| High-precision simulation of water seepage process in soil is of great significance to the fields of geotechnical engineering,hydraulic engineering and agricultural irrigation.Accurate determination of water diffusivity and permeability coefficient of unsaturated soil is the premise of high-precision simulation.In this paper,an approximate analytical solution of the one-dimensional horizontal imbibition Richards equation is established based on the idea of the constant variation method,combined with the horizontal imbibition method,an analytical-correction method for soil moisture diffusivity is established,which solves the problem that the determination of soil moisture diffusivity is easily affected by boundary effects from the algorithm.On the basis of analyzing the influence of boundary effect on horizontal imbibition and vertical infiltration,it is proposed to add a vertical buffer at the infiltration end of the horizontal imbibition soil column to solve the influence of boundary effect on horizontal imbibition,and combined with the rationality of the numerical test method,the problem that the soil moisture diffusivity is easily affected by the boundary effect is solved from the test method.Using the Philip series method to solve the Richards equation of one-dimensional vertical infiltration,according to the data of the water content of the monitoring point changing with time,determine the coefficients of each item of the series solution,using the first term coefficient,the water diffusivity of unsaturated soil is determined by the analytical-correction method,combined with the differential decomposition method of Richards equation,the calculation method of unsaturated permeability coefficient is further established,simultaneous calculation of water diffusivity and permeability coefficient in unsaturated soils using vertical infiltration.During this process,the following conclusions were drawn:（1）Under the first type of definite solution conditions,the solution of the one-dimensional horizontal imbibition Richards equation can use θ=θo－θinierfc［a（x/√Dt）b］+θini as the approximate analytical solution,through the Hydrus-1D numerical test,it is found that the determination coefficients of the approximate analytical solutions are all greater than 0.990,and for the same soil,a and b can be regarded as constants.The rationality of the analytical-correction method is verified by numerical experiments and laboratory experiments,the results show that the coefficients of determination of soil water diffusivity in the range of[θini,θ0]obtained by the analytical-correction method are all above 0.900,make up for the lack of horizontal imbibition method.（2）The infiltration of water in 0.75 m long horizontal and vertical columns was simulated by the Hydrus-1D software,the results show that,compared with the horizontal column,the water infiltration process of the vertical column is less affected by the boundary effect,inspired by this,consider adding a vertical buffer to the water outlet of the horizontal column,in order to reduce the problem that moisture is susceptible to boundary effects in finite-length soil columns,the results show that with the addition of a vertical buffer,the horizontal imbibition method is directly used to analyze the measurement point data,and the obtained soil moisture diffusivity has high accuracy in[θini,θ0],which solves the shortcomings of the conventional horizontal imbibition test.（3）When only the unsaturated permeability coefficient is considered,when the Philip series form should retain three terms,the accuracy of the calculation results of the five soils is high.At the same time,considering the calculation accuracy of unsaturated soil water diffusivity and permeability coefficient,for Sandy Loam and Sandy Clay Loam,2 terms should be retained in the Philip series form,3 terms should be retained for Loam,Silty Loam and Silt,in this case,the coefficients of determination of the calculated results of diffusivity and permeability coefficient are both greater than 0.9200. |
