# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines
### Shear Strength of Diatomaceous Soils
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Origin** & **Soil** & \(\Phi^{\prime}\) & **Recorded stress** & **Author** & **Comments** \\ \hline \multicolumn{6}{c}{Consolidated undrained triaxial tests. From the graphical representation between confining stress and undrained shear strength, an inflection point is identified at 1550 kPa. When the confining stresses are lower than this transition point, the undrained shear strength is independent of the confining stress and is more related to the structural strength of the diatomic. When the confining stress is greater than the transition stress, the undrained shear strength increases linearly with the confining stress. \\ \hline \multicolumn{6}{c}{Subhorizontal laminae and other non-organic microstructural elements (microdisonal skeleton) are reflected in the high values of \(\Phi^{\prime}\) of organic soils. The deformation mechanisms of microstructural elements explain the unusual geotechnical properties. Despite the dispersion in index properties, organic soils exhibit extremely high values of \(\Phi^{\prime}\) during triaxial CU compressions. These values are associated with low effective confining pressure. \\ \hline \multicolumn{6}{c}{Shear test results show a strong microstructural connection in the Tengchong diatomaceous day soil, which is different from that in common soft clay rocks. It exhibits elastic deformation under confining pressures between 100 kPa and 250 kPa. However, under a pressure of 400 kPa, obvious plastic deformation is observed, indicating that the internal microstructure is destroyed. Consolidated drained triaxial test.} \\ \hline \multicolumn{6}{c}{The friction angle increases as the liquid limit increases (linear relationship) and can reach values as high as 47\({}^{\circ}\). The high \(\Phi^{\prime}\) can be explained by the presence of diatoms. Consolidated undrained test.} \\ \hline \multicolumn{6}{c}{The differences in \(\Phi^{\prime}\) of the soil mixtures (kaolin + DS) have a clear link with the shear strength of pure diatoms, evaluated through their angle of repese. These differences are certainly related to their shapes. The cylindrical condition of Aulosae (Colombian origin) reduces the interaction between particles and allows the particles to roll, while the high angularity and interlocking of Cosolaciousae particles. Consolidated undrained test.} \\ \hline \multicolumn{6}{c}{The soil behaves slightly dilatant at confining pressures below 100 kPa and highly contractive at pressures above 100 kPa. The resistance can be controlled by the microstructure of the soil, influenced by the rearrangement and breakage of diatoms, creating a transition to a frictional behavior. Soil heterogeneity due to diatom layering implies a high variability in triaxial shear tests at confining pressures above 500 kPa. Compared to conventional fine soils with similar PI, the cyclic behavior of diatomico souli is more brittle at low stresses, but degradation is greater at high stresses. Isotropically consolidated undrained tests.} \\ \hline \multicolumn{6}{c}{The Buck Creek deposit exhibited unusually high shear strength, considering the elevated porosity, plasticity, and compressibility records. This is attributed to entanglement between diatom particles. The undrained shear strength from the effective friction angle is found to be high, but lower than that calculated using SPT-type procedures. Isotropically consolidated undrained tests.} \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._Under the shear ring method, Ref. [89] evaluated samples of unaltered diatomaceous clay extracted from the Shambsk sector in Armenia, applying normal pressures of 0.5, 1.0, and 1.5 kg/cm\({}^{2}\) and shear stresses of 0.50, 0.45, 0.40, and 0.35 kg/cm\({}^{2}\). The latter was kept constant for up to 200 days and in conditions close to the degree of saturation. For all cases, the angle of internal friction varied between 27\({}^{\circ}\) and 33\({}^{\circ}\). It could be concluded that Shambsk diatomaceous clays do not show expansion potential.