非饱和土等效时间流变模型

An equivalent-time rheological model of unsaturated soil

摘要:

为了理论分析流变速率效应力学特性,需要建立非饱和土流变模型.首先把非饱和土屈服面分为LC和SI屈服面。其次根据LC屈服面的压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率公式,结合巴塞罗那屈服方程和相关联流动法则,获得LC屈服面的三维流变速率方程,揭示了本文与Gennaro-Pereira提出的LC后继屈服面方程的异同。再次,根据SI屈服面的吸力压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率方程.最后,把LC和SI屈服面的流变速率方程与弹性方程相结合,建立非饱和土等效时间三维弹黏塑性模型.当不考虑流变速率效应时,LC和SI流变屈服方程可以退化到巴塞罗那模型的塑性屈服方程.理论分析了非饱和土一维流变特性,并与土工试验数据进行对比,两者较为吻合。三轴加载条件下的流变特性数值分析结果表明,按不同方式施加到同一恒载时,随着恒载维持时间的增长,不同加载方式引起的体积流变趋向一致,但剪切流变有较明显的差别.

Abstract:

To theoretically analyze the mechanical behaviors of rheological rate effect, the rheological model of unsaturated soil should be formulated. First, the yield surfaces of unsaturated soil are divided into LC and SI yield surfaces. Second, based on the compression creep formula of the LC yield surface, the corresponding rate of viscoplastic volumetric strain is formulated by the equivalent-time method.Combined with Barcelona yield equation and the associated flow law, the three-dimensional rheological rate equation of the LC yield surface is obtained.Differences and similarities between the LC subsequent yield equation of Gennaro-Pereira are discussed. Then, based on the suction-induced compression creep formula of SI yield surface,the corresponding viscoplatic volumetric strain rate is formulated by the equivalent-time method. Finally, the equivalent-time three-dimensional elastic viscoplastic model of unsaturated soil is built combining the rheological rate equations of LC and SI yield surfaces with elastic equation.When the rheological rate effect is ignored, LC and SI rheological yield equations can be degenerated into the corresponding plastic yield equations of Barcelona model. One-dimensional rheological behaviors are theoretically analyzed,and the theoretical predicts and the soil test data are in relatively good agreement. The numerical analysis results of rheological behaviors under three-axial loading condition show that when the same dead loading is applied by several ways, along with the duration of dead loading, the rheological volumetric strains at different ways will tend to equalise value, but the rheological shear strains will have obviously different values.