球应力循环条件下堆石料变形特性的试验研究

库水位反复升降过程中堆石体的应力状态表现为偏应力基本恒定、球应力往复循环变化，为探求球应力循环条件下堆石料的变形规律，以取自现场的堆石材料为研究对象，通过控制孔隙水压力来实现球应力增大–减小的低速循环应力路径静力三轴试验。研究结果表明：偏应力恒定、球应力循环条件下，体应变随球应力的减小而增大，随球应力增大而减小，总体表现出随循环周次向体积收缩发展的变化规律，循环周次对累积体应变的影响较小；剪应变的发展受应力条件的影响较为显著，有效球应力减小时或增幅较缓，或在第1循环周次内突增，有效球应力增加时，剪应变增幅较缓；累积剪应变与初始应力比和试验过程中的动态应力比有关；土样可能存在类似临界状态线且处于其下方的“转折状态线”，当土样应力变化状态处于“转折状态线”与临界状态线之间的区域内时，土样状态将产生显著变化。

Experimental study on deformation characteristics of rockfill materials under cyclic loading of spherical stress

During periodic rise and fall in reservoir water level, the state of rockfill materials shows a basically constant deviatoric stress and a cyclic change in spherical stress. To investigate the deformation characteristics of rockfill materials under cyclic loading of spherical stress, a series of triaxial tests under the stress path of low-speed cyclic variations in spherical stress are conducted in this study by increasing or decreasing this stress through controlling pore water pressure. Results show that volumetric strain is increased with the decreasing spherical stress, and decreased with the increasing spherical stress. Generally, with cyclic times increasing, the materials show a trend of volume shrinkage, but the cumulative volumetric strain changes little. The development in shear strain is significantly affected by stress conditions. Effective shear strain increases slowly or increases suddenly in the first cycle times when spherical stress is reduced, while it increases slowly when effective spherical stress is increased. Cumulative shear strain is related to the initial stress ratio and the dynamic stress ratio during the test. The materials may likely have a “state-turning line” that is similar to the critical state line and falls below it. The state of a material will change significantly when its stress lies in the zone between this “state-turning line” and the critical state line.