基于离散元法的真三轴应力状态下砂土破碎行为研究

基于可破碎三维离散颗粒模型模拟了一系列常规三轴试验与真三轴试验,研究了砂土在真三轴应力状态下的破碎行为。数值调查主要关注试样的应力应变特性、级配及相对破碎率的演化。随着围压增大,颗粒破碎率增大,试样应变软化特性和剪胀性逐渐减弱,而超过临界高围压后,由于固结中颗粒大量破碎,试样剪胀性反而增强。真三轴试验中,试样偏应力比峰值均随中主应力参数b值增大而减小。由于破碎随b值增加而明显增大,试样剪胀性随b值增大而逐渐减弱。试样内摩擦角φ随围压增大而减小,其演化关系基本满足对数关系;内摩擦角随b值增大先增大后减小,Lade-Duncan准则较为适合描述其变化规律。此外,试样相对破碎率增大的速率随围压和轴向应变增大而逐渐降低,暗示试样最优终极级配的存在,且相对破碎率与试验输入能量之间存在唯一的双曲线关系。

Breakage behavior of sand under true triaxial stress based on discrete element method

A series of triaxial compression tests and true triaxial tests based on discrete element method are conducted numerically to investigate the particle breakage behavior of granular materials under triaxial stress conditions. The numerical investigation mainly focuses on the stress-strain behavior, the evolution of the particle-size distribution and relative breakage of the crushable granular assembly. As the confining pressure increases, it is found that the dilatancy and strain softening of granular assembly decrease, which is related to the increase in the particle breakage. Beyond a higher confining pressure, the volumetric dilatation starts to increase, caused by the increase of the particle breakage during consolidation. In true triaxial tests, the peak stress ratio decreases with the increasing intermediate principal stress ratio b. And the increase of b results in the decrease of dilatancy, which stems from the distinct increasing compaction caused by breakage with the increasing b. The internal friction angle φ decreases with the increasing confining pressure, which conforms to a logarithmic relationship, and φ increases first and then decreases with the increasing b, which conforms to the Lade-Duncan failure model. In addition, the increment of the increasing relative breakage declines with the increasing confining pressure and axial strain, which implies the existence of the optimum distribution of granular assembly. The relationship between the particle breakage and the total input energy during tests is found to conform to a unique hyperbolic correlation.