# Influence of the Diatomite Specie on the Peak and Residual Shear Strength of the Fine-Grained Soil
## 3 Results and Discussion  
Initially, to have more comprehensible knowledge with respect to the diatomite-kaolin mixtures, the Afterberg limits for the different diatomite concentrations were recorded, as shown in Figure 4. Although it is very typical to obtain the \(LL\) of the samples by applying the [PERSON]'s method, in this research, the fall-cone method was adopted since the calculations for Mexican species was not possible with the conventional method. As can be seen in the Figure 4, the trend suggests that the higher the diatom content was, the higher was the increase in liquid and plastic limit. This result ties well with previous studies wherein limit and plastic limits increase with the increase in diatomic content [9]. An explanation of the above could be that the hollow structure and the pores along their surfaces help to retain more water, increasing their Atterberg limit values. Concerning the type of diatom species, the Mexican displayed higher values of both liquid and plastic limits in relation to Colombian species. In agreement with the above, the Mexican species displayed a lower specific gravity than the Colombian species, indicating that this species could present higher porosity and, as a result, retain more water inside its structure. Figure 3: Annular shear strength test. Adapted from [18]. Concerning the shear resistance, the annular shear test presents a particular advantage over other kinds of shear tests (e.g., direct shear) considering the possibility to evaluate the residual strength parameters in the same fail surface and in the same shear stress direction because of the radial movement of the soil container. The residual shear strength is a property of fine soils which evaluates the gradual loss of shear strength along a developed failure surface and, thus, in some cases, it is better to use this value rather than peak shear strength for design purposes. For all diatomic-kaolin mixtures, the shear-strength vs. displacement curves at the three normal stresses were calculated. Figure 5 shows the results of shear strength vs. displacement for the two diatomic species under study. The increase of diatomaceous material in the mixtures with kaolin revealed slight increases in resistance. Regarding the stress-strain response, it is noted that the shear stress increased in those specimens subjected to greater consolidation steps. Besides, at higher normal stresses, the behavior of the curves looked more typical of a compacted sand than of a normally consolidated clay, especially with higher contents of Mexican diatomite. Unlike clays, the fossilized diatoms did not present electrochemical properties; thus, the improvement in the shear stress could be attributed to the friction produced between the particles. The above is because the higher the diatomic content was, the greater the shear resistance was. With some exceptions, the residual shear stress was kept constant after reaching 4 mm of horizontal displacement. A point of interest worth highlighting is that, for all the samples, regardless of the stress level and the amount of diatomic added, they adequately reached the critical state of the soil during the residual condition of the material. This concept is fundamental to understand the response of the soil that has been previously remolded, as it was in the current case, where the specimens underwent a previous peak resistance [19,20]. Figure 4: Liquid limit (LL) and plastic limit (PL). To analyze the volumetric behavior of the diatomite-kaolin mixtures, the vertical displacement was also recorded for all the specimens, as can be observed in Figure 6. From the graphs, two important aspects were deemed for analysis: firstly, the deformability observed in the specimens when they were subjected to different consolidation stresses prior to the torque shear stage and secondly, the behavior observed in the composite material by the influence of diatomite.