Calculation method of drainage flow in field subsurface pipe based on image method
In view of the fact that there is no suitable method to calculate the drainage flow of con-cealed subsurface pipes that takes into account the influence of composite envelope materials at present,this paper combines the image method and the superposition principle of potential flow in seepage mechanics.A formula for calculating the drainage flow rate of concealed pipes considering the influence of outsourced filter materials was proposed under the background of winter irrigation and salt washing in Yinbei Irrigation District,Ningxia.The relevant hydraulic characteristic parameters were determined through indoor seepage tank tests and HYDRUS-2D software simulation.The experimental data,numerical simulation,and Numerov solution were compared and analyzed with the calculation formula in this paper.The results show that the relative errors between the formula calculated values and the seepage tank test data and numerical simulation values are within 7.00％and 2.05％respec-tively.When the thickness of the envelope material is less than 15 cm,the formulas in this article and the Numerov solution introducing the concept of effective radius both have a high degree of agreement with the simulated values.When the thickness of the envelope material is greater than 15 cm,the for-mula in this paper is closer to the numerical simulation value and better than the Numerov solution.The drainage flow rate of subsurface pipe gradually increases with the increase of the permeability coefficient or thickness of envelope material,but the growth rate gradually slows down.The formula for calculating the drainage flow rate of subsurface pipe composed of composite envelope materials based on the image method is reasonable and feasible,expanding the calculation concept of subsurface pipe drainage.
subsurface pipe flowenvelope materialimage methodpotential energy superposition
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