多因素影响下竖管地下灌溉入渗特性分析

为了研究压力水头、竖管直径、土壤初始含水率、土壤容重和入渗时间等5个因素对竖管地下灌溉入渗特性的影响。采用正交试验设计共安排了10组试验（9组试验，1组验证试验），利用竖管地下灌溉室内试验装置测定7 h内累积入渗量，构建累积入渗量与5个因素之间的量化关系式，量化关系式相关系数为0.98，决定系数大于0.99，表明该式可客观反映各因素与累积入渗量之间的关系。累积入渗量与压力水头、竖管直径和入渗时间呈显著性正相关，与土壤初始含水率和容重呈负相关。根据这一量化关系式得到入渗流量的表达式，入渗流量开始较大，为1.93～5.92 L/h，逐渐减小，经过5～6 h后趋于稳定，稳定入渗流量为0.08～0.25 L/h；用敏感性分析和相关系数分析各因素对入渗流量的影响，结果表明：压力水头是影响流量的主要因素，其次为竖管直径、容重和初始含水率；入渗流量与压力水头和竖管直径呈极显著性正相关，与土壤初始含水率、土壤容重和入渗时间呈负相关。这一结果对进一步研究竖管地下灌溉管网系统水力特性和技术要素具有重要意义。

Infiltration characteristics of vertical tube subirrigation as affected by various factors

Abstract: Subsurface irrigation is a type of water-saving technology. However, poor anti-clogging abilities and large energy consuming of the existing subsurface irrigation emitters present a significant obstacle to the development of subsurface irrigation. Aimed to this problem, a new type of subsurface irrigation emitter, vertical tube emitter, was proposed. This study investigated the effects of pressure head, vertical tube diameter, initial moisture content, and soil bulk density and infiltration time on infiltration characteristics of soil moisture under irrigation system with vertical tube emitter. Laboratory experiments were carried out in State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area in silt loam. The experiment was conducted using an orthogonal design method including 9 treatments and one control test. In the experiment, the pressure head was designed with different levels of 0.6, 1.3 and 2.0 m, the vertical tube diameter was 4, 8 and 12 mm, initial moisture content was 7%, 10% and 13% and soil bulk density was 1.32, 1.37 and 1.42 g/cm3. During the experiment, the cumulative infiltration was measured by difference of water levels in Markov bottle. The water level was recorded every 1, 2, 5, and 10 min in the first 100 min, every 20 min from 100 to 180 min, and every 30 min from 180 to 300 min, and every 60 min from 300 to 420 min. The empirical equation was established between cumulative infiltration and influence factors. The first derivative of the equation with respect to time was considered as the infiltration rate empirical equation. Then the partial deviation of the equation with respect to each factor could reflect sensitivity of infiltration rate to each factor. Based on the curves of influence factors and cumulative infiltration, an empirical model was established to estimate cumulative infiltration. The model had the determination coefficient of 0.96 and the measured and estimated values were correlated with correlation coefficient 0.98 (P<0.01). The model was validated with measured values of control test. The validation revealed R2 higher than 0.99 and the root mean square error from 0.1125 to 0.1353 L, indicating that the established model was good at cumulative infiltration estimation under irrigation system with vertical tube emitter. The effect of pressure head, vertical tube diameter and infiltration time on cumulative infiltration was the largest among all the factors. The infiltration rate decreased greatly during the first 2 h of experiment then stabilized after 5-6 h. The stable infiltration rate was 0.08-0.25 L/h when the pressure head was 0.6-2.0 m, vertical tube diameter was 4-12 mm, initial moisture content was 7%-13 % and soil bulk density was 1.32-1.42 g/cm3 during 7 h. The sensitivity analysis results showed that pressure head was the main factor affecting the infiltration rate, followed by vertical tube diameter, soil bulk density and initial soil moisture content. The infiltration rate had a positive correlation with pressure head and vertical tube diameter, however, had a negative correlation with initial moisture content and soil bulk density. And the rate of change of infiltration rate reduced gradually for all the influence factors. In the future, depth of vertical tube emitter and muddy water infiltration should be considered in studying the infiltration characteristics of soil moisture in the irrigation system with vertical tube emitter, and filed experiments should be combined with pipe network system to study the practical application effects of vertical tube emitter.