Research On Migration And Distribution Of Capillary Water In Soil Based On AHFO

Capillary water is an important part of water field in unsaturated soil.Its seepage and distribution have an important influence on the microstructure,mechanical properties and engineering properties of soil.Therefore,it is an important research topic in engineering geotechnical and soil science to study the maximum rising height,rising rate,rising water and its influence on soil strength,and to make quantitative analysis through the model.The water field active heating optical fiber method(AHFO)has the advantages of long-distance and distributed in-situ monitoring,and has been used more and more in the monitoring of unsaturated soil water field.This paper uses this method,combined with Green-Ampt model,Terzaghi model and Lucas Washburn model,to monitor and evaluate the seepage and distribution of capillary water in unsaturated soil.The related research work and results are summarized as follows:(1)This paper reviews the research process and development status of capillary water seepage and distribution law,summarizes the current conventional soil moisture measurement methods and their advantages and disadvantages,and focuses on the monitoring principle and technical advantages of AHFO method.(2)Based on the dynamic analysis and movement characteristics of soil moisture,the Richards model for describing the hydraulic law of seepage process is derived,and the young Laplace equation for describing capillary flow is obtained.On this basis,based on different assumptions,the green amp model,Terzaghi model and Lucas Washburn model for describing capillary water seepage in soil are obtained and compared The hypotheses and theoretical characteristics of different models are given.(3)The capillary water seepage test in layered soil was carried out.The capillary water rising rule and the characteristics of each stage were analyzed by combining the capillary water rising rule prediction model(Terzaghi model,green Ampt model)and the maximum capillary water rising height prediction model(lane model,peck model).The whole process of capillary water rising is divided into two stages: 50 hours ago and 50 hours later.Due to the different errors of model assumptions in different stages,there are also differences in the size and accuracy between the predicted value and the measured value in the two stages.Therefore,the analysis idea that Terzaghi model is used in the former stage and green Ampt model is used in the latter stage to improve the prediction accuracy is proposed.The analysis results show that the peak model is more accurate than the lane model in predicting the maximum rise height of capillary water,and its form is simple,and its parameters are easy to obtain.It is suggested to use the peak model in engineering practice.(4)On the basis of experiments,the law of capillary water infiltration rate and rising height in homogeneous soil is obtained.The saturated permeability coefficient and matrix suction at the wetted front are obtained by green Ampt model inversion,and the conclusion that the permeability coefficient of unsaturated soil is less than that of saturated soil is verified by theoretical analysis.(5)Based on the results of AHFO test of moisture content distribution of homogeneous soil and layered soil,combined with Lucas Washburn model,the seepage law and distribution characteristics of capillary water in the rising process are analyzed.The phenomenon of capillary barrier in the rising process of capillary water in layered soil with different soil layers is found,and the movement rate and moisture content of capillary water in different soil layers are analyzed Based on the analysis of mechanism,it is considered that these phenomena and differences are caused by the discontinuous changes of matrix suction,hydraulic conductivity and particle viscosity resistance in layered soil,and an improved Lucas Washburn model is proposed to describe the seepage law of layered soil.(6)In the loess area of Ganguyi Town,Yan'an,the longitudinal test pit and the lateral watershed water monitoring were carried out,and the seepage law and the influencing factors of the water field in the loess area were analyzed.The results of soil analysis and monitoring in the vertical test pit show that the composition of soil particles will affect the capillary water seepage and final distribution.The more silt particles and the less sand particles,the higher the water content in the soil.When clay particles exist,the matrix suction will increase,and the water content in the soil will increase.According to the monitoring results of the transverse drainage basin,for the slope,the water content decreases slowly from the bottom to the top of the slope.The volume water content of the soil in the depth of 50 cm is greater than that in the depth of 10 cm,but the mass water content of the soil in the depth of 10 cm is greater than that in the depth of 50 cm because the dry density of the lower layer is greater than that in the upper layer.At the same time,the applicability of green Ampt model in Loess seepage is verified by simulating rainfall infiltration process in field.