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An approach to detecting the characteristics of different pore fluids in soils based on the NMR technique

Identification of the type, content and characteristics of pore fluids in geomaterials is important in polluted soil remediation and fossil fuel exploration, and also plays a crucial role in analyzing the chemo-mechanical behavior of geomaterials. Here the nuclear magnetic resonance (NMR) technique is introduced to explore the characteristics and distributions of pore fluid mixtures, which are composed of distilled water, gasoline and/or diesel oil in the fine grained soils. A NMR-based method is then proposed to identify the type and content of pore fluids in the soils in a direct and non-destructive way. We show that 1) the relaxation time T2 and the NMR signal peak value of pore water decrease as the dry density of the tested soil increases; 2) compared to the relaxation time T2 of a fluid (distilled water, gasoline or diesel oil) at its free state (outside the pores), the T2 is significantly reduced when the fluid is located in the pores, implying that significant physicochemical interaction exists between the fluid and the soil matrix; 3) at the same dry density, the relaxation time T2 of pore diesel oil is larger than that of pore gasoline, and the T2 of pore water is smallest; 4) there exist two peaks in the T2 distribution curve of the soil saturated with two or three fluids. The double-peaks phenomenon in the soils saturated with water and diesel oil is the most striking, compared to the soils saturated with other fluid mixtures. However, the amplitude of NMR signal in the T2 distribution curve of the soil saturated with gasoline and diesel oil is reduced most significantly, while the range of the relaxation time T2 remains unchanged; 5) the content of different fluids in the mixture pore fluids of the soils can be measured.

Author(s):

Pan Chen    
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
China

Changfu Wei    
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
China

Huihui Tian    
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
China