The Mico-quantitative Study Of Structural Of Net-like Red Soil In Xuancheng

There are differences between undisturbed soil and remolded soil of net-like red soil in macro-mechanical properties which are determined by their microstructure.In order to reveal the differences further,the microstructure of undisturbed soil and remolded soil is compared and analyzed quantitatively based on indoor impaction test and SEM-EDS and digital image processing technology.The influence of different magnifications and different thresholds selection on the calculation of the three-dimensional porosity in the effective threshold interval is analyzed.Moreover,the relationship between the average contact area rate and macro-porosity is investigated.The main conclusions are drawn as follows:(1)Based on the digital image processing technology and the results of SEM tests of remolded net-like red soil,the three-dimensional porosity calculation model in effective threshold interval is built up according to the pixel area as the bottom surface and the threshold as the height range.The pore numbers and area parameters of SEM images are analyzed under various experimental conditions,which indicate that the three-dimensional calculation method is more reasonable and reliable through comparison with that obtained by the plane calculation method.(2)The quantitative analysis results of the micro-porosity of remolded net-like red soil show that the three-dimensional porosity is mostly larger than the macro-porosity,and the results which are got at the magnification of 2000 times are closer to the macro-porosity.The selection of threshold is the key step in the process of quantitative analysis.The three-dimensional porosity of average threshold is much smaller than that of final threshold.The analysis of average contact area rate indicates that average contact area rate of samples is below 3%,and the relationship of power function between the average contact area rate and macro-porosity is obtained with the characteristics of the hydrated film thickness of 300?.(3)The results of micro qualitative analysis on undisturbed net-like red soil indicate that soil particles in the red matrix are closely arranged and the porosity is small.Furthermore,the connectivity between the pores is poor and the surface of the soil particles is rough.The porosity and the number of pores are larger in the white vein,and most of the soil particles are smooth sheet structure and mainly in the form of surface-surface contact.The results of quantitative analysis show that the average value of calculation of three-dimensional porosity of the red matrix is 0.371,while the average of calculation of three-dimensional porosity of the white vein is 0.450.(4)The results of EDS tests indicate that the main chemical elements of the red matrix and the white vein are oxygen,silicon,aluminum and carbon,and a small amount of potassium and magnesium.The loss of iron is the main reason for the color difference between the white vein and the red matrix,and there is enrichment phenomenon of iron element.The carbon element provides evidence for the view of the migration of iron elements due to the formation of acidic reducing environment because of organic acid of n et-like red soil.