Propriétés géotechniques des marnes et argiles du trias supérieur de Lorraine

Abstract : This text briefly comments the geological history, mineralogy, stratigraphy and sedimentation of mudstones and marls from the Keuper Marl series of the eastern part of France. Geotechnical studies in England and also in France point out particular problems related to the overconsolidated structure of this material of Triassic age. A vide scatter in observed in the test results between the high values of strength of the unweathered soils and the low values of the softened zones. No simple relation to depth can be estahlished. A classification modified from the scheme proposed by the British research workers, shows that index properties and clay-sized proportion change with the alteration zones, as a result of silt-sized aggregation of clay minerals. Simple unexpensive tests allow quick quantitative evaluation of the unweathered material. Point load test and direct shear test on preformed failure planes give a measure of cohesion and ultimate friction angle. Short term weathering of marls appears closely related to the degree of saturation of the specimen before rewetting. One-dimensional and three-dimensional compression tests of intact and remoulded states are compared and the computed values of permeability from those tests are discussed. Rates of secondary compression are related of the alteration zones and overconsolidation ratio. Theoretical and experimental evidences lead the author to develop a graphical method of obtaining the strength parameters from stress paths in a three-dimensional (shear stress, normal stress, water content) space. Most of the scatter resulting from various swells during alteration, sampling and testing, is thus taken into account. The shape or the undrained compression stress paths correlates with the elastic parameters measured. Hvorslev strength components or Keuper clays and marls are compared with published data for other soils. Measurements of strength parameters by the static cone penetrameter in the weathered profile over Keuper Marl, are evaluated and compared with results obtained on a small-scale laboratory apparatus. The system was designed with a confinement cell (15 x 15 cm) which permitted to simulate the overburden pressure, up to 4 kg/sq cm. Finally, a regional study of 440 natural slopes shows a slight correlation with geology and index properties. Equilibrium conditions of natural slopes seem to be closer to the "critical state" strength envelope than to the residual angle.
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Marc Durand. Propriétés géotechniques des marnes et argiles du trias supérieur de Lorraine. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 1972. Français. ⟨NNT : 1972NAN10119⟩. ⟨tel-01754234⟩

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