粗粒土的非共轴性及其离散元数值模拟

以粗粒土为原材料的土石坝在蓄水期或者水位突降的情况下,粗粒土的主应力轴将产生旋转,从而出现土体单元主应力方向和主应变率方向的非共轴现象,而传统的弹塑性本构模型基本上是建立在大三轴试验结果的基础上,并不能考虑粗粒土的非共轴性。本文将传统的弹塑性本构模型三维化,引入三维非共轴塑性流动理论,建立了粗粒土的非共轴本构模型,该模型对粗粒土的单剪试验进行了数值模拟,预测了在单剪过程中主应力方向和主应变率方向的变化规律。最后,运用离散单元法(二维颗粒流程序PFC2D)对粗粒土的非共轴性进行验证并进行了细观分析。研究结果表明,本文模型的计算结果和试验结果较为一致,并能较好地描述粗粒土的非共轴现象。

Non-coaxial behavior of coarse granular aggregates simulated by DEM

In the ponding period of embankment dam or when the water level varying instantaneously, the rotation of principal stress axis for coarse granular aggregates will take place, which makes the direction of principal stress and the direction of principal plastic strain rate non-coaxial. However, the classical elasto-plastic constitutive models are generally based on large triaxial tests, they can not describe the non-coaxial phenomena. Thus a modified non-coaxial elasto-plastic model of coarse granular aggregates was proposed by introducing a non-coaxial item, which was expressed in three-dimensional format. Series of numerical simulation of simple shear tests were carried out, the results showed that the proposed non-coaxial constitutive model could describe the mechanical characteristics of coarse granular aggregates preferably, could predict the variations of principal plastic strain rate directions and principal stress directions reasonably. The non-coaxial behavior of coarse granular aggregates was verified by using particle flow code in two dimensions.