Effect of Sample Size on the Behavior of Granular Materials

Abstract

International audienceNatural soils or coarse granular materials containing large particles such as rockfill or ballast are often an issue for geotechnical projects. However, since it is usually complicated or impossible to set up a big enough experimental apparatus to test these materials, their mechanical behavior remains poorly known.To circumvent this difficulty, we have developed a set of triaxial cells of various sizes to study the experimental behavior of granular soils containing particle sizes of up to 160 mm. This paper presents the first results of a two-part experimental study. The first part consists of triaxial tests on sand samples of different sizes in order to examine specimen scale effects. Pre-peak behavior is not affected by the specimen size, whereas post-peak behavior depends on the test conditions that control the development of strain localizations. In the second part, we present drained triaxial compression tests on large samples of calcareous rockfill materials that have parallel grain size distributions.The results show a nonstandard evolution of the friction angle in relationship to grain size if compared to similar studies on coarse granular materials. Although grain crushing occurs during compression, the strain-stress curves of the different materials with different grain sizes do remain close. We explain this phenomenon by the strength evolution of the individual grains with respect to their size

A peek into the origin of creep in sand

“…We select 1D loading for simplicity of the experimental setup, for the relative ease of reaching stress levels greater than 1 MPa and because the cylindrical specimen shapes are convenient for X-ray tomography. In order to minimise scale effects, (see, for example, Hu et al [11]), the sample diameter is chosen such that the sample diameter is considerably larger than the mean grain size . The sample is prepared with a zero drop height, and the top surface is compacted with the loading ram in order to assure a horizontal surface.…”

Strain localization in the standard triaxial tests of granular materials: Insights into meso‐ and macro‐scale behaviours

“…As a result, several researchers have experimentally demonstrated that yield locus and stress-strain responses interpreted from the conventional triaxial tests were noticeably dependent on the sample scale. [15][16][17][18] When shearing takes place in the conventional triaxial test, soil specimen often deviates from homogeneity to inhomogeneity. The transition from an equilibrium state toward another mechanical state is accompanied by the development of kinetic energy.…”

Experimental Studies of Scale Effect on the Shear Strength of Coarse-Grained Soil

“…For instance, Gupta et al [10], Li et al [11], and Kim et al [12] support that the internal friction angle ϕ increases with the improvement of d max . On the contrary, Lee [13] and Hu et al [14] believe that the maximum particle size d max has little effect on the peak internal friction angle ϕ. Xu et al [15], Wei et al [16], and Simoni et al [17] found that the internal friction angle increases with the reduction of content of fine particles, and Li et al [18] observed that when the fine particle content is relatively low, the internal friction angle is stable at a certain level; however, after that, it decreases rapidly with increasing fine-particle content.…”