黄土水分场光纤原位监测及非饱和渗透系数估算

土壤含水率和渗透系数的原位测定是研究黄土高原地区各类地质灾害机理的重点和难点。应用基于AHFO的含水率测量方法,对降雨条件下黄土地基的水分场动态分布进行原位监测;以含水率监测结果和土水特征曲线为基础改进传统瞬态剖面法,估算蒸发条件下黄土的非饱和渗透系数。结果表明:①土壤中的水分运移受重力、吸力梯度和大气蒸发力的综合控制;降雨后黄土中的水分循环主要发生在浅层,降雨量较大时,土壤剖面呈现出干湿交替的现象;降雨量较小时,水分入渗到一定深度即向上部运移排泄;②改进的瞬态剖面法可以避免含水率分布函数和吸力未知所带来的计算误差,实现蒸发作用下黄土的非饱和渗透系数估算;③非饱和渗透系数计算值与平均含水率成正相关关系,但离散性较大,其误差主要来源于土壤性质的空间变异性和蒸发作用的滞后性;④该研究成果为降雨入渗模型的建立提供了精确的含水率和渗透系数,可广泛应用于黄土高原地区的原位试验研究。

In-situ Monitoring of Moisture Field and Estimation of UnsaturatedPermeability Coefficient of Loess Foundation

The field determination of soil moisture and permeability parameters is a key and difficult problem in analyzing various geohazards in loess regions. Using the Actively Heated Fiber Optics (AHFO)-based soil moisture measuring method, the dynamic distribution of moisture field in a loess foundation was captured in the field under rainfall infiltration condition. Based on the in-situ measurements of water content and the soil-water characteristic curve, the traditional transient profile method is improved to estimate the unsaturated permeability coefficient considering the evaporation effect. The results show that the process of soil water evaporation and redistribution is controlled by gravity, suction gradient and atmospheric evaporation force. The water cycle in the loess area mainly occurs in the shallow soil layer. When there is a large amount of precipitation, alternation of drying and wetting in the soil profile occurs. When the rainfall is small, the water penetrates to a certain depth and then migrates upward. Using tThe improved transient profile method, can calculate the unsaturated permeability coefficient under the evaporation condition can be calculated, and effectively avoid the calculation errors caused by unknown moisture content distribution function and suction are effectively avoided. The calculated unsaturated permeability coefficient is positively correlated with the average water content, but it is highly scattereddiscrete. The errors mainly comes from the spatial variability of soil properties and the lag of evaporation. The proposed methodresults provides accurate water content and unsaturated permeability coefficient for the analysis of rainfall infiltration model and can be widely used in in-situ test studiesy.