Effects of cracks on evaporation process of water in soils
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摘要: 工程中的土体在干旱气候作用下易发育干缩裂隙，裂隙的存在对土体的工程性质有重要的影响。为了研究裂隙对土中水分蒸发过程的影响，在模拟干旱条件下对含裂隙土体开展了一系列室内蒸发试验。采用预制裂隙的方法，制备了一系列包含不同裂隙条数（0~3）和裂隙宽度（5，10，15 mm）的试样，基于获得的含水率、蒸发速率随干燥时间变化结果，重点分析了裂隙条数、宽度和分布特征对蒸发过程的影响机制。结果表明：①裂隙对土体水分蒸发过程有重要影响；②试样的蒸发速率和减速率阶段对应的临界含水率随裂隙条数的增加呈增加趋势，在5 mm裂隙宽度条件下，每增加一条裂隙，试样的蒸发速率增加约14%，对应裂隙面的蒸发通量约为试样表面的15%~18%；③试样的蒸发速率和裂隙面的蒸发贡献随裂隙宽度的增加亦呈增加趋势，裂隙宽度每增加1 mm，试样的蒸发速率增加约2%，当裂隙宽度从5 mm增加到15 mm时，对应裂隙面的蒸发通量从试样表面的18%增加到51%，但裂隙宽度对试样进入减速率阶段时的对应的临界含水率无影响；④裂隙分布对蒸发速率的影响主要由裂隙蒸发面和裂隙腔体内的相对湿度梯度和热量传输控制，并可能存在裂隙宽度阈值效应。Abstract: Under the action of arid climate, the soils in the engineering are prone to develop shrinkage cracks, and the existence of cracks has an important influence on the engineering properties of the soils. In order to study the effects of cracks on the evaporation process of water in the soils, a series of laboratory evaporation experiments are carried out on the soils with cracks under simulated drought conditions. A series of samples with different crack numbers (0~3) and crack widths (5, 10 and 15 mm) are prepared by using the method of prefabricated cracks. Based on the results of water content and evaporation rate with drying time, the influence mechanism of crack numbers, widths and distribution characteristics on the evaporation process is analyzed. The results show that: (1) The cracks have a significant effect on the evaporation process of water in the soils; (2) The evaporation rate and the critical water content corresponding to the falling rate stage of the samples increase with the increase of the number of cracks. Under the crack width of 5 mm, the evaporation rate of the sample increases by about 14% for each additional crack, and the evaporation flux of the corresponding crack surface is about 15%~18% of the sample surface. (3) The evaporation rate of the samples and the evaporation contribution of the crack surface also increase with the increase of the crack width. The evaporation rate of the sample increases by about 2% for every increase of the crack width of 1 mm. When the crack width increases from 5 to 15 mm, the evaporation flux of the corresponding crack surface increases from 18% to 51% of the sample surface. However, the crack width has no effects on the critical water content when the samples enter the falling rate stage. (4) The effects of crack distribution on evaporation rate are mainly controlled by the relative humidity gradient and heat transfer in crack evaporation surface and crack cavity, and there may be a threshold effect of crack width.
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Keywords:
- soil evaporation /
- crack effect /
- crack number /
- crack width /
- soil cracking /
- evaporation rate
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图 4 裂隙条数对蒸发的影响
Figure 4. Variation of (a) water content versus time; (b) evaporation rate versus time; (c) evaporation rate versus water content with different crack numbers; (d) initial evaporation rate versus crack number
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图 5 裂隙宽度对蒸发影响
Figure 5. Variation of (a) water content versus time; (b) evaporation rate versus time; (c) evaporation rate versus water content with different crack widths; (d) initial evaporation rate versus crack width
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图 6 裂隙分布对蒸发影响
Figure 6. Evaporation rate versus time and water content with different crack distributions
表 1 试样参数
Table 1 Parameters of samples
试样编号 S1 S2 S3 S4 S5 S6 裂隙条数 0 1 2 3 1 1 裂隙宽度/mm 0 5 5 5 10 15 
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