# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines
### Artificial Soils and Control of Variables in Diatomaceous Soils
The clay used in this research was untreated kaolin washed with sodium chloride solutions to change the surface electrical charge. The kaolin particles were dish-shaped and smaller than the diatomaceous earth particles. The Gs of kaolin was 2.6, and its specific surface area was calculated to be 40.4 (m\({}^{2}\)/g) [20]. While the diatoms presented internal porosity, the kaolin particles did not register any opening. It was concluded that the presence of diatoms significantly impacts the general behavior of soil mixtures due to the variation in the concentration of ionic pore fluid and the conformation of a more rigid skeleton that reduces the tendency of the soil to strain. The presence of diatoms in the mixture caused a decrease in coagulation in the presence of salt, increased LL and PL, increased water holding capacity, and reduced solubility in electrolytic solutions [20]. Experimental programs based on oedometric tests were developed by [79] using artificially prepared mixtures of diatoms and kaolin in order to evaluate the influence of microfossils on soil compressibility. The results showed that the compressibility of kaolin increases with the addition of diatomic, and, consequently, the Cc values for mixtures with diatomic are higher than those obtained for pure kaolin. In this investigation, dry kaolinite powder and diatomic were mixed gravimetrically then homogenized, and distilled water was added until the LL was reached. No segregation was observed during the process. An experimental program was developed to determine the influence of microalgae on kaolinite soils in one study [17]. Artificial samples with different contents of fossilized microalgae were prepared. The clayey base material used for the investigation was kaolin; some of the characteristics of this were LL: 63%; PL: 30%; and Gs: 2.65. The proportions of fossils were 5, 10, 20, and 40% by weight. It was concluded that the hydraulic properties of kaolin increased as the proportion of micro-fossilized skeleton related to higher diatom content increased. In order to identify the relationship between the microscopic and macroscopic characteristics of DSs, the authors of [12] prepared artificial mixtures with two species of diatoms, kaolin and drinking water. Some of the characteristics associated with the kaolin used were density: 2.69 g/cm\({}^{3}\); LL: 44%; PL: 24%; fraction <2 um: 29.1%; and d50: 10.5 um. From microscopic observations, it was determined that the kaolin platelets were not small enough to fill the nanopores characteristic of diatom frustules. Based on the mixtures, oedometric and triaxial chamber shear strength tests were developed. This study demonstrated the effects of the microscopic forms of the frustules present on the macroscopic responses of the soils. For the diatom species Coscinodiscus (discoid shape), an increase in the friction angle was reported, reaching values up to 51\({}^{\circ}\) for a fossil content of 60%. Meanwhile, for the same proportion of diatoms for the species Aulacoseira (cylindrical shapes), the friction angle reached was 34\({}^{\circ}\). The differences in the friction angle of these mixtures have a clear link with the shear strength of the pure diatoms, evaluated through their angle of repose. The cylindrical shape of Aulacoseira reduces the interaction between the frustules and allows them to roll, while the high angularity and interlocking of the Coscinodiscus increase the friction between particles [12]. The influence of two diatom species and their contents on the peak and residual shear strength in artificial mixtures of kaolin and DS were investigated in one study [37]. The kaolin used was untreated and commercially available in Bogota (Colombia). A Gs of 2.69 was reported. According to scanning electron microscope images, kaolin is composed of overlapping laminar groups and does not feature pores in its internal structure. The applied distilled water content corresponded to LL.