Abaqus选择库伦摩尔塑性模型的时候,需要选择摩擦角和剪胀角。摩擦角物理意义明确,但何为剪胀角?如何影响结果呢?(这两个问题,暂无统一解)
The angle of dilation controls an amountr of plastic volumetric strain developed during plastic shearing and is assumed constant during plastic yielding【剪胀角控制塑性体应变,一般假设在塑性变形过程中保持不变】. The value of ψ = 0 corresponds to the volume preserving deformation while in shear.【剪胀角=0,即体积不变性】
Clays (regardless of overconsolidated layers) are characterized by a very low number of dilation (ψ ≈ 0)【黏土剪胀角约为0】. As for sands, the angle of dilation depends on the angle of internal friction【砂土剪胀角约等于内摩擦角】. For non-cohesive soils (sand, gravel) with the angle of internal friction φ > 30° the value of dilation angle can be estimated as ψ = φ - 30°【对于内摩擦角>30的情况,剪胀角=内摩擦角-30】. A negative value of dilation angle is acceptable only for rather loose sands【剪缩仅针对松软砂土】. In most cases, however, the assumption of ψ = 0 can be adopted.
剪胀角的定义
,其中为剪胀角,dv为体积变量,dh为高度变量,具体如下图。
PS 剪胀角应该放在“本构关系”里理解。
剪胀角的选择
大多数岩土工程分析中选择了两种极端情况:
- 关联流动法则(剪胀角ψ=摩擦角)
- 非关联流动法则(剪胀角ψ=0)
关联流动 法则意味着土体在剪切的过程中可以产生无限制的体积膨胀现象,非关联流动法则ψ=0则认为土体是不可膨胀的,由此获取极限荷载。孔位学等推荐剪胀角取摩擦角的一半[4]。
参考文献
[1] 张培文,陈祖煜.剪胀角对求解边坡稳定的安全系数的影响[J].岩土力学,2004(11):1757-1760.
[2]刘俊芳,李驰.基于莫尔-库伦模型探讨剪胀角的取值问题[J].内蒙古工业大学学报(自然科学版),2015,34(04):293-297.
[3]赵星光,蔡明,蔡美峰.岩石剪胀角模型与验证[J].岩石力学与工程学报,2010,29(05):970-981.
[4]孔位学,芮勇勤,董宝弟.岩土材料在非关联流动法则下剪胀角选取探讨[J].岩土力学,2009,30(11):3278-3282.