基于大型真三轴试验的砂砾石料强度–剪胀特性研究

Strength and dilation of sandy gravel material based on large-scale true triaxial tests

为了揭示中主应力系数和应力水平对苏洼龙水电站坝基覆盖层砂砾石料的强度与变形特性的影响规律,结合一种微摩阻加载技术,开展一系列大型真三轴试验。在广义应力框架内讨论该砂砾石料的应力、强度和剪胀问题。结果表明:首先,对于该砂砾石料,内摩擦角随中主应力系数增加而增大,随应力水平提高而减小。3个经典强度理论中,Lade-Duncan准则的预测结果与试验结果更为相符,但当b值较大时,预测结果仍偏低估计了实际的内摩擦角;其次,随着中主应力系数b值增加,应力路径的斜率变缓,同时所达到的峰值强度提高,但峰值强度对应的q/p(q,p分别为广义偏应力和平均主应力)应力比越小,表明在单位平均主应力水平下所能发挥的最大强度减小。总体而言,剪胀角随应力水平增加而减小,亦随b增加而减小。

To reveal the strength and deformation characteristics of sandy gravel material covering the dam foundation in Suwalong hydropower station affected by the intermediate principal stress ratio and the stress level,a series of large-scale true triaxial tests were performed,combined with a special friction-reduction technique. The stress,strength and dilation were then analyzed under the framework of generalized deviatoric stress and mean effective stress. The internal friction angle was found to increase with the rising of intermediate principal stress ratio,but decrease with the stress level. Among three classical strength criteria,Lade-Duncan criterion shows the best fitting to the tested results,despite of the underestimation at higher level of b values. With the increasing of b value,the slope of the stress path reduces. Meanwhile,the peak strength increases with the decreasing of the stress ratio q/p（q is deviatoric stress,p is mean effective stress）,indicating that the mobilized strength reduces at unit mean effective stress. The angle of dilation decreases with the increasing of stress level and intermediate principal stress.