Abstract To investigate the effect of the vertical effective and initial static shear stresses on cyclic resistance under cyclic loading with principal stress rotation, a series of cyclic direct simple shear tests were conducted on loose and dense Nakdong River sands. The results revealed that the increasing vertical effective stress (σ′v0) often decreased the cyclic resistance, and the decrease was more evident for a high initial static shear ratio (α = 0.2). The degree of reduction of the correction factor Kσ predicted by recommended methods in practice mostly showed more conservative results than the measured Kσ values in this study. Increasing the initial static shear stress decreased the cyclic resistance of the loose sand. For the dense sand, the cyclic resistance either increased or decreased, depending on the combined effect of the σ′v0 and α levels. The correction factor Kα decreased minimally to 0.689 for the loose sand and rose maximally to 1.175 for the dense sand. When the relative density (Dr) increased from 40% to 80%, the increase in the cyclic resistance for a high α (=0.2) was considerably greater than that for α = 0. The cyclic response of the loose sand was due to sudden flow deformation without any apparent shear strain accumulation, regardless of the α value; while the cyclic response of the dense sand indicated plastic strain accumulation. Thus, the cyclic resistance of sand is influenced by the combined effect of Dr, σ′v0, and α, with the potential influence of principal stress rotation.

中文翻译：

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循环直接简单剪切试验中垂直有效剪应力和初始静剪应力对砂土液化阻力的影响

摘要 为了研究竖向有效剪应力和初始静剪应力对主应力旋转循环荷载作用下循环阻力的影响，对松散密实的洛东河沙进行了一系列循环直接简单剪切试验。结果表明，竖向有效应力（σ'v0）的增加往往会降低循环阻力，并且对于高初始静剪切比（α = 0.2）降低更为明显。实践中推荐的方法预测的修正因子Kσ的降低程度，大多显示出比本研究中实测的Kσ值更保守的结果。增加初始静剪应力会降低松散砂土的循环阻力。对于密砂，循环阻力要么增加，要么减少，取决于 σ'v0 和 α 水平的综合影响。对于松散的沙子，修正系数 Kα 最小地下降到 0.689，对于密实的沙子，最大地上升到 1.175。当相对密度 (Dr) 从 40% 增加到 80% 时，高 α (=0.2) 的循环阻力增加明显大于 α = 0 时的循环阻力。流动变形没有任何明显的剪切应变积累，无论 α 值如何；而密砂的循环响应表明塑性应变积累。因此，砂土的循环阻力受 Dr、σ′v0 和 α 的综合影响，并具有主应力旋转的潜在影响。当相对密度 (Dr) 从 40% 增加到 80% 时，高 α (=0.2) 的循环阻力增加明显大于 α = 0 时的循环阻力。流动变形没有任何明显的剪切应变积累，无论 α 值如何；而密砂的循环响应表明塑性应变积累。因此，砂土的循环阻力受 Dr、σ′v0 和 α 的综合影响，并具有主应力旋转的潜在影响。当相对密度 (Dr) 从 40% 增加到 80% 时，高 α (=0.2) 的循环阻力增加明显大于 α = 0 时的循环阻力。流动变形没有任何明显的剪切应变积累，无论 α 值如何；而密砂的循环响应表明塑性应变积累。因此，砂土的循环阻力受 Dr、σ′v0 和 α 的综合影响，并具有主应力旋转的潜在影响。而密砂的循环响应表明塑性应变积累。因此，砂土的循环阻力受 Dr、σ′v0 和 α 的综合影响，并具有主应力旋转的潜在影响。而密砂的循环响应表明塑性应变积累。因此，砂土的循环阻力受 Dr、σ′v0 和 α 的综合影响，并具有主应力旋转的潜在影响。