波浪作用下原状软粘土动力特性与微观结构关系试验研究

发布时间：2018-01-06 06:01

本文关键词：波浪作用下原状软粘土动力特性与微观结构关系试验研究　出处：《浙江大学》2013年硕士论文　论文类型：学位论文

【摘要】：随着海洋资源的开发与海洋空间的利用,在海床软土地基上修建了越来越多的海工建筑物,这些设施在建设和使用过程中长期受到波浪荷载的作用,与此同时,波浪荷载所引起的岩土工程问题受到了越来越多的关注。许多学者对波浪荷载下饱和粘土的动力特性做了大量的研究,但研究成果大多以动三轴试验为主,无法模拟波浪荷载下主应力轴连续循环旋转的复杂应力路径。另外,以往对于土体特性的研究多停留在宏观力学的角度上,对引起宏观动力反应的土体微观结构尚缺乏系统的研究,因此,要想全面了解复杂应力路径下的土体特性,就必须在宏观力性试验的基础上,系统深入地开展土体微观结构变形和破坏机理研究,揭示土体微观结构参数与宏观力学特性之间的关系。本文在以往研究的基础上,利用浙江大学5Hz空心圆柱扭剪仪,模拟波浪荷载下海床地基土体单元的实际受力条件,对饱和软粘土的动力特性进行研究,采用扫描电镜(SEM)和PCAS微观定量分析系统,对软土固结过程及循环加载前后的土体微观结构变化特征进行定性和定量研究,并分析宏观特性与微观结构变化之间的关系。本文主要工作和研究成果如下： (1)分别开展了不同循环应力比和不同频率下的主应力轴连续旋转循环剪切试验。试验结果表明：循环应力比和频率对循环荷载作用下土体的孔压特性、应变特性和动模量的衰减特性均有较大的影响。与动三轴试验结果相比,受主应力轴连续旋转的影响,土体孔压累积、应变发展及模量衰减速度均较快,试样破坏时孔压曲线没有明显的拐点也没有达到稳定状态,破坏所需的循环次数大幅减少,同样循环次数时土体软化程度更高,土体临界循环应力比由0.5减小到0.2左右,动强度降低了35%-40%。 (2)通过一维压缩固结试验对土体的压缩特性及其微观孔隙特征的变化规律进行研究,得到了微观结构特征参数随固结压力的变化规律,发现土体压缩性能的变化与微观结构参数的变化具有密切的相关性,揭示了土体受力变形的微观机理,进而达到研究和预测土体压缩变形的目的。 (3)对循环加载前后及试样破坏后剪切带内外土体微观结构进行研究,从微观层面上揭示了动荷载下的土体微观结构变形和破坏机理。循环剪应力作用下,孔隙破碎的同时兼并生长,这是剪切带上“褶皱”现象的微观本质,剪切带上多数孔隙排列方向与剪切带方向一致,不同试样破坏时的孔隙尺度及其分布规律相差不大对应宏观上的临界轴向破坏应变水平也基本一致。静荷载和动荷载下土体微观结构变形机理不同,动荷载下土体微观结构的变化比静力条件下复杂的多。循环应力比和频率对土体微观结构变化的影响存在差异,微观结构参数随循环应力比的变化有一定的规律性,随频率的变化规律性不明显。
[Abstract]:With the development of marine resources and the utilization of ocean space, more and more marine structures have been built on the soft soil foundation of the seabed. These facilities have been subjected to wave loads for a long time in the process of construction and use, at the same time. The geotechnical engineering problem caused by wave load has been paid more and more attention. Many scholars have done a lot of research on the dynamic characteristics of saturated clay under wave load, but the research results are mostly dynamic triaxial test. It is impossible to simulate the complex stress path of continuous cyclic rotation of principal stress axis under wave load. There is no systematic research on the microstructure of soil mass which causes the macroscopic dynamic response. Therefore, in order to fully understand the characteristics of soil under complex stress path, it is necessary to base on the macroscopic force test. In order to reveal the relationship between soil microstructure parameters and macroscopic mechanical properties, the deformation and failure mechanism of soil microstructure is studied. On the basis of previous research, the dynamic characteristics of saturated soft clay are studied by using the 5 Hz hollow cylindrical torsional shear apparatus of Zhejiang University to simulate the actual stress conditions of the soil element in the sea bed under the wave load. The microstructure of soft soil before and after cyclic loading was studied qualitatively and quantitatively by means of scanning electron microscope (SEM) and PCAS microquantitative analysis system. The main work and results of this paper are as follows: 1) continuous rotating cyclic shear tests of principal stress axis were carried out under different cyclic stress ratios and different frequencies. The experimental results show that the cyclic stress ratio and frequency affect the pore pressure characteristics of soil under cyclic load. Compared with the dynamic triaxial test results, the pore pressure accumulation, strain development and modulus decay rate of soil are faster due to the continuous rotation of the principal stress axis. The pore pressure curve has no obvious inflection point and does not reach a stable state when the specimen is destroyed, and the number of cycles required for failure is greatly reduced, and the softening degree of soil is higher when the same number of cycles occurs. The critical cyclic stress ratio decreases from 0.5 to 0.2 and the dynamic strength decreases from 35 to 40. 2) through one-dimensional compression consolidation test, the variation law of soil compression characteristics and micro-pore characteristics is studied, and the variation law of microstructure characteristic parameters with consolidation pressure is obtained. It is found that the variation of soil compression performance is closely related to the change of microstructure parameters, and the microscopic mechanism of soil deformation is revealed, and the purpose of studying and predicting soil compression deformation is achieved. 3) the microstructure of soil in and out of the shear band before and after cyclic loading is studied, and the mechanism of deformation and failure of soil under dynamic loading is revealed from the micro level, under cyclic shear stress. The microcosmic essence of the "fold" phenomenon in the shear zone is that the pores are broken and grow simultaneously, and most of the pores in the shear zone are arranged in the same direction as the shear zone. The pore size and distribution of different specimens are similar to the macroscopic critical axial failure strain level. The deformation mechanism of soil microstructure is different under static load and dynamic load. The variation of soil microstructure under dynamic load is more complex than that under static condition. The influence of cyclic stress ratio and frequency on the change of soil microstructure is different. The variation of microstructure parameters with cyclic stress ratio is regular, but the variation with frequency is not obvious.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU442;TU447

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