【作者】 金丹；

【导师】 栾茂田；

【作者基本信息】 大连理工大学 ， 岩土工程， 2009， 博士

【摘要】 土的力学行为与加载路径密切相关。与单向剪切相比,多向剪切会产生额外的塑性体积应变,在不排水条件下孔隙水压力增长的速率较高,特别是在具有主应力轴连续旋转特点的加载条件下,砂土抵抗液化的能力也将更低。主应力方向旋转变化是地震、波浪等荷载作用下地基土体所受应力路径的主要特征,但目前这方面的研究成果还较少,且在已有研究资料中,几乎所有试验都为圆形应力路径试验,对于更一般情况的椭圆形应力路径试验,则几乎没有相关研究资料。因此有必要对此种复杂应力条件下土的力学行为进行研究。另外,实际中海床的初始应力状态往往是各向异性的,作为海床与海洋建筑物地基稳定性评价中的一个基本而重要问题,探讨砂土的变形与强度特性时必须考虑各向非均等的复杂初始应力状态和复杂的循环应力变化模式。因此,本文结合国家自然科学基金重点项目“海洋土的工程特性及其地基的变形机理研究”(NO.50639010)和国家自然科学基金项目“复杂应力状态下土的本构模型及其在海床动力学中的应用”(NO.50179006),利用先进的“土工静力—动力液压三轴—扭转多功能剪切仪”,针对饱和砂土开展了考虑主应力方向旋转变化的系列椭圆应力路径试验研究。主要研究内容和研究成果如下:1.进行了大量主应力轴连续旋转条件下的椭圆应力路径试验,探讨了不同椭圆应力条件下饱和砂土的变形与强度特性,其结果填补了以往仅进行圆形应力路径试验研究的不足。结果表明,与弹性解基础上得到的偏应力保持不变的圆形应力路径相比,椭圆应力路径条件下的饱和砂土动强度发生较大范围的变化,所得到的变形性质也更为复杂。2.通过专门设计的对比试验,系统地研究了主应力方向旋转试验中竖向偏差应力与剪应力幅值之比对饱和砂土动强度的影响。研究表明:当保证椭圆面积不变时,土样会在竖向偏差应力与剪应力的幅值之比达到某一临界值时表现出最高的强度,应力幅值之比偏离此临界值越远,土样强度越低。初始主应力方向角、固结偏应力比与初始中主应力系数对此临界值均存在影响,文中给出了相应的取值范围。3.研究了复杂初始应力状态下饱和砂土的动强度特性。研究表明:初始主应力方向角与固结偏应力比对饱和砂土的动强度影响显著,而初始中主应力系数的影响不大。文中给出了饱和砂土动强度随各因素变化的参考幅度。4.研究了复杂初始应力状态下饱和砂土的动应变特性,分析初始主应力方向角、固结偏应力比、初始中主应力系数以及动应力幅值等因素对饱和砂土的动应变发展的影响。研究表明:非均等固结条件下,固结偏应力比对广义剪应变增长模式影响最为显著;初始主应力方向角对饱和砂土应力-应变关系特性影响最大。通过对大量试验数据的回归分析,得到一个可以描述不同固结偏应力比条件下累积广义剪应变随振次增长趋势的统一公式。5.分析孔隙水压力发展的时程曲线,研究饱和砂土的动孔隙水压力增长特性,分析各种因素对动孔隙水压力增长特性的影响。研究表明:非均等固结条件下,固结偏应力比对归一化后的孔隙水压力随振次增长模式影响最为显著;不同固结条件下的归一化孔隙水压力随应变增长模式却基本相同。建立了复杂应力条件下饱和砂土孔隙水压力的发展模式。更多还原

【Abstract】 Mechanical behavior of soil is closely associated with the loading patterns. Test results have shown that larger plastic volumetric strain as well as higher growth rate of pore water pressure would be generated in multi-directional shearing than in a single-directional one. Lower resistance of sand to liquefaction was also observed under the rotation of principal stress orientation. Principal stress rotation is the typical stress path when seismic or wave load is applied on the soil. But the study in this aspect is less, and almost all the existing research data is about circular path. It has been hardly studied for more general condition of oval path. Moreover, initial stress condition has significant influence on the dynamic behavior of sand. As a basic and important issue in the evaluation of the stability of seabed and ocean engineering structures, the complex initial anisotropic stress state as well as the complex variation pattern of cyclic stress must be taken into consideration in studying the deformation and strength properties of sands. For this sake, plenty of shear tests under oval paths were designed and performed on Fujian Standard Sand using the soil static and dynamic universal triaxial and torsional shear apparatus. The present research is supported by the National Natural Science Foundation Key Project of Study on Engineering Properties of Marine Soil and Deformation Mechanism of the Foundation (No. 50639010) and the National Natural Science Foundation Project of Study on Constitutive Model of Soil under the Complex Stress Condition and its Application in Seabed Dynamics (No. 50179006). Experimental study on rotation of principal stress orientation was focused on. The main content of the current research are as follows:1. Plenty of bidirectional shear tests under oval paths were designed and performed to research the deformation and strength characteristics of saturated sand. The research can remedy the deficiency of previous study on circular path only. The results show that, when compared to the results of circular paths tests, the dynamic intensity of sand gained in oval paths tests changes in a wide range, and the deformation properties are more complicated.2. The effect of magnitude ratio of normal stress difference and shear stress on dynamic resistance of saturated sand has been researched by special designed contrast tests. The results show that, when the bounding area of oval paths is kept constant, a critical value of the stress magnitude ratio could be found, under which the highest resistance of specimen is observed. The more the stress ratio deviates from the critical value, the lower intensity of sand is behaved. Initial orientation of the major principal stress, consolidated deviator stress ratio, and initial coefficient of intermediate principal stress all have effects on the critical value. The corresponding critical value range is given in chapter 3.3. Dynamic strength characteristics of saturated sand under complex initial stress condition have been researched. The results show that, the dynamic strength of sand is strongly depended on initial orientation of the major principal stress and consolidated deviator stress ratio, but less associated with initial coefficient of intermediate principal stress. The reference variation range of resistance of sand changing with the influence factors is given.4. Dynamic strain response of saturated sand under complex initial stress condition has been researched. Factors influence the development of dynamic strain are analyzed such as initial orientation of the major principal stress, consolidated deviator stress ratio, initial coefficient of intermediate principal stress and amplitude of cyclic stresses. A unified development model of dynamic strain for different consolidated deviator stress ratio has been put forward.5. The development characteristic of dynamic pore water pressure is investigated by analyzing the time-history curve of pore water pressure and considering various influence factors. The results show that, consolidated deviator stress ratio has the most significant effect on normalized pore water pressure developed with number of cycles. And the normalized pore water pressure developed with generalized shear strain is independent of various initial stress condition. Then the development model of residual pore water pressure with cyclic numbers and generalized shear strain are both established.更多还原