# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines
### Consistency and Plasticity in Diatomaceous Soils  
The high liquid limit (LL) values of soils or soil mixtures containing diatomaceous microfossils can be explained by the large intraparticle pores of the frustules, in which a large amount of water is stored. This intraparticle fluid is in addition to the pore space and does not affect particle-particle interactions [29]. In addition to the dosage, other properties affect index geotechnical parameters, such as the shape of the frustule, its porosity, and its preservation (whole or broken particles). Additionally, in the case of artificial mixtures, the mineralogy of the matrix, which can be kaolin type, will be influential [15]. Figures 8 and 9 show an increase in the consistency limits of different DSs as the fossil content increases, an aspect that has also been highlighted by [15]. These effects are particularly evident for the LL [19], in which similar positive slopes are observed for DSs of different origins. The Osaka sedimentary deposits in Japan [8] show a similar increase in their consistency limits, proportional to the microfossil content, while the plasticity index (PI) remains more or less constant [15]. Thus, it can be inferred that the index properties of DS samples alter as a function of the microfossil concentration. This aspect is due to the geometry and porosity of the frustules, which enhance the amount of water stored in the soil [8; 17; 18]. The high LL values can be explained by the frustules' high storage and absorption potential [6] on two scales. The first is in the total volume generated by the fossil (micro--dependent on the shape), while the second is in the volumes of the distinctive pores of the frustules (nano--dependent on the biological processes of the species) [43]. It is then posited that, although diatomaceous soil reports a high absorption level, water is encapsulated and does not affect the connectivity between the frustules or their fragments. Figure 10 shows the classification of some soils using the plasticity chart according to the concentration of fossils (by weight). In some Mexican and Colombian monospecies samples [12], the increase in the PI as a function of LL can be observed under a condition parallel to A-line. Conversely, almost perpendicular behavior concerning the A-line is evident in the monospecies samples from Japan [40] and Mexico [56]. The North American multispecies sample [25], although not entirely parallel to the A-line, retains an upward proportional behavior between PI and LL. \begin{table}
\begin{tabular}{c c c c} \hline
**Origin** & **Type** & **Gs** & **Source** \\ \hline Mexico & Not defined & 2.72–2.80 & [41] \\ Chile & Centric monospecies & 2.63 & [22] \\ Indonesia & Not defined & 1.87–2.00 & [55] \\ Japan & Not defined & 2.40–2.70 & [56] \\ Mexico & Centric monospecies & 2.32–2.35 & [56] \\ Mexico & Not defined & 2.6 & [79] \\ USA & Monospecies & 2.08 & [20] \\ USA & Multispecies & 2.29 & [25] \\ Mexico & Monospecies & 2.34 & [25] \\ Colombia & Monospecies & 2.55 & [25] \\ USA & Multispecies & 2.20–2.57 & [5,10] \\ Japan (Ishikawa) & Not defined & 2.183 & [86] \\ Japan & Centric monospecies— & 2.13 & [24] \\  & Cyclotella & 2.183 & [67] \\ Not defined & Diatomaceous Luitte & 2.51 & [85] \\ Colombia (Dosquebradas) & Monospecies & 2.45 & [85] \\ Colombia (Siachoque) & Monospecies & 2.43 & [85] \\ Colombia (Chivata) & Monospecies & 2.43 & [85] \\ USA & Not defined & 2.2 & [15] \\ \hline \end{tabular}
\end{table} 
Table 1: Specific gravity values in SD according to origin and type. In classical soil mechanics, a higher value of PI in the soil is associated with lower shear strength. However, this phenomenon is the opposite in DSs; due to the record of increments of PI because of the water storage potential, they also tend to register a higher value of friction angle as the fossil content increases [18]. Ref. [14] proposes that the Casagrande Chart is suitable for classifying kaolin-type or diatomaceous-type soils when these have a total concentration--i.e., 100% for either of them.