habitat rupestre.pdf - Società Friulana di Archeologia

TURQUANTCRHIMA-CINP projectstruction of the Loire valley chateaux (having been left forseveral years in the river Loire to wash out their saltpetre) aswell as all the housing in the region. These quarries, on completionof extraction (15th century) left cavities that were firstlived in by the quarrymen, the “perreyeux”, and were oftenthe reason for the development of horizontal troglodytism inthe hillsides.- Vertical troglodytism developed on the plateau: on a sitewithout any particular relief, a hole is excavated forming aquad (“carrie”) with an access ramp. Walls are then cut out tocreate a habitat and outhouses, such as those to be found in thetown of Rochemenier.Fig. 3 Troglodytism in the Loire Valley, L. Triolet, 2001Fig. 4 General geological structure of the Loire, P. Fenelon, 1978Fig. 5 Plan map prevention of natural risksFig. 6 The perimeter of the site World Heritage of Unesco, Regional NaturalPark Loire-Anjou-Touraine3. Risks linked to geology: instability of the terrainIn Maine and Loire, there are a large number of undergroundcavities (all anthropic). An inventory of these cavities was carriedout in 1996 and updated in 2010 by BRGM to establisha risk map. This study revealed that 47 towns in the Saumurregion had 13,836 cavities and 14,000 access points (non-exhaustiveinventory).These cavities had either been dug out inorder to use the extracted material (mine, quarry) or to usethe created space (habitat, cellar, basement, etc.). The majority(11,120) are in sandy chalk and 2,300 in shelly sand. Thepresence of such a large number of cavities raises the generalproblem of the stability of the terrain given that sandy chalkthat is particularly liable to deterioration.The Saumur plateau (south bank of the river Loire) is aspecific caseThis hill is a sandy chalk escarpment, a vertical cliff facieswith a 30 metre amplitude. The destabilisation of the voids iscomplicated here by the natural deterioration of a hillside withno slope (“poussée au vide”) and its crumbling. There can alsobe a combination of the two phenomenon: collapse of the cavitiesand crumbling of the hillside. This is what happened inSaumur in 2001 with the collapse of the hillside under the chateauramparts leading to considerable material damage.The troglodytic habitat that developed in this region is subjectto the risks of this geology which can make it dangerous.There are two types of degradation processes that come fromeither inside or outside the cavities.Inside: improper sizing of the works during its creation, subsequentdestabilising works, lack of supervision and maintenance,considerable temperature variations via accesses notclosed off and causing freezing/unfreezing of the rock resultingin cracks.Outside: the permeability of the limestone can permit infiltrationof rainwater or water from ditches which then tunnelsthrough to create underground networks. Surface plants canhave roots that penetrate the rock, making it more fragile.These factors, alongside overstressing, the weight and vibrationsof surface level circulation, etc. can cause rockfalls, collapse,subsidence or the slipping of the hillside.TURQUANT: an arts and crafts villageWithin this context, we have studied the village of Turquantwhere the community has chosen to enhance its troglodyticheritage.Located to the eastern extremity of the Saumur hillside, Turquant,a village of 550 inhabitants, has 480 listed cavities that,volumeRicerca_OK_2012-11-15.indd 134 16/11/2012 15:02:16