颗粒结构及雪崩前的异质变形
Granular structure and heterogeneous deformation preceding avalanches
- Navier, CNRS, Univ Gustave Eiffel, ENPC, Institut Polytechnique de Paris（纳维埃实验室，法国国家科学研究中心，巴黎-沙隆恩斯特·盖非尔大学，国立桥梁与道路学校，巴黎理工学院）
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中文总结 AI 辅助
本研究通过实验揭示颗粒堆积雪崩前的前兆活动受制备结构与加载方向兼容性影响，但位移衰减和应变标度等空间特征保持稳健，并基于两态模型量化了局部异质性的影响。
中文摘要 AI 辅助
颗粒堆积在雪崩发生前会经历间歇性重排，称为前兆。通过在倾斜颗粒层中进行颗粒尺度追踪，我们实验证明前兆的数量和复发频率会随着制备过程中继承的各向异性结构与后续加载方向之间的兼容性而变化。制备过程还改变了迁移前沿的传播，迁移前沿定义为堆积发生可测量位移的区域：频繁的前兆产生小的渐进推进，而罕见的前兆则涉及更大的扩展。相比之下，若干特征在不同方案中保持不变。系综平均位移总是随深度以约四个颗粒直径的尺度呈指数衰减，而局部剪切应变方差则与平均应变遵循共同的二次标度关系。一个两态模型表明，无论堆积结构如何，局部应变异质性影响约四分之一的单元胞，叠加在指数应变分布之上。所报告的结果将依赖制备的前兆活动与雪崩前变形的稳健空间特征区分开来。
英文摘要
Granular packings undergo intermittent rearrangements, known as precursors, before avalanche onset. Using grain-scale tracking in an inclined granular layer, we show experimentally that the number and recurrence of precursors change with the compatibility between the anisotropic structure inherited from preparation and the subsequent loading direction. Preparation also modifies the propagation of the mobility front, defined as the region in which the packing undergo measurable displacement: frequent precursors produce small progressive advances, whereas rare precursors involve larger extensions. By contrast, several features remain unchanged across protocols. The ensemble-averaged displacement always decays exponentially with depth over approximately four grain diameters, while the local shear-strain variance follows a common quadratic scaling with the mean strain. A two-state model suggests that, regardless of the packing structure, local strain heterogeneities affect approximately one quarter of the elementary cells, superimposed on the exponential strain profile. The reported results separate preparation-dependent precursor activity from the robust spatial features of the deformation preceding avalanches.
