Abstract A series of monotonic and cyclic triaxial shearing tests on Toyoura sand are simulated by discrete element method (DEM) incorporating rolling resistance. The input parameters are calibrated against laboratory triaxial test data considering different initial states and monotonic loading paths. The calibrated DEM model successfully captures the density and stress dependency of sand behavior under both monotonic and cyclic conditions. It is shown that when approaching liquefaction, contact yielding alters from sliding-dominant to rolling-dominant. The expression of mechanical redundancy index (IR) is derived considering both effects of contact sliding and rolling. The IR = 1.0 condition is shown to be a unified criterion distinguishing between solid state and liquid state upon both monotonic and cyclic liquefactions. A unique micro critical state line (CSL) is obtained in MCN-p′ plane. The cyclic resistance ratio is exponentially correlated with both the macro state parameter (ψe0) derived from the e-p′ CSL and the micro state parameter (ψMCN0) determined from the MCN-p′ CSL. The specimens with the same ψe0 may have distinct cyclic behaviors, while cyclic behaviors of specimens with the same ψMCN0 are close to each other, indicating that ψMCN0 is a more plausible state variable for characterizing the behavior of sand than ψe0.

中文翻译：

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基于临界状态土力学框架的砂土单调循环行为DEM分析

摘要 采用结合滚动阻力的离散元法（DEM）对Toyoura砂进行了一系列单调循环三轴剪切试验。考虑到不同的初始状态和单调加载路径，输入参数根据实验室三轴测试数据进行校准。校准的 DEM 模型成功地捕获了单调和循环条件下沙子行为的密度和应力依赖性。结果表明，当接近液化时，接触屈服由滑动主导转变为滚动主导。考虑到接触滑动和滚动的影响，推导出机械冗余指数（IR）的表达式。IR = 1.0 条件被证明是在单调和循环液化时区分固态和液态的统一标准。在 MCN-p' 平面中获得了独特的微临界状态线 (CSL)。循环电阻比与从 ep' CSL 导出的宏观状态参数 (ψe0) 和从 MCN-p' CSL 确定的微观状态参数 (ψMCN0) 呈指数相关。ψe0 相同的试样可能具有不同的循环行为，而ψMCN0 相同的试样的循环行为彼此接近，表明ψMCN0 是比ψe0 更可能表征沙子行为的状态变量。