Abstract

Foundation soil of offshore structures may be subjected to various non-proportional cyclic loadings, such as wave loading, tide loading and earthquake loading. The consolidation state may affect the undrained behaviour of clay under pure rotation of principal stress directions. A series of cyclic undrained torsional tests were performed on normally and over consolidated clay subjected to pure rotation of principal stress directions at constant deviatoric stress conditions. The effects of over consolidation ratio (OCR) on the excess pore water pressure, stress-strain loop, stiffness and non-coaxial behaviour of the clay were analyzed under different deviatoric stresses and intermediate principal stress coefficients (b values). The results indicate that owing to the pure principal stress rotation alone, strain and excess pore water pressure accumulated in samples and the accumulation is affected by OCRs, deviatoric stress amplitudes and b values. Negative excess pore water pressure and stress dilatancy can be observed in over consolidated clay. Compared with shear stiffness, the normal differential stiffness experiences greater degradation under the pure rotation of principal stress. The shear stiffness of over consolidated clay may show an increase with loading cycles, while the normal differential stiffness degrades at low deviatoric stress value. Over consolidated clay shows non-coaxial behaviour and the greater the OCR values or the smaller the deviatoric stress, the larger the non-coaxial angle. The effects of b values on the non-coaxial behaviour of over consolidated clay are also observed.

• HIGHLIGHTS

• Over-consolidated clay subjected to pure rotation of principal stress.

• The effects of OCR, deviatoric stress and b value were analyzed.

• Negative EPWP and stress dilatancy were observed in over consolidated clay.

• The greater the OCR, the larger the non-coaxial angle.

摘要

海上结构物的地基土可能承受各种非比例循环荷载，如波浪荷载、潮汐荷载、地震荷载等。固结状态可能会影响主应力方向纯旋转下粘土的不排水行为。对正常和超固结粘土进行了一系列循环不排水扭转试验，在恒定偏应力条件下进行主应力方向的纯旋转。分析了不同偏应力和中间主应力系数（b值）下超固结比（OCR）对粘土超孔隙水压力、应力应变环、刚度和非同轴行为的影响。结果表明，仅由于纯主应力旋转，样品中累积的应变和超孔隙水压力，累积量受 OCR、偏应力幅值和 b 值的影响。在超固结粘土中可以观察到负的超孔隙水压力和应力膨胀。与剪切刚度相比，法向微分刚度在主应力纯旋转下经历了更大的退化。超固结粘土的剪切刚度可能会随着加载周期的增加而增加，而法向微分刚度在低偏应力值下会降低。超固结粘土表现出非同轴行为，OCR 值越大或偏应力越小，非同轴角越大。还观察了 b 值对超固结粘土非同轴行为的影响。在超固结粘土中可以观察到负的超孔隙水压力和应力膨胀。与剪切刚度相比，法向微分刚度在主应力纯旋转下经历了更大的退化。超固结粘土的剪切刚度可能会随着加载周期的增加而增加，而法向微分刚度在低偏应力值下会降低。超固结粘土表现出非同轴行为，OCR 值越大或偏应力越小，非同轴角越大。还观察了 b 值对超固结粘土非同轴行为的影响。在超固结粘土中可以观察到负的超孔隙水压力和应力膨胀。与剪切刚度相比，法向微分刚度在主应力纯旋转下经历了更大的退化。超固结粘土的剪切刚度可能会随着加载周期的增加而增加，而法向微分刚度在低偏应力值下会降低。超固结粘土表现出非同轴行为，OCR 值越大或偏应力越小，非同轴角越大。还观察了 b 值对超固结粘土非同轴行为的影响。超固结粘土的剪切刚度可能会随着加载周期的增加而增加，而法向微分刚度在低偏应力值下会降低。超固结粘土表现出非同轴行为，OCR 值越大或偏应力越小，非同轴角越大。还观察了 b 值对超固结粘土非同轴行为的影响。超固结粘土的剪切刚度可能会随着加载周期的增加而增加，而法向微分刚度在低偏应力值下会降低。超固结粘土表现出非同轴行为，OCR 值越大或偏应力越小，非同轴角越大。还观察了 b 值对超固结粘土非同轴行为的影响。

• 强调

• 承受主应力纯旋转的超固结粘土。

• 分析了 OCR、偏应力和 b 值的影响。

• 在超固结粘土中观察到负 EPWP 和应力膨胀。

• OCR越大，非同轴角越大。