砂土中浅埋圆或螺旋形锚板上拔承载机理数值分析

本文基于欧拉-拉格朗日单元耦合分析方法,并采用可考虑应变软化的改进Mohr-Coulomb弹塑性本构模型,对砂土中圆锚拉拔过程进行数值模拟。在与单盘螺旋锚离心机试验结果对比验证数值模型有效性的基础上,探讨了不同密实度砂土中锚板的拉拔破坏机理,并分析了浅埋圆锚的破坏滑裂面形式,以及滑裂面上土体强度参数及侧压力分布规律等。数值结果表明,滑裂面上土压力系数及内摩擦角并非常值,土压力系数从锚盘边缘开始直线上升,至0.2D(盘径)高度时达到峰值,而后呈指数衰减至某一稳定值；对于松及中密砂土,滑裂面上等效内摩擦角可采用Davis折减公式确定,对于密砂,Davis折减公式会高估等效内摩擦角(约3°)。基于上述分析结果,最终提出了浅埋圆形及螺旋形锚板的上拔承载力理论计算方法,同时建议了现有理论计算公式的适用条件,相关成果可为工程应用提供一定参考。

Numerical Analysis of Uplift Bearing Mechanism for Shallow Circular or Helical Anchor Plate in Sand

A numerical study combining coupled Eulerian-Lagrangian method to large deformation analysis and modified Mohr-Coulomb elastic-plastic constitutive model that can describe the soil behavior of strain softening has been performed to investigate the pullout mechanism of circular or helical anchor plates in sand. The validity of the numerical model has been established through the comparison against the centrifugal tests of single-helix anchors. The uplift failure mechanism of circular anchors in sand with different compactness is then investigated. The failure modes, distributions of normal stress and changes of soil strength along failure surfaces in loose, medium and dense sands have been analyzed. It is demonstrated that the coefficients of lateral earth pressures and the friction angles along the failure surface are not constant. The coefficient of lateral earth pressure rises linearly from the edge of the plate, up to the peak value at about 0.2D (plate diameter), and then decreases exponentially to a stable value. The equivalent friction angle along the failure surfaces in loose and medium sand can be determined by the reduction formula proposed by Davis, and it will be overestimated about 3°in dense sand. Furthermore, a theoretical calculation method for the uplift capacity of shallow circular or helical anchor plates is proposed based on the above analysis. Meanwhile, the comparison among several existing theoretical formulas has been made, and the applicability for each formula has been proposed, which can provide reference for engineering design.