# A Procedure to Prepare Sand-Clay Mixture Samples for Soil-Structure Interface Direct Shear Tests
## 3 Reconstitution Procedure
### Requirements of the Sample Preparation for the Shear Box  
The dimensions of the reconstituted sand-clay mixture samples should have definite restrictions due to the dimensions and shape of the interface direct shear box. In this paper, the required dimension (100 mm \(\times\) 100 mm) of the sand-clay mixture sample was quite large in comparison to those in classical direct shear tests (e.g., 60 mm \(\times\) 60 mm). Particular attention must be taken during sample preparation to avoid working with unconsolidated soil samples, which may lead to leakages from the space (0.1-0.6 mm) between the upper and bottom parts of the shear box (see Figure 3). The sample must be preconsolidated before putting it into the shear box, it must be the least viscous possible and must have a planar surface for the piston to stay correctly in contact with it. Moreover, the sample must be as homogeneous as possible.  
All these requirements necessitate a non-trivial protocol for the sample preparation. Three different mixing orders of the soil components were studied. Also, considering the large size of the sample (100 mm \(\times\) 100 mm), a sufficiently large cylindrical consolidated cell had to be developed (with a diameter at least of 141.42 mm) to ensure proper preconsolidation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**K Clay Content (\%)** & **25** & **50** & **60** & **75** & **100** \\ \hline Liquid limit (\%) & 17.93 & 22.41 & 26.77 & 31.01 & 37.30 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The liquid limit of sand–clay mixture as a function of clay content.  
Figure 3: Improper sample preparation brings about soil specimen leakage from the space of the interface direct shear box: (**a**) leakage on the left of the shear box, (**b**) shear box and container, (**c**) leakage on the right of the shear box, (**d**) leakage in the front view, (**e**) soil sample without a good shape after dismantled and (**f**) soil leakage around upper part of the shear box.  
Figure 2: The SI mixing scheme: sand-distilled water-clay.  
The oedometer test was first performed, then the specimen was trimmed and put into the direct shear device. In our case, it was not possible to use the sample with the same shape for both preconsolidation and interface tests, the sample should be trimmed to fit the interface direct shear box. The conventional cylindrical oedometer cell (with a diameter of 70 mm) is smaller than the squared interface shear box (100 mm \(\times\) 100 mm). A new cylindrical cell was thus required, having a larger diameter than the diagonal of the shear box. A new oedometer cell was designed and manufactured for the sample preconsolidation, as shown in Figure 4. The designed oedometer cell consisted of a piston with small holes (7 mm in diameter), a cylindrical cell of stainless steel, two porous stone discs, a cap, and a base. These parts were fixed with some bolts after installation. The inside diameter of the cell was 150 mm, which is larger than the squared shear box diagonal (141.42 mm). The other details and dimensions of the designed preconsolidation cell can be referred to in Yin [57].  
This cell was calibrated with an oedometer test on Fontainebleau sand. The results were compared and validated with the test results of the classical standard oedometric cell. The validation showed that the cell worked well and had consistent results with the classical cell.