胶结砂土强度特性的真三轴试验离散元分析

doi:10.13722/j.cnki.jrme.2017.1464

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摘要采用三维离散元法从宏微观尺度研究胶结砂土在真三轴试验条件下的强度特性。首先，将一个已有的三维胶结接触模型引入到离散元程序中，对胶结砂土数值试样进行真三轴试验离散元模拟(平均应力p保持不变，包括结构屈服前p = 100 kPa和屈服后p = 800 kPa)；然后，对比分析离散元模拟结果和室内试验结果，并验证已有的胶结材料破坏准则；最后，从微观尺度对强度特征给予机制性分析。结果表明：当p小于结构屈服应力py时，应力–应变关系表现为显著的应变软化，当p＞py时，应力–应变关系则呈现为应变硬化现象，且均受中主应力系数b的影响。归一化的峰值强度qpeak随b增加而逐渐减小，该变化规律与已有室内试验结果符合较好。Modified Lade-Duncan准则可以较好地预测p = 100，800 kPa时的峰值强度，Extended SMP准则能较好地预测p = 100 kPa时的峰值强度，但高估了p = 800 kPa时的峰值强度。在微观尺度上，胶结试样的宏观力学特性主要受强接触点控制；随b增加，颗粒间法向接触力分布逐渐不均匀，导致胶结材料强度降低。

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关键词 ：土力学, 胶结砂土, 强度, 离散元, 真三轴, 组构

Abstract：This paper presented three-dimensional(3D) distinct element method(DEM) at the micro- and macro- scale to investigate the strength behaviour of cemented sands in true triaxial tests. A DEM program incorporating a 3D bond contact model was used to simulate the true triaxial tests on cemented specimens under two mean stresses(i.e.，pre-yield and post-yield stresses，100 and 800 kPa，respectively)，and the DEM results were compared with the available experimental data. The underlying mechanism of the strength behaviour was discussed at the microscopic scale. The results show that，when the applied mean stress is lower than the structural yield stress，the stress-strain relationships exhibit obvious strain softening，and that，when the applied mean stress exceeds the structural yield stress，the strain hardening occurs. The stress-strain relationships are affected by the intermediate stress ratio. As the intermediate stress ratio increases，the normalized peak strength decreases gradually，which is in agreement with the experimental data. The modified Lade-Duncan failure criterion can predict the peak strength under p = 100 kPa and 800 kPa，while the extended SMP failure criterion can predict the peak strength under p = 100 kPa，but overestimate the peak strength under p = 800 kPa. At the microscopic scale，the macroscopic mechanical responses of cemented sands are primarily controlled by the contacts transmitting greater-than-average forces within the whole specimen. As the intermediate stress ratio increases，the distribution of the normal contact forces tends to be non-uniform，which leads to lower strength.

Key words： soil mechanics cemented sands strength distinct element method true triaxial test fabric

引用本文:

张伏光1，2，3，4，蒋明镜3，4，5. 胶结砂土强度特性的真三轴试验离散元分析[J]. 岩石力学与工程学报, 2018, 37(6): 1530-1539.
ZHANG Fuguang1，2，3，4，JIANG Mingjing3，4，5. Analysis of the strength behaviour of cemented sands in true triaxial test with distinct element method. , 2018, 37(6): 1530-1539.

链接本文:

http://www.rockmech.org/CN/10.13722/j.cnki.jrme.2017.1464 或 http://www.rockmech.org/CN/Y2018/V37/I6/1530

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