the citadel;

- The landslides (active or semi-stabilized) have the depth of 2-4 m and thewidth of 85-120 m and affect only the covering deposits (deluvial or filling);

- The induced increasing of the humidity is considered the main cause of thenstability phenomena;

As a result of the geological and geoelectrical investigations (central figures)some mitigation measures have been proposed and taken in the view todecrease the risk of degradation or even destruction of this historical site ofSighisoara:

- Rehabilitation or repair of the supply and sewerage pipes and cesspools;- Consolidation of the towers and impermeability works of the pavements

around;- Rehabilitation of the medieval walls in the zone affected by landslides and

stabilization by retaining walls and counterforts.- Consolidation of the basement by under building of the vaults at a lowerlevel than the initial level and reinforcing of the new foundation by concretebeams;- Draining of the basement by gravel trenches.

4. RESULTS AND MITIGATION MEASURES

Basement ceiling

Fissures in walls

Old sewer pipes (-1.3 m)

New sewer pipes (-3.3 m)

Sewer High humidity zoneLithological limit inside PannonianLithological limit deluvium/PannonianGeotechnical limit filling/deluvium

IsoohmsVES locations (w20-w1)

Citadel Square

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Interpretative geoelectrical cross sections along the Casa Wagnerbuilding and yard a) 2002; b) 2005

Fortified wall affected by landslide Interpretative geoelectrical section Casa Wagner main facade

Instability phenomena on the slopes of the Citadel Hill

Contemporary picture of Casa Wagner

GG

Regional IAG/AIG Conference on Geomorphology: Landslides, Floods and Global Changes in Mountain RegionsSeptember 15-26 2008, Brasov, Romania

Fissures in the Tinsmiths Tower

3. LANDSLIDE RISK ASSESSMENT