# 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 elaboration of artificial soils from kaolin has even been utilized to evaluate models of materials subjected to geotechnical centrifuge tests due to its versatility in preparation, handling, and consistency. In addition, its mechanical properties mean that its response to load stresses does not differ from the behavior recorded in natural samples [92,93]. Although kaolin-based artificial soils are not a perfect substitute for diatomic, their use has made it possible to identify the impact of each component of the mixture on its physical, chemical, and mechanical properties. Changes in the geotechnical characteristics of the soils due to the presence of diatom microfossils were examined in [40] using artificially prepared mixtures. The clay used for the mixtures was kaolin, which is commercially available in Japan and has been used as a model for making mixtures with diatoms and crushed sand for comparative purposes. Mechanical mixing considered the application of distilled water. The mixing proportions used for of diatoms in the total mixture were 0, 25, 50, 50, 75, and 100%. The results indicated that the presence of microfossils alters the soils' index properties and other engineering properties. Refs. [33,87] show that the marine clays of Japan contain significant proportions of diatoms. The effects of these fossils have been assessed through tests carried out on mixtures of diatomites and kaolin [40]. One of the conclusions of these studies was that incorporating diatoms into kaolin matrices or clays such as Singapore clay leads to a reduction in soil density and a significant increase in \(\phi^{\prime}\) values [87]. Similarly, in artificial mixtures of kaolin and diatomite dosed by weight (0, 25, 50, 50, 75, and 100%), the authors of [8] managed to establish that LL and PL increase almost in the same proportion as the diatomic content increases. In one study, oedometric tests were conducted on pre-consolidated specimens of artificial kaolin-diatomite samples dosed by weight (40%) and on samples conformed only by fractured diatomite [29]. The results indicated that vertical strains derived from mechanisms other than primary consolidation in soils with diatomaceous microfossils depend on the level of effective vertical stress applied. In order to evaluate the influence of diatomaceous microfossils on the cyclic behavior of the soil, the researchers in [56] performed a series of pre-cyclic monotonic, cyclic, and post-cyclic monotonic tests on artificial kaolin-diatomite mixtures under simple shear conditions at a constant volume. The proportions of diatomite used were 0, 20, 40, 60, and 100% by dry weight. The tests were carried out under normally consolidated (OCR = 1) and preconsolidated (OCR = 2) conditions. The percentage of water added to the mixtures was equal to their LL. The results indicated that the cyclic behavior of the kaolin-diatomite mixtures depends on the stress ratio used, the level of strain reached, the OCR, and the diatomite content. The kaolin used by [56] is commercially distributed in Mexico; its kaolinite content was determined from X-ray diffraction and reported a value of 97%. The Gs and specific surface area were 2.57 and 22 m\({}^{2}\)/g, respectively. About 65% of the particles that compose it are smaller than 2 um in size, and its pH value is close to 5.8. This kaolin has an LL of 56% and a PI of 28% [56]. Ref. [32] evaluated artificial diatomite-kaolinite mixtures by simple shear under undrained conditions to determine the fossils' influence on their strength. The mixtures had proportions of dry weights of diatomite of 0, 20, 40, 60, and 100%. It was concluded that the strain needed to reach the maximum shear stress and friction angle and the Atterberglimit increases as the diatomic content becomes higher. The shrinkage of the mixtures and the PI decreases as the content of frustules increases. Variations in fabric, chemical stability, water holding capacity, and silica dissolution in mixtures of kaolin and diatomaceous earth were investigated by [20].