颗粒形状和倾角对颗粒柱坍塌影响的超二次曲面离散元模拟

    Superquadric discrete element simulation for influence of particle shape and orientation on granular column collapse

    • 摘要: 岩土体中颗粒形状各异且可能具有定向排列,明确颗粒形状和倾角对颗粒柱坍塌特性的影响对地质灾害防治有重要意义。基于超二次曲面离散元法模拟颗粒柱的坍塌过程,并着重分析颗粒形状(长宽比A和块度B)及初始颗粒长轴倾角θ对颗粒柱坍塌特性的影响并探究其物理机制。研究结果表明:相对于A为1(各向等长)的情形,A越大(越细长)或越小(越扁平),颗粒柱坍塌的最终跑出距离减小而最终堆积高度增加;随着B增加(棱角越突出),颗粒柱坍塌的最终跑出距离减小而最终堆积高度增加;θ≈0°(近水平)的颗粒柱的最终跑出距离明显小于其它颗粒倾角的情形,且呈现出先在侧向自由面局部颗粒被挤出、而后位于上部的颗粒逐渐滑落的运动模式;对于低柱,其运动模式以滑移为主,θ≈135°(近堆积后斜坡的顺坡向)的颗粒柱的最终跑出距离最远;对于高柱,前期垮塌效应明显,θ≈90°(近直立)的颗粒柱的最终跑出距离最远;不同颗粒形状和倾角对颗粒柱坍塌特性的影响与能量的转化演变过程及细观结构特征密切相关。

       

      Abstract: The shape of rock and soil particles is distinct and their orientation may prefer a certain direction, and determining the influence of particle shape and orientation on the characteristics of granular column collapse is of great significance to geological disasters prevention. The collapse process of granular columns is simulated with the superquadric discrete element method, and the influence of particle shape (aspect ratio A and blockiness B) and initial orientation angle θ of long axis on the collapse characteristics of granular column is analyzed, and further the underlying physical mechanism is explored. The results show that, compared with the case A=1 (isotropic), the collapse of particles with larger A (elongated) or smaller A (platy) results in shorter final runout distance and increases the deposit height. The collapse of particles with larger B (more angular) results in shorter runout distance and higher deposit height. The column with θ ≈ 0° (near horizontal) particles produces an obviously smaller final runout distance, and moves in a way that some particles being first squeezed out from the lateral free surface followed by the gradual slide of particles in the upper parts. For short column, the flow regime is slip-dominant, and the collapse of particles with θ ≈ 135° (near the orientation of subsequent accumulation slope) produces the longest final runout distance. For tall column, the early falling effect is obvious, and the collapse of particles with θ ≈ 90° (nearly upright) has the longest final runout distance. The influence of different particle shapes and orientation angles on the characteristics of granular column collapse is closely related to the transformation process of energy and the meso-structure.

       

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