Intrinsic Compression Behavior and Microstructure of Soft Clay with Diatom Inclusion Effect

Soils containing diatom microfossils belong to biogenic sediments as lacustrine and marine facies, depending on the depositional settings and diatom species. The microfossil, a special biogenic mineral, endows the soils with unconventional behaviors. This paper explored the diatom inclusion effect on the artificial soils’ intrinsic compression behavior by oedometer tests and the microstructure evolution by SEM and MIP tests. This companion deposition process results in significant changes in both time-dependent consolidation and stress-dependent compression behaviors. The compression index and coefficient of secondary consolidation both increase with the diatom incorporation, but its swelling index remains almost unchanged. With the increase of compression stresses, the proportion of secondary consolidation in total deformation rises obviously. All mentioned prominent shifts in the compression behaviors are attributed to the alteration in the soil microstructure and water distribution caused by diatom participation. When slight diatoms are encapsulated in the clay matrix, their hollow structure increases the nominal clay porosity, but the soil still behaves as a pure clay and conforms to the classic ICL by Burland. Furthermore, with increasing diatom content, when the frustules in the diatom skeleton are broken and the accompanying clay minerals penetrate into the broken frustules, the creep deformation would be magnified unexpectedly. Therefore, a modified four-phase analysis framework of diatomaceous clays was introduced to unify their intrinsic compression behaviors, in which the diatoms and their affiliated ineffective water were isolated. It was found that the modified clay void index Ivc∗ parameter was effective to unify the soil’s compression behavior by excluding the isolated phases and to obtain the compression essence of diatomaceous sediments. This essence difference makes it improper to directly apply the concepts in traditional soil mechanics, such as the end of primary consolidation; moreover, it can be used to explain engineering disasters concealed in previous cognition.