脱水过程土壤体积质量、含水率、吸力的关系

Relationships between Bulk Density,Water Content and Matric Potential of Soils During Drying Process

【目的】分析土壤脱水过程中的收缩特性。【方法】采用离心机法测定了辽宁砂壤土(LN)、云南黏壤土(YN)、陕西黏壤土(SX)和山东壤土(SD)的土壤水分特征曲线,并采用Brooks-Corey模型进行了拟合;同时对脱水过程中土壤收缩特性进行了研究,定量分析了土壤体积质量、含水率、吸力之间的关系。【结果】对于LN、YN、SX和SD土样,(1)在土壤脱水过程中,含水率随吸力增加而减小;当土壤较干和接近饱和含水率时,减小速率较小,而在二者之间时减小速率较大;(2)基于Brooks-Corey土壤水分特征曲线模型和土壤收缩线性模型,土壤体积质量和吸力呈幂函数关系;(3)土壤脱水过程导致含水率降低、体积质量增加,二者呈负相关关系,土壤的收缩过程大致可分为伪饱和段、结构段和超正常段等3个直线型收缩段;Logistic模型具有较高拟合精度且可以使得土壤收缩特征拟合曲线具有连续性。【结论】土壤脱水过程中,其体积质量与吸力呈现幂函数关系,而含水率与体积质量可采用Logistic模型量化表征。

【Objective】Wetting-drying cycles affect soil physical properties and this paper is to investigate how the bulk density, water content and matric potential of soils are correlated when the soils are shrunken during drying process.【Method】Soil samples were taken from Liaoning（sandy loam）, Yunnan（clay loam）, Shaanxi（slay loam） and Shandong Provinces（loam）. We first measured the water release curve using the centrifuge method for each soil and then fitted it to the Brooks-Corey formula. We thereafter investigated the soil shrinkage during drying process and analyzed the relationship between bulk density, water content and matric potential of the soils.【Result】The soil moisture decreased with an increase in matric potential, and the decreasing rate decreased first,then increased, followed by a decrease with the matric potential increasing from 0 to 7 000 cm. A power function was found between the soil bulk density and the matric potential based on the Brooks-Corey formula for water retention and the linear model for soil shrinkage. The decrease in water content due to increase in bulk density can be described by the soil shrinkage curve which is piecewise linear in the pseudo-saturated stage, the structural change stage and the super-normal stage, each corresponding to a specific matric potential range depending on soil types.【Conclusion】The relationship between the bulk density and the matric potential follows a power and can be fitted to the logistic model.