# Influence of the Diatomite Specie on the Peak and Residual Shear Strength of the Fine-Grained Soil
## 2 Materials and Methods
### Annular Shear Strength Test  
The annular--or the ring shear strength test, as it is also commonly known--was employed in the current study to measure peak and residual strength of the diatomic-kaolin mixtures. It is worth pointing out that estimating the peak and the residual strength is extremely important to find out the limit states of a material or a geotechnical structure, due to the fact that they present different levels of strains and stress paths. For instance,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample N\({}^{\circ}\)** & **Id Mixture** & **Composition** & **Liquid Limit** & **Plastic Limit** \\ \hline
1 & Kaolin 100\% & 100\% kaolin & 44 & 24 \\
2 & Col. Diatomite 20\% & 80\% Kaolin-20\% Colombian diatomite & 50 & 28 \\
3 & Col. Diatomite 40\% & 60\% Kaolin-40\% Colombian diatomite & 56 & 32 \\
4 & Col. Diatomite 60\% & 40\% Kaolin-60\% Colombian diatomite & 70 & 38 \\
5 & Col. Diatomite 80\% & 20\% Kaolin-80\% Colombian diatomite & 83 & 42 \\
6 & Col. Diatomite 100\% & 100\% Colombian diatomite & 99 & 48 \\
7 & Mex. Diatomite 20\% & 80\% Kaolin-20\% Mexican diatomite & 49 & 28 \\
8 & Mex. Diatomite 40\% & 60\% Kaolin-40\% Mexican diatomite & 56 & 34 \\
9 & Mex. Diatomite 60\% & 40\% Kaolin-60\% Mexican diatomite & 80 & 45 \\
10 & Mex. Diatomite 80\% & 20\% Kaolin-80\% Mexican diatomite & 110 & 50 \\
11 & Mex. Diatomite 100\% & 100\% Mexican diatomite & 132 & 60 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mass ratio in percentage of the mixture designs.  
Figure 2: Particle size distribution.  
in terms of design, an excavation supported by a retaining structure could present two situations. On the one hand, the soil subjected to a passive condition could reveal small strains reaching its peak resistance. On the other hand, the soil mass supported by the retaining structure could already be subjected to large strains and, therefore, be closer to its residual strength.  
To perform the test, the reconstituted humidified diatomite-kaolin specimen was removed from the plastic bag and placed in the annular shear cell. The annular shear cell consisted of two concentric rings confined vertically and totally filled with water. Then, normal stress was applied to the sample by the top plate by means of a lever-arm (see Figure 3). Similar to the consolidation test, the samples were consolidated by performing the water pore pressure. Once the mixture was consolidated, the shear strength was measured. To shear the sample, the upper lid and the bottom ring must rotate relative to each other. In that sense, the bottom ring rotated at a controlled angular speed whereas the upper part was restrained by a horizontal beam, and a torque cell device helped to measure the shear resistance of the soil. Both the normal stresses applied on the lever arm and the measured shear stress were previously calibrated to avoid measurement errors. To obtain drained conditions of the test, this was carried out at an angular speed of 0.032 radians per second. The normal stresses to which the samples were consolidated were 100, 200, and 400 kPa, respectively. The vertical displacement was also recorded to analyze the specimen volume change. More details of the procedure are described in the United States Bureau of Reclamation USBR 5730.