Undrained Dynamic Strength Behavior of Saturated Nanjing Fine Sand under Wave Load

Cyclic vertical-torsional coupling tests were performed on saturated Nanjing fine sand with a relative density of 50% using a hollow cylinder apparatus. The effect of complex initial stress conditions on undrained dynamic strength of saturated Nanjing fine sand was investigated. It is shown that the initial confining pressure, p₀, the initial stress ratio, R₀, and the initial angle of maximum principal stress direction, α₀, have great effects on the characteristics of the dynamic strength of Nanjing fine sand. The dynamic strength increases with p₀ and R₀, while it decreases with α₀. The effect of initial intermediate principal stress parameter b₀ on the dynamic strength is slight.     

黄河水下三角洲海底斜坡波致稳定性分析

以 Iversion的海底稳定渗流理论为基础 ,运用静力极限平衡方法和库仑破坏准则 ,提出了以海底水下斜坡坡度、沉积物有效内摩擦角和内聚力为自变量 ,波浪在海底产生的孔压梯度为参变量的海底稳定性分析方法。并给出了黄河水下三角洲不同土质所需的临界孔压梯度判断曲线 ,预测了黄河水下三角洲的海底稳定性 ,其分析结果与实测资料吻合良好     

Effect of Band Width on Fatigue Life under Random Stress Response

A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.     

Calculation of Wave Radiation Stress in Combination with Parabolic Mild Slope Equation

A new method for the calculation of wave radiation stress is proposed by linking the expres-sions for wave radiation stress with the variables in the parabolic mild slope equation.The governing equa-tions are solved numerically by the finite difference method.Numerical results show that the new methodis accurate enough,can be efficiently solved with little programming effort,and can be applied to the calcu-lation of wave radiation stress for large coastal areas.     

Stiffness Degradation of Undisturbed Saturated Soft Clay in Yangtze Estuary under Complex Stress Conditions

Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on saturated soft marine clay in the Yangtze estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotorpic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared to the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does. Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.     

南黄海辐射沙洲区悬沙潮扩散规律数值研究

在对南黄海辐射沙洲区的潮汐、潮流特征作进一步探讨的基础上,数值模拟了该区的悬沙潮扩散。根据计算结果,分析了计算海域悬沙含量在一个半日潮过程中随潮流场的瞬时变化规律,研究了不同地点悬沙含量与潮位、潮流的关系,总结了涨、落潮平均含沙量的平面分布规律。结果表明,该区的潮流场控制着悬沙的扩散、运移和分布,进而控制着海底地形的发育,尤其是辐射沙洲北大南小不对称格架的塑造与辐射沙洲根部的加积淤高。