NMR-Based Study on Pore Water Form and Permeability of Soil
In order to explore the effects of hydraulic gradient and pore water form on soil permeability,the NMR T2 curves of disturbed soil are measured under 8 kinds of suction such as 0-500 kPa.The pore water is divided into movable water and immobile water,the relationship between movable water and suction/hydraulic gradient is quantitatively analyzed,and the hydraulic gradient and movable water are introduced into Coates permeability model to be corrected.The result shows that (1) the T2 curve area of soilmass and the maximum value of T2 gradually decrease as the suction increases from 0 kPa to 500 kPa ( the hydraulic gradient increases from 0 to 50),and the minimum value of T2 is almost unchanged;(2) with the increase of suction/hydraulic gradient,the movable water first increases rapidly,then increases slowly,and tends to be stable finally;(3) these two can be well fitted with an exponential function,and the immobile water content decreases exponentially with the increase of suction/hydraulic gradient;(4) the ratio of movable water to immovable water (FFI/BVI) and hydraulic gradient is fitted with a linear function;(5) the simplified Coates model shows that the permeability of soil is directly proportional to the quadratic hydraulic gradient;(6) pore radius is the key factor affecting seepage of soil,under the influence of suction/hydraulic gradient,the process of water drainage can be described with Young-Laplace equation,the pore water starts to drain from macropores and gradually develops to micro-pores,and the macro-pores complete the drainage process firstly;(7) the increase of hydraulic gradient raises the proportion of movable water,leading to more movable water participating in seepage and a significantly increase of soil permeability.The simplified Coates model visually shows the relationship among hydraulic gradient,pore water form and permeability,containing only an unknown ( hydraulic gradient ),and providing a theoretical reference for subgrade stability analysis and protection design.
road engineeringpermeability modelnuclear magnetic resonancehydraulic gradientpore water form
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