Abstract: At present, the microstructure and compression characteristics of marine soft soils in onshore and shallow seas are widely studied, while those of deep-sea soft soils are less studied. However, with the development of marine engineering to deep water, the characteristics of deep-sea soft soils deserve attention. Diatomite is widely distributed in the deep sea and it is a kind of deep sea soft soil. It has diversity and does not follow the characteristics of classical soft soil laws. Currently, there are few studies on in-situ undisturbed samples. To investigate the microstructures, compression characteristics and secondary consolidation properties of deep-sea diatomite, scanning electron microscope (SEM) analysis, mercury intrusion porosimetry (MIP) tests, traditional oedometer tests and multistage oedometer tests (7-day loading for each stage) were carried out on diatomite sampled from the western Pacific Ocean at the depth between 4 423 and 4 674 meters. The experimental results show that the compression index of deep-sea diatomite ranges from 1.7 to 1.95, which is about 0.6 to 1.2 larger than that of other terrestrial and shallow marine soft soils. In addition, in the creep stage after consolidation, diatomite still has volume deformation for a long time, and there is no stable trend of deformation convergence, which may be caused by the continuous breaking of the shell of diatom particles. This hypothesis has been confirmed by SEM and MIP tests observation results in the loading stage.

Key words: deep-sea diatomite, microstructure, one-dimensional compression characteristics, creep characteristics；particle breakage, macro and micro combination