应力状态对粗粒料力学特性影响的大型真三轴试验

土石坝所处的应力状态较接近平面应变应力状态或三维应力状态，而常规三轴试验低估了粗粒料的力学性能。应用大型真三轴仪对常规三轴应力状态、平面应变应力状态和真三轴应力状态（ 0.25， 为中主应力系数， 、 、 分别为大、中、小主应力）下粗粒料的力学特性进行了压缩试验研究。试验结果表明：相同小主应力下，常规三轴试验、平面应变试验、真三轴试验的大、小主应力之差与大主应力方向应变的关系曲线依次变高变陡。某一试验加载条件下，体应变随球应力的增大而增大，初始剪切阶段增加较慢，随后呈线性增大，不同小主应力的体应变曲线较为接近。平面应变试验强度和真三轴试验强度比常规三轴试验强度有较大增长，真三轴试验强度增加百分比大于平面应变试验强度增加百分比。初始弹性模量随小主应力的增大呈线性增大。平面应变状态下中主应力系数随大主应力方向应变的增大而增大，初始剪切阶段增长较缓，之后近似呈线性增大。相同小主应力下，从常规三轴应力状态至平面应变应力状态再到真三轴应力状态，小主应力方向应变均为膨胀变形，且膨胀变形依次增大。同一试验加载条件下，小主应力较小时，应力比（偏应力与球应力之比）与偏应变的关系曲线位于上方。

Effects of stress state on mechanical properties of coarse granular material using large-scale true triaxial tests

The stress state of earth and rockfill dams is close to plane strain stress state or three-dimensional stress state, while the conventional triaxial test underestimates the mechanical properties of coarse granular material. The mechanical properties of coarse granular material under conventional triaxial stress state, plane strain stress state and true triaxial stress state( 0.25) were investigated by compression tests using large-scale true triaxial apparatus. The test results show that the relationship curves between the difference of major principal stress and minor principal stress and the strain in the direction of major principal stress become higher and steeper in sequence from conventional triaxial test, to plane strain test, to true triaxial test under the same minor principal stress. The volumetric strain increases with the increase of the spherical stress under a certain test loading condition, which shows a slow increase at the initial shearing stage and then increases linearly. The volumetric strain curves are close for different minor principal stresses. The strengths of plane strain stress state and true triaxial stress state are much greater than that of conventional triaxial stress state, and the percentage of strength increase under true triaxial stress state is larger than that of plane strain stress state. The initial elastic modulus increases linearly with the increase of the minor principal stress. In plane strain stress state, the coefficient of intermediate principal stress increases with the increase of the strain in the direction of major principal stress. The coefficient of intermediate principal stress increases slowly in the initial shearing stage and then increases linearly with the increase of the strain in the direction of major principle stress. From conventional triaxial stress state to plane strain stress state and then to true triaxial stress state, the strains in the direction of minor principal stress are all expansion deformations, and the expansion deformations increase successively under the same minor principal stress. The relationship curve between the ratio of deviatoric stress to spherical stress and deviatoric strain of small minor principal stress is located at the top for a certain test loading condition.