In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses.

本文提出了一种新开发的砾石-橡胶混合物（GRMs）三维离散元模型（DEM），即DEM4GRM，能够准确描述GRMs宏观尺度剪切响应（从小变形到大变形）。介绍了一种直剪箱装置。刚性砾石颗粒被建模为简单的多形状团块，而软橡胶颗粒则使用可变形的 35 球体心立方簇来建模。制备具有不同体积橡胶含量的混合物（VRC) 在 0、10、25、40 和 100% 下，在 30、60 和 100 kPa 垂直应力下静态压缩，然后通过密切模拟参考实验室测试程序进行剪切。在整个剪切过程中仔细检查了诸如织物、法向和切向力各向异性等微观因素的变化，并通过适用于 GRM 的新型微观机械关系进行了描述。此外，对强力链进行仔细检查，以识别从刚性到软颗粒骨架的过渡，并深入了解 GRM 的载荷传递和变形机制。结果表明，剪切过程中织物的发展和力各向异性与 GRM 的宏观剪切强度密切相关，并且强烈依赖于VRC. 此外，强力链似乎主要由砾石 - 砾石接触（导致类似刚性的机械行为）高达VRC  = 30％，以及超过VRC的橡胶 - 橡胶接触（导致类似软的机械响应）形成 = 60%。或者，在 30% < VRC  < 60% 时，砾石-橡胶接触在强力网络中占主导地位，并观察到中间机械行为。这与在宏观和微观机械响应中观察到的行为趋势一致。