# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines
### Shear Strength of Diatomaceous Soils  
DS can reach high shear strengths and large yield surfaces [18]. This is understood to occur because of the phenomenon called \"interlocking\" [5] and the high frictional component in the contact zones between particles that present rough surfaces and a high silica composition [35; 40]. The high \(\phi^{\prime}\) values of Japanese marine clays are due to the composition of clay minerals and the existence of granular materials, that include abundant diatom microfossils [87]. The variation in the arrangement of soil particles and the presence of microfossil fragments generate differences in the behavior of stress paths [87]. The frictional behavior of some diatomaceous deposits is mainly influenced by the size and shape of their particles [69]. An increase in diatomaceous content leads to an increase in the friction angle. In triaxial tests carried out in soils of Bogota in undrained conditions, the friction angle was recognized through the increase in the LL and organic matter content, a situation contradictory to that reported in the classical literature [11]. Classical soil mechanics leads to the assumption that the effective friction angle \(\phi^{\prime}\) of soil tends to decrease when the PI of soils is increased. However, in deposits containing diatoms, this projection is not fulfilled. Mexico City soils, although claycy, report \(\phi^{\prime}\) values of 40\({}^{\circ}\), even when the PI is close to 300%. The presence of microfossils (diatoms or others) can alter the resistant parameters, particularly the friction angle [8]. According to [32], the behavior of stress-strain curves depends on the content of diatoms. From this research, some of the properties of the volcanic lacustrine soil of Mexico City may be explained. The relationship between the internal friction angle \(\phi^{\prime}\) and the  
Figure 13: Compressibility in SD of different origin. Adapted from [25]. Ref. [25] ([PERSON] et al., 2021), Ref. [40] ([PERSON] et al., 2002), Ref. [56] ([PERSON], 2009), Ref. [18] ([PERSON] et al., 2019), Ref. [33] ([PERSON] and [PERSON], 1999), Ref. [19] ([PERSON] et al., 2018), Ref. [5] ([PERSON] et al., 2021), Ref. [10] ([PERSON] et al., 2021), Ref. [24] ([PERSON] et al., 2006), Ref. [24] ([PERSON] et al., 2006), Ref. [87] ([PERSON] et al., 2001), Ref. [29] ([PERSON] and [PERSON], 2019), Ref. [44] ([PERSON] et al., 2017). diatomite content is remarkable. The values of \(\phi^{\prime}\) for normal stress of 260 kPa were found to vary between 27\({}^{\circ}\) and 37\({}^{\circ}\). For a normal stress of 130 kPa, the values ranged between 25\({}^{\circ}\) and 38\({}^{\circ}\). From the evaluation of artificial mixtures of diatomite with Singapore clay and kaolin, it was possible detect an increase in \(\phi^{\prime}\) as the fossil content increased, particularly from 25%. At this dosage, the \(\phi^{\prime}\) of the mixture with kaolin rose from 24\({}^{\circ}\) to 34\({}^{\circ}\), and for the case of Singapore clay, the change was from 22\({}^{\circ}\) to 30\({}^{\circ}\). The above was without significant changes in the PI for concentrations lower than 75% [8]. The shear strength of DSs from Luneburg Heath, Lower Saxony, in Germany, was studied by the authors of [7] using direct shear tests under drained conditions on weight-dosed artificial samples (kaolin + DS), varying normal stresses between 200 kPa and 600 kPa. Increases in the effective friction angle \(\phi^{\prime}\) were observed going from 20\({}^{\circ}\) to 32\({}^{\circ}\) when the DS content increased from 0% to 100% for a normal stress of 400 kPa. The most significant gain in shear strength was observed for the 25% DS content. Some investigations have assessed the undrained shear strength (Su) in DS using Vane tests. This equipment is suitable for use in saturated fine soils in soft and stiff conditions. Particle sizes distinguish DSs in the range of salts and fine sands, which leads to partial drainage during shear tests.