This paper presents the findings from an experimental study focusing on the undrained cyclic behavior of sand in the presence of initial static shear stress. A series of undrained cyclic torsional shear tests was performed on saturated air-pluviated Toyoura sand specimens up to single amplitude shear strain ($\gamma$_SA) exceeding 50%. Two types of cyclic loading conditions, namely, stress reversal (SR) and stress non-reversal (SNR), were employed by changing the amplitude of the combined initial static shear and cyclic shear stresses. The tests covered a broad range of initial states in terms of relative density (Dr = 20–74%) and the initial static shear stress ratio (α = 0–0.30). The following five distinct modes of deformation were identified from the tests based on the density state, the transient undrained peak shear stress, and the combined cyclic and static shear stresses: 1) static liquefaction, 2) cyclic liquefaction, 3) cyclic mobility, 4) shear deformation failure, and 5) limited deformation. Of these, cyclic liquefaction and static liquefaction are the most critical. They occur in very loose sand (D_r ≤ 24%) under SR and SNR, respectively, and are characterized by abrupt flow-type shear deformation. Cyclic mobility occurs under SR in loose to dense sand with D_r ≥ 24%. Contrarily, shear deformation failure typically occurs under SNR in sand with 24 < D_r < 65%, and limited deformation may take place in dense sand with D_r ≥ 65%. In this paper, a stress-void ratio-based predictive method is proposed to identify the likely mode of deformation/failure in sand under undrained shear loading with static shear. Furthermore, the cyclic resistance is evaluated at three different levels of $\gamma$_SA (i.e., small, $\gamma$_SA = 3%; moderate, $\gamma$_SA = 7.5%; and large, $\gamma$_SA = 20%). The results show that, independent of the density state, the cyclic resistance continuously decreases with an increase in α at the small $\gamma$_SA level, while it first decreases and then increases for both loose and dense sand at the moderate and large $\gamma$_SA levels.

本文介绍了一项实验研究的结果，该研究侧重于在初始静态剪应力存在下砂的不排水循环行为。对饱和空气雨淋 Toyoura 砂试样进行了一系列不排水循环扭转剪切试验，试验达到单幅剪切应变（$\gamma$_SA ) 超过 50%。通过改变初始静态剪切和循环剪切应力组合的振幅，采用两种类型的循环加载条件，即应力反转 (SR) 和应力非反转 (SNR)。测试涵盖了相对密度 ( D r = 20–74%) 和初始静态剪切应力比 (α = 0–0.30)方面的广泛初始状态。根据密度状态、瞬态不排水峰值剪切应力以及循环和静态剪切应力的组合，从测试中确定了以下五种不同的变形模式：1) 静态液化，2) 循环液化，3) 循环流动性，4 ) 剪切变形破坏，和 5) 有限变形。其中，循环液化和静态液化最为关键。它们出现在非常松散的沙子中（D _r  ≤ 24%) 分别在 SR 和 SNR 下，并以突然流动型剪切变形为特征。循环流动在 SR 下发生在松散到致密的沙子中，D _r  ≥ 24%。相反，剪切变形破坏通常在 SNR 下发生在 24 <  D _r  < 65% 的砂中，而在D _r  ≥ 65% 的致密砂中可能发生有限变形。在本文中，提出了一种基于应力空隙比的预测方法，以识别砂在不排水剪切载荷和静态剪切下可能的变形/破坏模式。此外，循环阻力在三个不同的水平上进行评估$\gamma$_SA（即小，$\gamma$_SA  = 3%；缓和，$\gamma$_SA  = 7.5%；和大，$\gamma$_SA  = 20%）。结果表明，与密度状态无关，循环电阻随着 α 的增加而持续降低。$\gamma$_SA水平，而在中等和大的松散和密实砂土中先减小后增大$\gamma$_SA级别。