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Sciences in Cold and Arid Regions ›› 2020, Vol. 12 ›› Issue (3): 125-133.doi: 10.3724/SP.J.1226.2020.00125

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A modified numerical model for moisture-salt transport in unsaturated sandy soil under evaporation

Wei Wen1,2,YuanMing Lai1,2(),ZheMin You1   

  1. 1.State Key Laboratory of Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China
    2.University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2019-12-09 Accepted:2020-05-26 Online:2020-06-30 Published:2020-06-29
  • Contact: YuanMing Lai E-mail:ymlai@lzb.ac.cn

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Abstract:

Soil salinization, caused by salt migration and accumulation underneath the soil surface, will corrode structures. To analyze the moisture-salt migration and salt precipitation in soil under evaporation conditions, a mathematical model consisting of a series of theoretical equations is briefly presented. The filling effect of precipitated salts on tortuosity factor and evaporation rate are taken into account in relevant equations. Besides, a transition equation to link the solute transport equation before and after salt precipitation is proposed. Meanwhile, a new relative humidity equation deduced from Pitzer ions model is used to modify the vapor transport flux equation. The results show that the calculated values are in good agreement with the published experimental data, especially for the simulation of volume water content and evaporation rate of Toyoura sand, which confirm the reliability and applicability of the proposed model.

Key words: moisture-salt transport, precipitated salt, Pitzer ions model, relative humidity, evaporation rate

Figure 1

Salt layer containing soil in Qaidam Basin"

Table1

Parameters values employed in numerical simulation"

ParametersMasa loamy sandToyoura sandUnitProperties
θs0.430.443m3/m3Porosity
θr0.031-m3/m3Residual volumetric water content
α1-4.2-2.651/mSoil water characteristic curve parameter
α2--2.11/mSoil water characteristic curve parameter
w-0.748-Soil water characteristic curve parameter
n11.3733.6-Soil water characteristic curve parameter
n2-1.84-Soil water characteristic curve parameter
m0.32--Soil water characteristic curve parameter
φ0-1×10-5-mResidual matric head
φ-0.75-0.4mInitial matric head
KS5.28×10-60.2×10-4m/sSaturated hydraulic conductivity
ak-1.57-Relative permeability parameter
bk-0.023-Relative permeability parameter
λ0.00140.0023mDispersity
T298.15298.15KTemperature
ra9064s/mAerodynamic resistance
C033kg/m3Initial salt concentration
Csat231231kg/m3Salt solubility
RHa0.250.4-Air relative humidity

Figure 3

Changes of relative Humidity with matric head and solute concentration"

Figure 2

Soil water characteristic curve for Masa loamy sand and Toyoura sand"

Figure 4

The osmotic coefficient of solution at different solute concentration"

Figure 5

Schematic diagram of the process of precipitated salt filling the soil pores"

Figure 6

Comparison between the measured and predicted evaporation rate for both soils"

Figure 7

Comparison between the measured and predicted volumetric water contents"

Figure 8

Concentration distributions during the course of evaporation for different sands"

Figure 9

Precipitated salt in soils at different times for both sands"

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