Abstract: The deep-sea rare earth-rich sediments are exploited in the Pacific district. In this study, the conventional physical properties are studied by analysis of laser particle size, test of liquid and plastic limit, and mineral compositions and microstructures are analyzed by X-ray diffraction(XRD) and scanning electronic microscope(SEM) method respectively. Test result shows that the deep-sea rare earth-rich sediments have high liquid limit, high plasticity, and their mineral compositions is mainly composed of primary minerals such as quartz, calcite, halite, feldspar, mica, and secondary minerals such as green stone. The microstructure is mainly composed of links structure and honeycomb-like sheet structure. In addition, the routine geotechnical experimental method can’t test the strength of this kind of deep-sea rare-earth-rich soft sediments，the sediment rheological tests under different temperatures and water contents are conducted by the Brookfield's RST rheometer, and the relevance of the undrained shear strength, yield stress and apparent viscosity with moisture content and temperature are analyzed according to the experimental results. Then, the Herschel-Bulkley model is introduced to discuss the rheological parameters. Further, the rheological characteristics and mechanisms of the deep-sea rare earth-rich sediments are analyzed by the phase transformation and the interparticle interaction. The results show that water content and temperature have a significant effect on the shear stress and apparent viscosity of the sediment. Compared with normal temperature conditions, the shear stress and apparent viscosity of the sediment are significantly increased in a low temperature environment. The apparent viscosity and the yield stress decrease as the moisture content of the sediment increases. This result can provide a scientific basis for the fluidized transportation of deep-sea rare earth-rich sediments.

Key words: deep-sea rare earth-rich sediments, microstructure, viscosity, shear stress, shear rate