Microscopic insight into the soil fabric during load-unload correlated with stress waves
Microscopic insight into the soil fabric during load-unload correlated with stress waves
复制标题
加载-卸载过程中与应力波相关的土壤结构的微观观察
DOI：
10.1007/978-3-031-11898-2_204
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Kuwano Reiko
中科院分区：
文献类型：
--
作者：
Li Yang;Otsubo Masahide;Kuwano Reiko
土壤具有复杂的接触网络（即土壤结构），它影响力学特性（例如刚度各向异性、剪切强度）并进一步决定岩土工程的性能。传统的土壤实验室测试可以给出宏观尺度的力学响应作为物理相关性，而离散元法 (DEM) 已被用作数值工具来深入了解土壤结构等微观尺度的力学特性。在这项研究中，实验室元件测试是使用球形玻璃珠在选定的峰值前应变范围内进行多次加载-卸载反转循环进行的，其中在加载过程中连续测量应力波。采用球形粒子的 DEM 来模拟等效加载-卸载反转和波传播。根据实验和 DEM 结果，发现当加载-卸载循环处于低应力水平时，压缩速度 (Vp) 和剪切波速度 (Vs) 近似可逆，而在较高应力水平下可以观察到这两种速度显着降低。使用 DEM 探讨了加载-卸载反转过程中土壤结构各向异性的变化；织物各向异性显着增加，超过应力比阈值 1.8，并且在随后的卸载过程中无法完全恢复。研究发现，织物各向异性与峰值前阶段的波速比 (Vp/Vs) 呈线性相关，尽管这两个量分别受到给定应力状态的影响。
Soils have a complex contact network (i.e. soil fabric), which affects the mechanical characteristics (e.g. stiffness anisotropy, shear strength) and further determines the performance in geotechnical constructions. Conventional laboratory tests on soils can give macro-scale mechanical responses as a physical relevance, while the discrete element method (DEM) has been used as a numerical tool to gain insights into micro-scale mechanical characteristics such as soil fabric. In this study, laboratory element tests are conducted using spherical glass beads subjected to several cycles of load-unload reversals at selected pre-peak strain ranges, where stress waves are continuously measured during the loading process. DEM is adopted using spherical particles to simulate the equivalent load-unload reversals and wave propagations. Based on the experimental and DEM results, the compression velocity (Vp) and shear wave velocity (Vs) are found to be approximately reversible when the load-unload cycles are at low stress levels, while a significant reduction in both velocities can be observed at higher stress levels. The variation of soil fabric anisotropy during load-unload reversals is explored using DEM; the fabric anisotropy increases markedly beyond a stress ratio threshold of 1.8 and cannot be fully recovered during the subsequent unloading process. Fabric anisotropy is found to be linearly correlated with wave velocity ratio (Vp/Vs) at the pre-peak stage, although both quantities are respectively affected by the given stress states.