高频振动下岩土颗粒材料动力行为及细观机理

Dynamic Behavior of Granular Materials under High Frequency Loading and the Meso⁃Mechanism

针对高频振动条件下岩土颗粒材料动力响应放大的现象,采用离散元法开展了一系列动双轴数值试验,分析了不同荷载频率下岩土颗粒材料的动力行为及其细观特征.试验结果表明:对于模拟的岩土颗粒材料,在加载频率为30~40 Hz时的动力变形尤其明显,加载过程中塑性变形快速发展,试件内部形成“八”字型剪切带,动刚度显著降低.提出了“竖向分布系数”描述试件内部的局部变形规律,并结合颗粒细观受力特征,探究了试件变形加剧和刚度弱化的细观机理.研究发现相较20 Hz和60 Hz工况,加载频率为40 Hz时试件中下部区域的局部动变形振动幅值明显增大,颗粒处于高度动力非平衡态,颗粒体系的排列结构和接触力剧烈调整,使得试件变形加剧、承载性能显著弱化.

The dynamic response of geotechnical granular materials may be amplified when subjected to high-frequency loading.To explore this phenomenon,a series of dynamic biaxial numerical tests were conducted on a granular material utilizing the discrete element method(DEM).The investigation focuses on the dynamic deformation behavior and meso-mechanical mechanisms under various loading frequencies.The findings reveal that the dynamic response is most pronounced at loading frequencies between 30 Hz and 40 Hz for the selected geotechnical granular materials.This response is characterized by rapid plastic deformation,the formation of two disjoint shear bands within the test specimen,and a significant reduction in dynamic stiffness.Furthermore,an index of vertical distribution coefficient was proposed to describe the local deformation law of the specimen.Along with meso-mechanical considerations,the mechanism of deformation aggravation and stiffness degradation were discussed.It has been found that compared with 20 Hz and 60 Hz loading conditions,the deformation amplitude of local areas in the middle and lower parts of the sample noticeably increases under the 40 Hz loading condition.The forces on particles were at highly non-equilibrium state,leading to the dramatically adjustment in the meso-structure and contact force network.The particle contact network may have frequent failure and reconstruction,resulting in rapid accumulation in plastic deformation and a loss in bearing capacity at the macro scale.