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Abstract To investigate the effects of different pore water environments on compressive behaviours of the deep-sea soft soil from South China Sea, four kinds of soil samples including natural sample with sea water or deionized water, remolded sample with sea water or deionized water were prepared, respectively. Then, a series of oedometer tests and scanning electron microscopy tests were performed on the above samples to examine their compressive behaviours and microscopic characteristics, respectively. Additionally, the microscopic pore distribution of natural sample with sea water was observed by mercury intrusion porosimetry tests. The effects of different water environments on macroscopic compressive behaviours and microscopic particle characteristics are analyzed. The deionized water environment increases the compressibility and decreases the consolidation coefficient for natural samples after structural breakage and remolding. The microscopic particle characteristics corresponding to the macroscopic compressibility are also qualitatively analyzed. In deionized water environment, soil particles exhibit higher roundness, more orderly and lower surface roughness than that in seawater environment. In this study, the deionized water environment has no obvious effect on the structural yield stress and secondary consolidation coefficients of deep-sea soft soil. [ABSTRACT FROM AUTHOR]

Chemical conditions have significant effects on the engineering properties and microscopic characteristics of the dredged fill. In this study, a series of laboratory tests were conducted to investigate the engineering properties and microscopic characteristics of the dredged fill under different chemical conditions. In addition, the micro-mechanism of the effect of chemical conditions on the engineering properties of the dredged fill is revealed. Under alkaline conditions, the undrained shear strength and structural yield stress increased by 50.33 and 145 kPa, respectively. The particle morphology was transformed from a granular and flaky structure to an agglomerated structure, and the surface-to-surface connection was the main form of intergranular connection. These changes reflect the enhancement of the intergranular cementation strength of the dredged fill by the generated insoluble substances and suggest that adding a certain amount of alkaline materials is an effective method to improve the engineering properties of dredged fill. Under acidic conditions, the undrained shear strength was significantly decreased, while the compressibility was notably increased. The cementation between soil particles was severely damaged due to the corrosion of hydrogen ions, leading to an increase in the number of large-diameter pores in the dredged fill and a deterioration of the microstructural characteristics. Under saline conditions, the undrained shear strength was reduced by 5 kPa, and the compressibility was increased. No distinct agglomerated structures were formed due to the dispersion of the internal particles of the dredged fill, and the soil skeleton effect was not notable. • The basic chemical elements and mineral composition of the dredged fill were determined by ICP-OES test and XRD test. • The relevance between chemical conditions and engineering properties was investigated by a series of laboratory tests. • The microscopic characteristics of dredged fill under different chemical conditions were investigated by MIP and SEM tests. • The bonding strength of cemented granules is enhanced due to the insoluble substances generated in alkaline condition. [ABSTRACT FROM AUTHOR]