# A Procedure to Prepare Sand-Clay Mixture Samples for Soil-Structure Interface Direct Shear Tests
###### Abstract  
A large number of experimental studies on sand-clay mixtures are well documented in the literature; however, the preparation protocol is rarely clearly detailed or varies a lot according to the authors. Variations in the preparation technique obviously increases the challenge of comparing different test results. As a consequence, sample preparation for sand-clay mixtures should be kept as constant as possible to ensure homogeneity and uniformity of samples and limit result variability. This paper develops a detailed procedure on how to prepare sand-clay samples for interface direct shear tests. Sand-clay mixtures are prepared with Fontainebleau sand, kaolinite clay and distilled water by the S1 (sand-water-clay) protocol. The uniformity of the reconstituted specimens is assessed by measuring the water content and density on three slices from the top to the bottom across the specimens. The repeatability of the samples is checked with oedometer and interface direct shear tests. This sample preparation procedure can be used for preparing sand-clay mixture for interface direct shear tests to investigate the influence of clay content or other effects (e.g., temperature) on the mechanical behavior of soil-structure interface. It has demonstrated great performance in preparing samples with good homogeneity and shape, compared to other traditional reconstitution techniques. With the sample preparation procedure, we can obtain repeatable test results as well. s +
Footnote †: journal: Applied Sciences  
0000-0001-7000-00001-7000]J.J.L.L.L. 0000-0001-7000-00001-70000]J.  
their intrinsic properties, especially heterogeneity, anisotropy, and the geological history among others [32; 33; 34; 35]. The complexity of soil specimens can therefore sometimes lead to inconsistent testing results, which increases the challenge to determine a finite set of intrinsic parameters characterizing their main features. Experimental and theoretical studies of soil behavior have often concentrated on ideal soils (pure clays or uniform sands), and soil mechanics have mainly been developed based on the test results of pure sand or pure clay [7; 13; 17; 18; 23; 36]. However, as mentioned above, natural soils usually consist of coarse granular grains in a matrix of silt or clay. To better understand the mechanical behavior of natural soils, simplified and controlled soils are often used in laboratory testing instead of natural ones. The simplified soils can be reconstituted sand-clay mixtures with fabric similar to natural soils. The properties of such simplified mixtures are, thus, expected to be intermediate or transitional between the properties of the constituent materials (i.e., sand and clay). Although there are a lot of studies on sand-clay mixtures [37; 38; 39; 40; 41; 42] and on the interface for typical sand or clay [7; 8; 9; 14; 17; 19], there is a lack of data on the interface mechanical behavior between sand-clay mixtures and structure materials. Particularly, information is missing on how the clay content influences the interface direct shear behavior, i.e., shear strength, volumetric deformation, interface friction angle, adhesion, etc., and how the particles arrangement changes with changes in the clay content. These questions are significant for geotechnical engineering design since they play a critical role in the bearing capacity, the deformation and the failure of foundations [17; 43; 44], therefore implementing interface direct shear tests on sand-clay mixtures with different clay content is necessary to better understand natural soil-structure interface problems. Sample preparation is a key factor that influences the mechanical behavior of reconstituted soils in laboratory experiments [33; 45; 46; 47; 48; 49; 50]. This effect becomes more prominent for sand-clay mixture samples due to the clay fraction within the mixture.