Construction en pierre massive en Suisse

«For me, to build an air terminal with stone would be a stupidity, not to say a madness. But to use dynamic structures to fit three-roomed flats with kitchen in buildings from three to ten floors, is not less aberrant.»1 Provocation of a reactionary architect or a lucid analyze of the world of the construction of his time, this assertion of Fernand Pouillon still preserves, forty years after, its value of interrogation on the use of the natural stone. Indeed, since the industrial revolution and the introduction of new construction materials, like concrete and steel, the natural stone was gradually confined in the sphere of the noble claddings. If we look at behind, on the other hand, until the 19th century, we realize that the situation was very different, as well the use of this material as its social status. The stone was, and it still is, thanks to its great durability, the principal constituent part of the built environnement: public buildings, simple rural buildings, civil engineering works, cadastral limits and limits of properties, all were made out of natural stone, a material largely available locally, at least in our countries, and whose exploitation required reduced energy investments. The local builders knew, in an empirical way, the characteristics of the rocks they had as much to facilitate their extraction, by exploiting the natural fractures and "weaknesses", as for their selection. Thanks to their resistance to the atmospheric agents, increased by the strong thicknesses used, the cut stones could be employed again. The investment in work and energy was thus amortized on several generations. An adequacy between the resource, the exploitation and the techniques occurred naturally. In a slow evolution, the natural stone arrived until the industrialization of the processes of exploitation and shaping and allowed in France, in the years of the post-war period, to rebuild cheap blocks of flats by using a "pre-cut stone" with standardized dimensions. After the end of this "adventure", the use of natural stone in massive form slowly disappeared, to reappear in the years 1990, when the French architect Gilles Perraudin started to employ again dimensional stone, simply cut in the quarry, for the construction of buildings of various use. Our PhD thesis fit into the tradition of the experience of Fernand Pouillon. Indeed, today, at the era of sustainable development and the energy diaries, the use of natural stone as building material should be restored. Accordingly, we treat in this research the case of massive stone construction in Switzerland. While following the course which leads the natural stone of the mountain to the building, we tried to define a method to use dimensional stone in the current construction industry, while respecting the current constraints as regards durability, seismic safety and reduction of energy consumption. We thus tried to show that the natural stone can continue to be regarded as a whole construction material, and this by using the scientific checking, new in this form, of practices well consolidated by the centuries. In a restricted territory like Switzerland, all the principal families of rocks are present. The reduced distances make it possible to consider their use with regional scales, even national. The builder thus sees himself obliged to know their geological, petrographic and technical characteristics in order to be able to select them, since the properties of the material influence its behavior in the building as much at the static level as of durability, but also they determine the techniques which are employed to extract it from the deposit and to shape it. Indeed, before being employed, the rock must become dimensional stone: the exploitation of the quarry, its contemporary techniques as well as the various forms of shaping require to be known and analyzed. These processes do not influence only the dimensions of the stones, but their cost as much for energy as financial. In the second chapter of this research, we study the exploitation of the natural stone quarry. The empirical knowledge acquired during the field visits as well as the scientific data produced by the laboratory tests, that almost each producer currently has, enabled us to select the Swiss rocks for the massive construction and to collect them in all-encompassing cards. Moreover, the availability of natural stone is the essential condition to consider its use in the construction industry. The management and the restoration after exploitation of quarries are treated as much at the environmental level as of regional development. The knowledge acquired on the natural stones, their characteristics and their exploitation is used by the builder to define their use in building. This one does not follow simply from constructive or static criteria, but, today, also from seismic resistance, thermal comfort, lifespan and durability. We propose in our work to use the dimensional stone masonry for three types of constructions: load-bearing structure for buildings; self-supporting cladding for façades and load-bearing structure or cladding for retaining walls. In all these cases, we envisage that the project is carried out in an adequacy between the rock, its modes of exploitation and the current constructive requirements, in order to demonstrate the topicality of this ancestral material. ________________________ 1. Pouillon, F. 1968: Mémoires d'un architecte, Paris, Editions du Seuil, p. 174.

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