Study Of Loess Pipe Flow Experiment And Its Infiltration Model

Loess is widely distributed in in northern China,and it is a kind of structural soil with tubular preferential channels.The distribution characteristics of the tubular preferential channels affect the seepage characteristics of the loess.During the rainfall,the tubular preferential channel promotes the rapid movement of water to the deep soil.It changes the water content and matrix suction of the deep soil,reduces the shear strength,and then induces geological disasters such as loess landslide.Therefore,it is of great theoretical and practical significance to study the influence of the tubular preferential channel on the seepage and water distribution of the loess.It can provide a reference for the mechanism and prevention of the loess landslide.First,this paper analyzes the causes of loess preferential channel,extracts the characteristic data of loess tubular channel by Image J,and analyzes its radius distribution characteristics.Then,we carry out the soil column infiltration test of loess tubular preferential channel,monitor the moisture data by volume water content sensor and matrix suction sensor,and record the infiltration volume and wet front position.The nuclear magnetic resonance analysis system and the seepage device are used to conduct the seepage test of the remodeled and original loess,and the distribution characteristics of water in the micropores of the loess samples with tubular preferential channels were analyzed.Finally,based on fractal derivative theory,an improved model of loess pipe flow is established and the model effect is evaluated.The full paper concludes the following conclusions:（1）Abiotic factors are conducive to the formation of planar fissure channels.Biological factors are conducive to the production of tubular channels.The equivalent radius of the loess tubular channels at the sampling point follows Weibull distribution.（2）The laboratory experiment of soil column infiltration shows that when the loess tubular channel area is unsaturated,the infiltration rate is significantly greater than the homogenous soil column infiltration rate.When the area of the loess tubular channel area is saturated,the infiltration rate of the soil column with the tubular channel is similar to that of the homogeneous soil column.The soil column with the tubular channel forms two moist surfaces due to the preferential infiltration.（3）The nuclear magnetic resonance permeation test shows that each T₂ relaxation spectrum of the remodeled sample and the undisturbed sample contains 2 peaks and 3peaks,respectively.With increasing time,T₂ relaxation spectra morphologically of the original sample and remodeled sample shifted to the right.The minimum pore size of the remodeled moisture increases with time.The larger the diameter of the tubular channel,the greater the height of the water head,and the smaller the minimum pore size of the remodeled sample moisture.The minimum pore size of moisture in the undisturbed sample is smaller than the minimum pore size of moisture in the remodeled sample.（4）Based on Hausdorff fractal derivative theory,Richards infiltration model and Green-Ampt model of fractal derivative are improved.The infiltration characteristics of tubular preferential channel are characterized by the order of fractal derivative.According to the cumulative infiltration curve,the fractal derivative orders of the T1,T2,T3,and T4 groups were 1,1.083,1.178,and 1.2073,respectively.The improved model agrees with the experimental results.