土石坝填料一般处于平面应变状态,目前填料力学特性研究基本采用大型三轴试验。由于三轴应力状态下中主应力等于小主应力,平面应变状态下大坝填料的力学性能会被低估。为充分认识填料潜能,科学设计和合理评估土石坝,有必要对填料开展平面应变试验研究。应用大型真三轴仪对填料进行了大型平面应变试验,共开展了4种不同初始干密度的粗粒土平面应变各向等压固结排水剪切试验。结果表明:应力-应变关系主要为应变硬化型,应力曲线呈爬升型,体变表现为剪缩。某一小主应力下,大小主应力之差的最大值随初始干密度的增大呈线性增大;初始干密度一定时,大小主应力之差的最大值与小主应力呈线性关系增大。初始剪切阶段,小主应力一定时,偏应力与球应力之比曲线斜率随初始干密度的增大而增大,随剪切变形的发展,不同初始干密度的应力比曲线逐渐趋于接近。偏应力随球应力的增大单调增加则对应应变硬化型,若偏应力随球应力的增大先增加后减小则对应应变软化型。相同小主应力时,初始弹性模量随初始干密度的增大而增大,近似呈线性关系;某一初始干密度下,初始弹性模量随小主应力的增大基本呈线性关系增大。中主应力系数随大主应力方向应变的增大而增大,曲线形态呈三折线形,初始剪切阶段增长较为缓慢,随剪切变形的增大增长相对加快并呈线性关系增大,如曲线末端下弯为应变硬化型,曲线末端上翘为应变软化型。

At present, large-scale triaxial tests are used to investigate the mechanical properties of the filling of earth-rockfill dams, which are generally under plane strain state. Because the intermediate principal stress is equal to the minor principal stress in triaxial stress state, the mechanical properties of the filling under plane strain state will be underestimated. To fully comprehend the potential of the fill material for scientific design and rational evaluation of earth-rockfill dams, it is necessary to conduct plane strain test of the filling material. Large-scale plane strain tests were performed on the filling material using a large-scale true triaxial apparatus. A series of plane strain isotropic consolidation and drainage shear tests were carried out on coarse-grained soils with four different initial dry densities. Test results indicate that the stress-strain relationship predominantly exhibits strain hardening, with a rising stress curve and shear shrinkage-induced volumetric changes. Under a given minor principal stress, the maximal difference between the major and minor principal stresses increases linearly with the initial dry density. Similarly, when the initial dry density remains constant, this difference also increases linearly with minor principal stress. During the initial shear stage, the slope of the stress ratio curve between deviatoric and spherical stresses rises with increasing initial dry density. As shear deformation progresses, the stress ratio curves for different initial dry densities converge. A monotonically increasing deviatoric stress with spherical stress denotes strain hardening, whereas a deviatoric stress that first rises and then falls indicates strain softening. The initial elastic modulus under the same minor principal stress rises linearly with the initial dry density. At a specific initial dry density, the initial modulus increases linearly with the minor principal stress. The intermediate principal stress coefficient grows with the strain in the major principal stress direction, forming a three-segment broken line curve. Initially, the growth is slow during shear stage, but it accelerates linearly with increasing shear deformation. A slightly downward-bent curve end correlates with strain hardening, while a slightly upward-bent end corresponds to strain softening.