Study on soil shrinkage characteristics during soil water characteristic curve measurement

Clay loam soil from Yunnan(KM),sandy loam soil from Liaoning(SY) and Xinjiang(KL),and loam soil from Shandong(LY) were selected for analyzing the characteristics of soil shrinkage duringsoil water characteristic curve measurement in order to explore the suitability of fitting models for soil watercharacteristic curve,and the changes of soil shrinkage. In this paper,soil water characteristic curves ofthe four soil types were measured by centrifuge method and were fitted by RETC software. The resultsshowed that as for KM,SY,KL and LY soils,firstly,soil moisture content gradually decreased with soilsuction increasing from 0 to 7000 cm. And the rate of soil water reduction decreased,and then increased,and then decreased again. Secondly,all fitting models presented in RETC software were of high accuracyfor the simulation of soil water characteristic curves,and the appropriate fitting models for KM,SY,KLand LY soils were VG-M(m,n),LND-M,VG-M(1-1/n,n) and VG-B(m,n),respectively. And VGmodel could be considered as the optimal model for simulation of soil water characteristic curves of thefour soils. Thirdly,a logarithmic function was found between degree of effective soil shrinkage and soil suc-tion during soil water characteristic curve measurement. The soil shrinkage was ranked in the order of SY KM LY KL,and the bulk density of the four soils increased by 0.19 ~ 0.46 g/cm3. Fourthly,soil shrink-age process could be roughly divided into pseudo-saturated stage,structural stage and super-normal stage.And as for KM,SY,KL and LY soils,the three stages could be described by linear function,but theranges of soil suction corresponding to three soil shrinkage stages were different.