高频低幅振动下颗粒材料抗剪强度衰减细观机理研究

Shear resistance reduction of granular materials subjected to highfrequency and low-intensity vibration:A micro-mechanical study

高速铁路速度的进一步提升,需要解决轨下土工基础在高频振动作用下的稳定性问题.前期通过试验研究发现,即使在动应力水平相对较低的条件下,高频振动作用仍会导致颗粒材料出现流态化、强度衰减等一系列区别于低频振动的现象.这些现象的力学机理目前尚未完全明确,不利于未来更高速铁路的轨下土工基础设计.结合离散元数值模拟开展了双轴试验,分析了高频低幅振动下力链数量、各向异性及遗传颗粒等细观指标的演化规律,量化了颗粒材料中承载主体骨架结构的发展变化.结果表明,颗粒材料宏观偏应力的发展、波动等与细观力链的演化规律表现出较强的一致性;高频低幅振动作用下骨架结构的变异程度与抗剪强度衰减存在线性关系,骨架结构变异越大,抗剪强度衰减越大.

The stability performance of sub-rail geotechnical structures under high-frequency vibration is an important aspect of further enhancing the travel speed of high-speed trains.In our previous experimental study on the dynamic behaviors of granular materials,fluidization and shear resistance reduction were observed during high-frequency vibration(even with relatively low vibration intensity),which are different from the dynamic behaviors under low-frequency vibration.The mechanism of the phenomenon owing to high-frequency vibration is still unclear,making the design of sub-rail geotechnical structures for future higher-speed railway lines difficult.Hence,a biaxial test is conducted via DEM simulation to obtain the variation of force chain quantity,anisotropy,and the ratio of inherent particles during vibration.These mesoscopic quantifications characterize the evolution of the skeleton structure,which bears the majority of the load in granular materials.During vibration,the results show that the evolution of force chains is consistent with the development and fluctuation of deviatoric stress.The variation scale of the skeleton structure is found to be proportional to the reduction in shear resistance of granular materials when subjected to high-frequency vibration.A larger scale of force chain network variation results in a greater reduction of normalized shear resistance.