An analysis of rainfall infiltration of expansive soil slope based on the finite element software custom constitutive model
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摘要:
降雨条件下，边坡土体吸水软化造成抗剪强度降低是引发边坡失稳的重要因素之一。雨水在边坡土体中的入渗过程是动态变化的，土体含水率（饱和度）也会随之发生持续变化，因此，研究土体抗剪强度在动态环境下的变化规律，对实时评价降雨工况下土体边坡的稳定性具有重要意义。文章以贵州省尖山营地区的膨胀土为研究对象，基于非饱和土强度理论，结合室内剪切试验数据分析了膨胀土的抗剪强度指标与土体含水率的关系，提出了以含水率为变量的抗剪强度公式；基于ABAQUS有限元软件平台的二次开发技术编写了USDFLD子程序，结合室内试验得出的土体抗剪强度变化规律，分析了降雨条件下土体含水率变化引起的强度衰减与土体重度变化对膨胀土边坡稳定性的影响。结果表明：随膨胀土含水率增加，土中颗粒吸水膨胀，颗粒间距缩小，矿物颗粒间的黏结作用逐渐增大，直至集合体空隙充水，吸力减小，黏结作用迅速减弱；膨胀土的抗剪强度总体呈递减趋势，其中，黏聚力先增后减，内摩擦角递减。应用ABAQUS有限元软件的二次开发技术可实现土体参数随含水率的动态变化而变化，为降雨条件下非饱和土边坡的有限元分析提供了一种新的技术手段。
Abstract:Under the condition of rainfall, the decrease in shear strength of a slope is one of the important factors that lead to the slope instability. Infiltration of rainwater into the slope is a dynamic process, and the water content or saturation of soil will change continuously. Therefore, it is of great significance to study the shear strength of soil under dynamic environment for real-time evaluation of the stability of soil slope under rainfall conditions. Based on the strength theory of unsaturated soil, this paper takes the expansive soil in the Jianshanying area of Guizhou Province as the object, combines the shear test data to establish the fitting relationship between the shear strength index and water content of the expansive soil, and puts forward the shear strength formula with water content as the variable. Based on the secondary development technology of ABAQUS platform, USDFLD subroutine is compiled to import the shear strength formula of the Jianshanying expansive soil, and the influence of strength attenuation and gravity change caused by the change of soil moisture content on the stability of the expansive soil slope under the condition of rainfall are also explored. The results show that with the increasing water content of the expansive soil, the particles in the soil expand by the absorbing water, the particle spacing decreases, and the adhesion between the mineral particles increases gradually. Until the water filling suction of the aggregate space decreases, the adhesion decreases rapidly, and the shear strength of the expansive soil decreases generally, in which the cohesion increases first and then decreases, and the internal friction angle decreases. The secondary development technology of ABAQUS software can realize the relationship of soil parameters with the change of water content, which provides a new technical means for the finite element analysis of unsaturated soil slope under the condition of rainfall.
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表 1 土体材料参数
Table 1. Soil material parameters
重度/
弹性模量/
MPa泊松比
有效黏聚力/
kPa有效内摩擦角/
(°)饱和渗透系数/
18 100 0.27 14.02 13 0.000369 
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表 2 Van-Genuchten模型参数
Table 2. Van-Genuchten model parameters
α n 0.4413 0.0648 0.002368 1.911
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表 3 边坡稳定系数
Table 3. Slope stability coefficient
降雨历时/h 稳定系数 说明 导入子程序 不导入子程序 0 1.45 1.45 初始工况 12 − 0.994 塑性面贯通 21 0.997 − 24 0.927 0.845 失稳
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