Abstract We employ a hierarchical multiscale modeling approach to investigate the transitions of localized deformation patterns in high-porosity sandstone subjected to sustained shear to understand their underlying physics. The multiscale approach is based on hierarchical coupling between finite element method (FEM) with discrete element method (DEM) to offer cross-scale predictions for granular rocks without assuming phenomenological constitutive relations. Our simulations show that when a high-porosity sandstone specimen is subjected to continuous deviatoric loading, compaction bands may occur and evolve, featuring a steady movement of the compaction front (i.e. the boundary between the compaction band and the rest uncompacted zone). The specimen reaches a homogeneous state of reduced porosity when the compaction fronts traverse the entire specimen. A re-hardening response is initiated in the specimen under further shear, which is followed by a shearing dominating stage with the emergence of shear bands. The material responses inside the ultimate shear bands approach a “steady state” of constant porosity and stress ratio. Cross-scale analyses reveal that debonding and pore collapse are dominant mechanisms for the compaction stage of the specimen, and debonding and particle rotation dictate the physics for the shear banding stage. The transitions from compaction to shear banding occurs due to the degradation of the cohesive contact network and significant reduction in porosity. There are limited number of interparticle bonds remaining at the “steady state” under sustained shear, with a preferential direction perpendicular to the loading direction, leading to a higher steady void ratio than the critical state void ratio of non-cohesive sand.

中文翻译：

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高孔隙度砂岩局部变形模式转变：多尺度分析的见解

摘要 我们采用分层多尺度建模方法来研究高孔隙度砂岩在持续剪切作用下局部变形模式的转变，以了解其基本物理特性。多尺度方法基于有限元法 (FEM) 与离散元法 (DEM) 之间的分层耦合，可在不假设现象学本构关系的情况下为粒状岩石提供跨尺度预测。我们的模拟表明，当高孔隙度砂岩试样受到连续偏载时，压实带可能出现并演化，其特征是压实前沿（即压实带和其余未压实带之间的边界）的稳定运动。当压实前沿穿过整个试样时，试样达到孔隙率降低的均匀状态。试样在进一步剪切下开始重新硬化响应，随后是剪切带出现的剪切主导阶段。极限剪切带内的材料响应接近孔隙率和应力比恒定的“稳态”。跨尺度分析表明，脱粘和孔隙坍塌是试样压实阶段的主要机制，脱粘和粒子旋转决定了剪切带阶段的物理特性。由于内聚接触网络的退化和孔隙率的显着降低，发生从压实到剪切带的转变。