# Diatomaceous Soils and Advances in Geotechnical Engineering--Part I
## 3 Review of Progress in Geotechnical Lines
### Compressibility in Diatomaceous Soils
It is proposed that the wide permeability at low levels of vertical stress allows for rapid drainage and the dissipation of excess pore pressure, which translates into a high degree of apparent overconsolidation. To this must be added the effects of particle locking and cementation, which also contribute to the overconsolidation condition described. Low levels of consolidation below 100 m are related to depositional sequences that have never experienced a dry condition or perceived a state of effective vertical stress. Situations like this generate contradictions between geologic evidence and laboratory data [44]. Microscopic observations carried out after compressional processes show high contents of frustule destruction, a phenomenon that could explain the wide ranges of compressibility recorded [18; 40]. Figure 13 presents the compressibility contrast (log Ov vs. e) of a series of DSs of different origins. For most species, the void ratio (e) variation ranges from 0.5 to 3.7. Two particular cases have been found for samples of Japanese origin (Centric monospecies) [40] and German origin (Remolded multispecies 100% DS) [44], which record initial values of e greater than 6.5. The North American multispecies report a maximum e of 1.9 for a concentration of 100% DS. For the case of the Colombian and Mexican monospecies samples with 60% DS content, maximum values of 1.87 and 3.67 were obtained, respectively [25]. In DS or samples with a high presence of microfossils, axial strains are simultaneously associated with pore pressure dissipation and particle breakage. However, it is challenging to quantify the individual contribution of each mechanism. Suppose that pore pressure within the sample is not measured in an oedometric test. In that case, it is not feasible to determine whether a specific part of the compression is associated with primary consolidation. In DS, particle breakage is expected to be enhanced when a particular level of stress is exceeded, which will depend on the stress history and diatom content. Cc values increase at higher fossil contents, and Cs values are relatively small [29]. The presence of diatom frustules in a soil mass can derive in delayed compressibility (no volume reduction since the skeletons assume the stresses, restricting strains) or in a sudden increase in compressibility once the yield stress of the microfossils is exceeded [69]. From the results of characterization and compressibility in diatomaceous soils in Bogota, it was possible to identify that high values of compressibility coefficient and void ratio are related to high diatomaceous contents and high LL. In this case, the ratio between the compressibility coefficient and the recompression coefficient is 7.6 [11]. For the case of Oita diatomites (Japan), the pore size distribution of unaltered and unconsolidated samples is practically identical to that recorded in hydrostatically consolidated samples with stresses of 500 kPa. This characteristic indicates that the structure remains almost invariant in the pre-yield state (<2100 kPa), explaining why the strain and strength of this highly structured soil are independent of the stress level when in the pre-yield state [24].