| In view of the characteristics of low rainfall and large evaporation in arid and semi-arid regions of China.This paper analyzes and summarizes the research status of domestic and foreign water-saving irrigation technologies,proposes a new water-saving irrigation technology,and designs a gravity-type underground hole irrigation system with the dual functions of “collecting rain” and “irrigation”.Through the combination of laboratory test and numerical simulation,a model of soil water movement under the condition of gravity-type underground hole irrigation was established,the law of soil water movement was analyzed,and a simplified model of infiltration factors was established.The characteristics of soil infiltration and the law of water movement under the condition of gravity-type underground hole irrigation were studied,and the following research results were obtained:(1)A gravity-type underground hole irrigation system with the dual functions of rain collection and irrigation was designed,and the test scheme is designed and an laboratory test was conducted.The soil water movement law under different pressure head,vertical pipe diameter and depth was studied through laboratory soil box test.(2)The unsaturated soil water diffusivity is one of the essential parameters for studying the law of soil water movement.The soil water characteristic curve was measured by a high-speed centrifuge method,and the water diffusivity of unsaturated soils was measured by a horizontal column suction method.After fitting the measurement data of the two,the relevant values of the van Genuchten(VG)model were obtained.(3)Based on the soil moisture dynamics equations,the soil water movement model and boundary conditions for gravity-type underground irrigation were established.The model was used to simulate the cumulative infiltration volume,the moisture distribution of the wetted body and the distance of the wet front in the gravity-type underground hole irrigation.The simulated and measured values were compared and analyzed.The results showed that the simulated value was in good agreement with the experimental value.It shows that the proposed model and algorithm can be applied to the cumulative infiltration of soil,the distribution characteristics of wetted body and the rule of the distance of wet front migration under the conditions of gravity-type underground hole irrigation.(4)The method of numerical simulation was used to simulate the laws of cumulative infiltration,wet soil moisture distribution,and wetting front migration distance under the combination of different irrigation technology elements.Under the condition of the same soil moisture infiltration time,the pressure head and pore diameter have a significant effect on the cumulative infiltration,and the depth of the vertical pipe has little effect on it.The pressure head and pore size have a greater influence on the distribution of soil moisture.The greater the pressure head and pore size,the more obvious the wetted area and the higher the moisture content at the same cross section,the depth of the vertical pipe has little effect on the distribution of soil moisture,and the moisture content at the same section is not much different.The change law of wetting front: At the initial stage of infiltration,due to the effect of the matrix potential,the rate of advancement of the wet front is relatively large,but with the prolongation of the irrigation time,the advance rate of the wet front gradually decreases,tends to a gentle stage,and finally achieves a relatively stable infiltration state.The distance of the wet front presents a vertical downward greater than the horizontal Direction,horizontal direction is greater than vertical upwards.Therefore,in the design of gravity-type underground hole irrigation engineering,the impact of different pressure heads and apertures on irrigation needs to be considered,but its depth should be determined according to actual conditions.(5)A simplified infiltration model under different irrigation technology combinations was established and verified that the simplified model established was reasonable.The Philip model is used to characterize the relationship between the cumulative infiltration amount and the infiltration time of the gravity-type underground hole irrigation,and the power function is used to characterize the change of the migration distance of the wetting front. |
