线源入渗仪布水器水力特性的理论分析与试验

布水器是土壤入渗线源测量方法的重要组成部分。该研究提出了一种线源布水器的新型材料与结构。布水器采用特殊的海绵材料制作。从理论上对理想布水器的材料要求进行了深入地分析。在此基础上,选用合适的海绵材料进行试验以确定布水带材料。采用离心机测量了所选用的海绵材料-103~-105 Pa范围内的水分特征曲线。这种材料中的含水量与水吸力之间具有很好的幂指数关系,相关性系数R2=0.948,在低水势时,含水量维持在很低的水平,当水势增加时含水量几乎维持不变。当水势超过一定值后,含水量随着水势的增加急剧增加。用水势连续的概念,分析了水在布水器和土壤界面运动的特征,说明试验中所选用的海绵在水力特征上是理想的布水器材料。给出了布水器的结构。用制作的布水器进行室内试验,地表湿润面积推进过程具有非常好的线性,验证了对布水带水力特性的分析以及试验得到的材料水动力学数据,说明了线源布水器的可行性。该研究将有助于土壤入渗线源测量方法的实际应用,也为相关的研究提供借鉴。

Theoretical analysis and experiment of hydrodynamics of water distributor for linear run-on infiltrometers

Abstract: The water distributor is one of the important components of the linear source method for soil infiltability measurement. This study suggested a new material and structure of the water distributor, which used special sponges to make the key component for water distribution. The water distributor was composed of a water supply tubing, a water distribution chamber, a level, a sponge strip and a fixing plate. Theoretical analysis was made to detail the requirements of an ideal water distributor for even distribution of water flow supplied to soil surface for infiltration along its length. Hydrodynamics of water movement inside the water distribution sponge along its length and those at the interface both inside the soil and the water distribution sponge were analyzed. Analysis was made on the conditions for identifying the materials for the water distributor manufacturing. Trials were made to select the sponge materials of ideal hydraulic responses before water distributors were made and used in the experiments to identify their hydrodynamic responses. A centrifuge machine was used to measure the pF-curves of the sponges, ranging from -105 Pa up to -103 Pa. The exponential function was used to fit the measured data between the water content and suction. For the ideal material chosen from the experiments, there was a good relationship between the water content and soil-water suction, with the coefficient of determination, R2=0.948. Water content remained very low and almost constant as the water potential inside the sponge increased at its low level (i.e. large negative values). After some critical value of the water potential, the water content increased very rapidly with an increase in water potential. Water potential continuity concept was used to analyze the water movement in the interface between soil surface and the water distributor. The results indicated that the sponge selected for the experiment was an ideal hydrological material for the water distributor. The details of the water distributor structures were also obtained from the study. Manufactured linear water distributors were used for actual water application under laboratory condition and the wetted area on soil surface had a very good linear pattern. The measured results verified the hydraulic characteristics analysis of water distributor and hydrodynamic data through the experiment demonstrating the feasibilities of the newly suggested linear water distributor. This study will help the application of the linear run-on method for soil infiltrability measurement and relevant to some related applications.