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Description
Earth-filled embankments, dykes, dams and their foundations are often built with coarse soils. These soils are characterised by a very widely graded particle size distribution and the presence of large particles. To characterise the mechanical behaviour of this type of soils, a triaxial bench was developed to test samples with a diameter of 300 mm and a height of 600 mm. In addition, a methodology has been developed to place an undisturbed sample with a diameter of 200 mm in a triaxial configuration. However, some soils may contain grains larger than 50 mm, which requires scalping procedures (granulometric reconstitution) due to the presence of oversized particles with respect to the size of the test device. Our work in partnership with Verbund and EDF aims to study the consequences of two scalping procedures (simple scalping and substitution) on the mechanical properties of coarse soils. For simple scalping, the oversized fraction is removed and replaced by an equal mass of finer materials.
Using the Discrete Element Method (DEM), numerical samples constituted by granular mixtures with discontinuous particle size distributions are tested. Experimental triaxial compression tests are also carried out on mixtures of glass beads, sand and gravel using triaxial devices of different diameters from 50 to 300 mm. The numerical and experimental samples are scalped and substituted. The density is controlled using different soil compactness parameters. The influence of the percentage of fines, particle size distribution and the properties of the replacement materials is studied.
The results show that simple scalping leads to an overestimation or underestimation of mechanical strength, depending on the original fine content and the choice of soil density control parameter. The effect of substitution on the mechanical characteristics of coarse soils stems from the reduction in the particle size distribution of the coarse fraction. Furthermore, it has been shown that an overestimation, a correct estimation or an underestimation can be obtained depending on the strength properties of the particles of the material replacing the non-admissible fraction. Based on the results, some recommendations are proposed to limit the differences in shear strength between scalped soils and original ones.