Study On Effect And Mechanism Of Drainage And Salt Removal Of Bottomless Airfoil Wall-Less Pipe

Object: In the arid areas of Xinjiang,water saving and saline-alkali land treatment are two fundamental problems to be solved in the development of local agriculture.The promotion of drip irrigation technology in a large area has laid a good foundation for the improvement of agricultural output and ecological protection in Xinjiang.However,drip irrigation technology is characterized by "shallow irrigation and frequent irrigation".The soil is always in an unsaturated state,which is not suitable for leaching soil salt into groundwater,which often leads to the accumulation of salt below the tillage layer.If the salt is to be washed out of the farmland,it needs to be specially irrigated with large amount of salt in the non-growth period of crops,and the salt is drained out by the hidden drainage pipe.However,the utilization of large amount of irrigation with salt is not conducive to the sustainable development of agriculture in Xinjiang.In order to realize the drainage and salt drainage of the hidden pipe under drip irrigation,the working situation of the hidden pipe with different cross section structure in unsaturated soil was studied to solve the dilemma of large amount of irrigation water needed to realize the drainage and salt drainage of the hidden pipe in drip irrigation farmland.Methods: In this thesis,based on the analysis of intercepting ability of different hidden pipe cross section structures,through carrying out soil column(one-dimensional condition)and soil trough(two-dimensional condition)test,drip irrigation and drainage of several hidden pipes with different cross section structures were studied.Among them,T1 is the round dark tube with impermeable bottom,T2 is the equilateral triangular dark tube with impermeable bottom,T3 is the round dark tube with impermeable bottom,T4 is the equilateral triangular dark tube with impermeable bottom.In addition,the drainage process under one-dimensional test condition is simulated so as to clarify the influence of the cross-section structure of the drainage tube on soil water flow in unsaturated soil and realize the drainage effect in unsaturated soil.Results:(1)The water trapping and holding capacity of equilateral triangular section is greater than that of circular section,and the area and width of equilateral triangular section are two times and 1.05 times of the latter.In the one-dimensional test,the soil moisture content of T2 treatment was 0.16% higher than that of T1 treatment at the top of the hidden tube.The infiltration velocity on both sides of equilateral triangular section is smaller than that of circular section,and the infiltration velocity of T2 and T4 at the furthest distance from the tube is 0.05 cm/h smaller than that of T1 and T3.Therefore,the equilateral triangular section of the hidden pipe is better than the circular section of the same performance of soil water flow around the phenomenon.(2)The suppression of soil water flow around the bottom of the hidden tube with wings was enhanced,and the water flow around the bottom of the hidden tube was less.In the one-dimensional test,at the bottom of the hidden tube,the average soil moisture content of T3 and T4 treatments was 0.64% and 0.51%lower than that of T1 and T2,respectively.In addition,the bottom wing concealed pipe also improved its capacity of drainage and salt discharge in unsaturated soil.Compared with T1 and T2,the displacement of T3 and T4 concealed pipe increased by 119.8 m L and 119.7 m L,respectively,and the salt discharge increased by 16.76 g and 18.83 g,respectively.The flow velocity around the bottom concealed tube with wings was lower than that of the same index without wings,and the infiltration velocity of T3 and T4 at the furthest distance from the concealed tube was 0.06 cm/h smaller than that of T1 and T2.(3)The drainage time of equilateral triangular section is earlier than that of circular section;The starting drainage time of T2 and T4 was 7.45 h and 1.13 h earlier than that of T1 and T3,respectively.The drainage time of the concealed pipe with bottom wing is earlier than that of the concealed pipe without bottom wing.The drainage time of T3 and T4 was 9.79 h and 3.47 h earlier than that of T1 and T2,respectively.(4)Under two-dimensional condition,soil moisture and salt were both higher at a longer horizontal distance from the bottom airfoil concealed tube than those above the concealed tube.The average soil mass moisture content of the left and right sections of the concealed tube treated by T3 and T4 was 0.02% and0.15% lower than that of the section with the furthest horizontal distance from the concealed tube,respectively.The average soil salt content of the left and right sections of the concealed tube treated by T3 and T4 was 0.02% and 0.12% lower than that of the section with the furthest horizontal distance from the concealed tube,respectively.Under two-dimensional condition,soil salt began to accumulate in the soil layer 10 cm below the hidden tube.Conclusion: In unsaturated soil,the effect of triangular section tube on inhibiting soil water flow was better than that of circular section tube.When the bottom wing is added to the hidden tube,its inhibition to flow around can be further improved,and its capacity of drainage and salt removal can be improved.In unsaturated soil,the area of drainage and salt drainage of hidden pipe is small,so it is necessary to increase the density of hidden pipe to achieve large area of drainage and salt drainage.