Study On Soil-water Characteristic Curve And Pore Characteristics Of Compacted Loess

The foundations of the loess embankment,dam foundation,and the land creation are all constructed by unsaturated compacted loess.The soil-water characteristic curve is a key constitutive relationship for the study of unsaturated soils.To have a better understand of the unsaturated properties of compacted loess,This paper takes Heifangtai Loess in Gansu as the research object,selecting three compaction water content(dry of optimum,optimum,and wet of optimum)and their corresponding dry density to make remolding soil samples by compaction.Carrying on mercury intrusion porosimetry and scanning electron microscopy test for intact and compcted loess,and testing the soil-water characteristic curve of the compacted loess by filter paper method,through comparing and analyzing their soil-water characteristic curve and pore characters,have achieved the following results:(1)Obtained the pore distribution curve of intact and compacted loess,divided the the pore distribution curve in to macroscopic pores and microscopic pores with 0.2?m.For the specimen compacted at dry of optimum,the PSD curves have peak points both in the macro and micro pores,which is approximately to the intact loess,and thus its soil-water characteristic curve justified the bimodal mode;However,there is only peak points in the macroscopic range at the PSD curves of loess compacted at optimum and wet of optimum.Analyzing and comparing pore distribution curve of intact and compacted loess,the results show it's the macroscopic pores that compaction mainly change,and it doesn't have notable influence on the microscopic pores.(2)According to the results of scanning electron microscopy,the pores in the specimens compacted at dry of optimum and optimum is more connected,but there is a certain number of sealed pores in the specimen compacted at wet of optimum.(3)The results of SWCC measurements of compacted loess were fitted by Gardner,van Genuchten and Fredlund & Xing SWCC equations,and the result shows that the Fredlund & Xing fit best.The datas of SWCC of loess compacted at dry of optimum was superimposed fitted by the equation of Fredlund & xing,the fitting results are closer to the test value than the overall fitting.The SWCC for loess compacted at different initial water intersect at one point,where the water content is close to the optimum water content determined by the compaction curve.(4)The differences in the soil-water characteristic curves of the three compacted loess were explained using the pore distribution curves and microstructure images,and the reasons causing the hysteresis of the soil-water characteristic curves of the three compacted loess were analyzed.(5)From analysis it is known that the mercury intrusion process is similar to the soil water drying process,therefore,through taking different contact angle,a method for calculating drying and wetting SWCC based on pore size distribution is proposed.