Study On Soil Water Characteristic Curve Model And Prediction Of Collapsible Loess In Lanzhou

As an important soil hydrodynamic parameter,the soil water characteristic curve reflects the soil water-holding capacity and the distribution of soil pores.It is an indispensable part of interdisciplinary content such as soil hydrodynamics,unsaturated soil mechanics,and ecological hydrology.In view of this,this paper takes the soil in the 0～30 cm soil layer of Lanzhou collapsible loess as the research object.Through field sampling and laboratory experiments,the influence of different particle diameters,bulk density,and depth on the soil water characteristic curve were explored.Classical and geostatistics statistics methods are used to analyze the temporal and spatial variability of the soil water characteristic curve model parameters.In addition,low suction section and the inflection point are considered to make representative prediction of soil moisture characteristic curve.The main contents are as follows:(1)In order to find out the influence of different factors on soil water characteristic curve,the laboratory experiment was used to analyze the change law of soil water characteristic curve with different bulk density,particle size and depth,and to determine the suitability of soil water characteristic curve model.The results showed that the soil water content decreased with the increase of matric suction under different factors.Six models(VG-M(m,n)、VG-M(1-1/n,n)、BC-M、VG-B(m,n)、VG-B(1-2/n,n)and BC-B)were used to fit soil water characteristic curves with different bulk density,particle size and depth,and error analysis was conducted.The results showed that VG-M(1-1/n,n)model had the highest fitting accuracy.This result can provide a theoretical basis for the improvement design of soil collapse and erosion of collapsible loess in the study area.(2)The spatial variability of soil water characteristic curve model parameters of Lanzhou collapsible loess was analyzed by using classical statistical method and geostatistical method.The results show that:0～30cm soil water characteristic curve model parametersαbelong to medium variability,n,θ_s belong to weak variability,with the increase of soil depth,Cv gradually increases.In order to intuitively observe the spatial distribution of each parameter,this paper draws the trend surface analysis diagram and three-dimensional spatial distribution diagram,and finds that the spatial distribution of different model parameters are obviously dispersed,and the distribution is divided into three parts.The distribution pattern is consistent with the migration direction.The results can provide a scientific reference for the analysis and calculation of water movement law of collapsible loess in Lanzhou.(3)The time stability of VG-M(1-1/n,n)model parameters in 0～10cm soil layer in 2019 was comprehensively compared by using average relative deviation,standard deviation of average relative deviation and time stability index,and the representative measuring points 2,9,11,12,13 and 16 were determined.The VG-M(1-1/n,n)model parameter data verify the prediction accuracy of different representative measurement points.It is found that the determination coefficient between the predicted value and the measured value of each measurement point is large,and the standard deviation is small,but the prediction accuracy of point 16 is the highest.Therefore,No.16sampling point is selected as the representative point to predict the parameters of VG-M(1-1/n,n)model in this area.The results of this study are helpful to the reasonable planning of soil and the reasonable layout of monitoring points in this area.(4)The soil water characteristic curve was predicted by using low suction section and reverse bending point.The results showed that:using the symmetrical geometric characteristics of the"s"shaped soil water characteristic curve,taking 1.58g/cm~3 bulk density as an example,the soil water characteristic curves determined by comparing the measured data of different suction sections on the reverse bending points.It was found that the soil saturation of the soil water characteristic curve obtained from the data of 0～800 cm suction section was the highest,and the correlation coefficient was 0.9941.The average absolute error and root mean square error of soil water characteristic curve data with different texture and bulk density were close to 0,and the correlation coefficient and determination coefficient were close to 1.The results can be used as a simple method to predict soil water characteristic curve and provide theoretical guidance for soil water management in collapsible loess area.