小主应力方向加载条件下的掺砾黏土真三轴试验

对土石坝心墙掺砾黏土开展模拟心墙单元小主应力方向加载的真三轴试验，首先对试样进行不同围压条件下等向固结，然后保持小主应力恒定，通过调整大主应力和中主应力，以模拟土石坝竣工后的初始三向应力状态。试验过程中保持大主应力和中主应力恒定，从小主应力方向单向加载，以模拟土石坝蓄水过程中心墙单元所经历的应力路径。试验结果与常规三轴试验以及复杂应力条件下大主应力方向真三轴加载试验结果都有显著不同。不同初始应力条件下，不同主应力方向的初始切线模量和初始切线泊松比的变化规律非常复杂，应力–应变显现出明显的各向异性。在心墙堆石坝施工过程及蓄水过程中，心墙单元所经历的应力路径明显不同，合理的土体本构模型应该对这种由于加荷路径不同所引起的不同方向模量和泊松比进行合理描述。

True triaxial test on clay mixed with gravel with stress increment loading from minor principal stress direction

True triaxial tests on clay mixed with gravel were carried out under complex stress state to simulate the loading process of core wall elements under water storage process, and loading was applied from the minor principal stress direction. Under initial state, the major principal stress and the second principal stress were adjusted with constant minor principal stress; initial anisotropic stress state was reached to simulate the stress state of dam elements. The major principal stress and second principal stress were then kept constant. Minor principal stress increment was applied to simulate the stress path that core wall elements go through during the process of water storage. Test results show significant differences compared with the result of conventional triaxial tests and true triaxial tests loading from major principal stress direction. Under different initial stress conditions, the initial tangent modulus and initial Poisson’s ratio of the principal stress direction are very complex, and the stress - strain curve shows obvious anisotropy. In the process of core wall rockfill dam construction and the water storage process, the stress path experienced by the core wall unit is obviously different. The reasonable soil constitutive model should be used to describe the modulus and Poisson’s ratios caused by the different loading paths.