# Influence of the Diatomite Specie on the Peak and Residual Shear Strength of the Fine-Grained Soil
## 3 Results and Discussion
In the 100% kaolin mixture, the material presented a contractive behavior during the shear stage being very similar to a normally consolidated clay or, at most, a slightly over-consolidated clay, as was expected. The same phenomenon was displayed until reaching the combination with 40% diatomite and 60% kaolin, where the mixture began to reveal a dilatancy response, especially at the highest consolidation stress (i.e., 400 kPa). The above could be due to the presence of diatomaceous material which provided frictional properties to the specimens. The behavior at 400 kPa was that typically shown by a dense granular material. Figure 5: Illustrative example for shear stress vs. displacement curve. The same phenomenon was more noticeable in the diatomite-kaolin mixtures manufactured with Mexican diatomite content equal to or greater than 40%, where the behavior at stresses of 400 kPa was always revealing dilatancy. This may have been influenced by the microstructural configuration of the Mexican diatomite where the discs present could interlock more easily than the cylinders shown by the Colombian species. This is consistent with what has been found in previous studies [21]. In samples prepared with 100% diatomite, the dilatancy was also observed at a medium normal stress (e.g., 200 kPa) for both species. Therefore, it could be believed that, when the specimen has the presence of only diatomaceous material, the behavior is more similar to a dense or compacted granular material. Figure 7 reveals the failure envelopes obtained from the annular shear strength test for the peak shear strength resistance for both diatom microfossil species. With respect to the modified mixtures with Colombian diatomite, at low normal stresses, the shear stress  
Figure 6: Vertical vs. horizontal displacement for both species analyzed at 60% diatomite content. seemed to be very similar for any content of diatom. Meanwhile, with increasing normal effort, the variability tended to be slightly higher. Regarding mixtures manufactured with Mexican diatomite, more pronounced changes are noted from diatomite contents equal to or above 60%. The trend also indicates that, as the diatom content increased from 60% to 100%, the shear stress tended to increase, especially at high normal stresses. Comparing the results from both diatomite species, the peak shear strength was much higher when modifying the kaolin mixture with Mexican diatomite instead of Colombian diatomite, especially when the confined vertical pressure was higher and with diatom contents superior to 60%. To cite an example, Mexican diatomite 60% displayed increments of 116%, 33%, and 45% when compared to Colombian diatomite 60% on peak shear stresses at 100, 200, and 400 kPa, respectively. In the same way, Mexican diatomite 80% showed values of peak shear stress of 93.85, 154.36, and 279.32 while Colombian diatomite 80% presented values of 34.08, 81.64, and 161.83 at vertical pressures of 100, 200, and 400 kPa, respectively. These findings support the notion that the shape and the species of the diatomite influence the peak shear resistance of soil. Similar to peak shear strength, the residual shear strength for all diatomite-kaolin mixtures was obtained, as can be observed in Figure 8. It was evident that, as the residual shear strength was recorded at large displacements, the values attained would be lower than the peak shear strength. Nonetheless, similar trends were observed. Regarding mixtures modified with Colombian diatomite, at 100 kPa of normal stress, the results were very similar despite the diatom content. However, at large normal stresses, the variance among the mixtures was higher. On the contrary, mixtures with Mexican diatomite showed higher dispersion at 100 kPa and lower variability at 400 kPa. Adding Colombian diatomite, no clear improvement in residual shear stress was observed. Mexican diatomite denoted higher values of residual shear strength, especially with diatom contents equal to or higher than 60%, as was observed in the peak shear strength as well.