土体水分蒸发研究进展

Advances on soil moisture evaporation

土体水分蒸发是土体-大气物质和能量交换的主要过程之一,对土体的工程性质有重要影响,是许多工程和环境问题的直接诱因,但长期被本学科所忽视。基于国内外近些年来其他学科领域围绕土体水分蒸发问题所取得的研究成果,分别从土体蒸发量确定方法、试验方法、蒸发过程、影响因素及理论模型等几个重要方面总结了该课题的研究现状及进展,取得如下主要认识:(1)准确确定土体的实际蒸发量是土体水分蒸发研究的核心课题,目前主要有理论计算法和直接测量法两种途径;(2)开展蒸发试验是掌握土体水分蒸发过程和研究土体水分蒸发机制的重要途径,目前主要有室内试验和原位试验两种。相比而言,基于环境箱的室内蒸发试验方法具有较好的应用前景;(3)土体水分的蒸发过程可划分为3个阶段:常速率、减速率和残余阶段;(4)影响土体水分蒸发的因素归纳起来可分为内部土性和外部环境因素两类,前者主要影响土体水分的传输能力,后者主要影响蒸发能量的供应强度;(5)当前关于土体水分蒸发量的计算和预测模型较多,但往往存在误差大、适应范围窄或参数难于获取等不足。基于上述认识,并结合本学科的研究背景,提出了今后该课题的研究重点和方向,包括减速率阶段的蒸发机制、土性参数与蒸发速率之间的量化关系、黏性土尤其是膨胀土中水分的蒸发和迁移机制、高精度原位土体水分蒸发试验设备的研发和构建通用型的土体水分蒸发理论模型等。

Soil moisture evaporation is one of the main processes of mass and energy exchange of soil-atmosphere, which has an important influence on soil engineering properties. It is also the direct cause of many engineering and environmental problems, however, this issue has never been taken into account in geoengineering disciplines. Based on the recent research achievements on soil moisture evaporation in other disciplines, the advances of some important aspects on this topic, i.e. soil moisture evaporation capacity determination, test method, evaporation process, influencing factors and theoretical model, are summarized and shown as follows：（1） To accurately determine the actual evaporation capacity of soil is one of the most important tasks in soil moisture evaporation study. Generally, there are two categories of methods： theory calculation and direct measurement;（2） To carry out evaporation test is an important approach to understand soil moisture evaporation process and the related mechanism. There are two categories of tests： laboratorial test and in-situ test. As compared, evaporation test by environmental chamber has better application prospect;（3） Soil moisture evaporation process can be divided into three stages： constant rate, falling rate and residual rate phases;（4） The factors influencing soil evaporation can be categorized as internal soil factors and external environmental factors. The former one mainly affects soil moisture transportation characteristics, and the latter one mainly influences evaporation energy supply intensity;（5） Many soil moisture evaporation calculation and prediction models have been proposed, however, they show some disadvantages such as large errors, narrow range of adaptation or difficulties on parameters acquisition. Based on the above understanding, and to combine with the research background of geotechnical and geological engineering, some important research topics that should be well investigated in future are proposed, including the evaporation mechanism of falling rate stage, the quantitative relationship between the soil properties and evaporation rate, soil moisture evaporation and transportation mechanisms in clayey soil especially in expansive soil, development of high precision in-situ soil moisture evaporation test apparatus and construction of universal soil moisture evaporation theoretical model.