RésuméL'état de contraintes actuel, dont la modification anthropique ou naturelle entraîne des déform ations, éventuellem ent des désordres, est un d es élém ents essen tiels de la reconnaissance d'un terrain. Sa détermination fait appel à des bases théoriques et à l'expérimentation. Dans la prem ière partie, outre quelques rappels bibliographiques concernant les cham ps théoriques pour des surfaces topographiques planes ou diédriques, est introduit le tenseur (K0) qui se ramène au scalaire k0 dans le cas du milieu pulvérulent.
AbstractThe actual state of stresses, of which the anthropic or natural modification drags some distortions, is one of the essential elements of the soil recognition. Its determination calls on theoretical bases and experimentation. In the first part, besides some bibliographic recalls concerning the theoretical fields under plane or diedric topographic surfaces, the tensor (K0) is introduced that reduces to the scalar k0 for granular media. The surface tensor (Σ o leads to a new definition of k0 for cohesive media. An original elastic analytical study is also proposed for valleys in « U » and « V » and massifs in « spur » or « needle » shape.
37The second part is about realistic reliefs (vallev. mountain or combined) using numerical modelling. Some examples are presented showing the isostatic lines and, on a vertical isostatic, the variations of the main vertical and horizontal stresses (σv and σ11). The effect of a « tectonic » lateral tightening is analyzed. The third part deals with recent returns of French experience; it confronts analytical and numerical results with field measurements. The East of France is concerned with a regional extension that may even appear in surface by a main minor negative stress (traction). In the case of the Alps, the topographic and tectonic effects are sensitive : i) slant of the principal reference axes under the sides (parallelism between relief side and major isostatic); ii) concentration of the horizontal stresses under the valleys (often perpendicularly to these); iii) for the vertical stresses: « heaviness effect» under the valleys and « lightness effect » under the mountains.