# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines  
Some significant properties of DSs are their high porosity, high sorption potential [6; 33; 79], high initial void ratio, and low density [18; 19]. High liquid limit values have been identified in DS from Mexico and Japan [32; 40]. Void contents between 80 and 90% [65; 80] and specific surface areas between 40 and 350 m\({}^{2}\)/g have also been reported [32; 81]. The permeability coefficients of undisturbed DS have been recorded in magnitude of 10\({}^{-6}\) cm/s what implies an impervious layer [82]. However, there are few documentary sources in which physical properties are analyzed or identified as a function of frustule concentration, species, type, or state of deterioration such as \"crushing\" [7].  
Investigations have been carried out on the shear strength of kaolin and DS mixtures evaluated in undrained conditions [12] in order to determine the influence of the diatom fossil content on the resistant properties of this type of mixture, particularly regarding the angle of internal friction \(\phi\). \"For diatom additions between 40% and 60%, the increase is significant, 25.3% and 41%, respectively, at an overconsolidation ratio OCR = 1 and 33% and 45%, respectively, for an OCR = 2\" [32].  
The microscopic skeletons of algae and dead plankton in soils and sediments lead to the measurement of mechanical characteristics in magnitudes that contradict the behaviors defined in classical geotechnics [20] and this represents a lack of experience in their engineering properties [21]. The fluid retention potential and other properties are a function of the geometry and arrangement of the frustules and pores, which are dependent on the species and its homogeneity (single or multispecies condition) [25]. Diatom microfossils affect soil properties such as water content, Atterberg limits, and density because of the sizeable intraparticle porosity of the frustules [29].  
Soils containing diatoms have improved connection between microstructures, but due to the presence of expansive minerals such as illite or montmorillonite they may present expansivity problems [6,33]. Similarly, they can retain high water contents inside their frustules [18,22] and simultaneously register high friction angle and shear strength values [12,18,22].  
The results presented by [40] indicate significant increases in the permeability and compressibility coefficients of soils with diatom microfossil contents. Ref. [7] concluded that diatom microfossils in marine sediments contribute to increased slope stability under static and cyclic loading conditions because diatoms confer increased resistance for any loading mode. Such an increase is a product of particle entanglement and surface roughness.  
Additionally, several studies have been conducted to investigate the water retention curve of diatomites [17] and the cumulative effect of these on consistency limits. These increases are attributed to the enormous water-holding capacity of the internal structure of the frustules [32,40].  
The interest in microfossil deposits has reached the point of proposing modeling exercises to predict or correlate their behaviors with physical properties and mechanical responses. Ref. [67] evaluated the effects on the behavior of diatomaceous rocks under the \"strain-softening\" condition as a function of time. This aspect compares the results obtained in normally consolidated specimens and those obtained from the numerical simulation of undrained triaxial tests. Ref. [83] analyzed the effect of the intermediate principal stress on the strength of diatomaceous rocks under complex stress states. For this purpose, numerical simulations and triaxial tests in CU and CD conditions were compared using 3D finite difference codes.