Study On Soil-water Characteristics Of Nanjing Sand With Respect To Macroscopic And Mesoscopic Scale

Nanjing sand is a kind of typical flake-shaped silty fine sand with different parameters on its grading,grain's shape,anisotropy,and mechanical properties comparing with the standard sand.The soil-water characteristics of Nanjing sand were studied in both the mesoscopic scale and the macroscopic scale.In mesoscopic scale,serial sectional images of a loose Nanjing sand sample were obtained at drying state(Water content is 0),excessive water state(Height of water level is over height of the sample,and water content is 40%),and two unsaturated states(Water content is 23%,and 27%)by using synchrotron radiation micro-computer tomography,then converted to binary images with image processing.By using pore network model,REVs'(Representative Elementary Volume)pore parameters(Included porosity,pore number,pore radius,throat radius,coordination number,etc.)were extracted from 5 heights of samples at different water content states.With the capillary fractal model and extracted REVs' pore parameters,REVs' permeability was finally calculated,which showed that Nanjing sand's permeability is 2.7415×10-6mm2 at dry state,the permeability is 13.4019×10-6mm2 at water-excessive state,the permeability is 27.3117×10-6mm2 at unsaturated state(Water content is 27%),and Nanjing sand's permeability is 23.6914×10-6mm2 at unsaturated state(Water content is 23%).In macroscopic scale,a filter-paper method was designed to measure matric suctions and the soil-water characteristic curve of Nanjing sand was generated.Finally,the connection between mesoscopic parameters and macroscopic parameters was studied with a comparison between mesoscopic results and macroscopic results.Conclusions were drawn:(1)With water content decreasing,the entrapped air leads to the formation of big pores and its development in Nanjing sand sample.(2)There are three pore sizes on Nanjing sand's pore at unsaturated state:the crack scale,the bubble scale and the pore scale(3)When mass water content of Nanjing sand changed from 27%to 23%,permeability,pore number,and maximum coordination number decreased,but matric suction,porosity,maximum pore radius and maximum throat radius increased.Inside these,matric suction changed most.