基于多尺度研究方法的深基础建造及加载过程特性分析

发布时间：2018-06-01 05:03

本文选题：宏细观多尺度 + 沉井下沉　；参考：《东南大学》2015年硕士论文

【摘要】：随着计算机技术的发展,大量学者开始采用数值分析法对岩土工程问题进行模拟分析,并取得了大量成果。岩土工程中广泛采用有限差分法和离散元法两种数值分析方法,但两者都存在各自的缺点。国内外学者提出了通过两种方法耦合分析来弥补两种方法的缺点的设想,从此,离散-连续耦合分析方法成为了目前国内外学者的研究热点。本文提出了三维离散元-有限差分法耦合分析方法,并完成pFC3D和FLAC3D耦合计算程序。采用其计算程序对沉井下沉过程、沉桩过程、沉箱-垫层-桩复合基础加载过程进了宏细观多尺度耦合分析,主要的研究工作及结论如下：(1)提出了离散元-有限差分法耦合算法,通过模拟压缩试验、直剪试验、三轴试验三种室内试验,证明本文所提出的离散元-有限差分法耦合计算方法能够使耦合界面法向力和切向力准确地传递,并且保证在颗粒与差分网格的宏细观参数相互匹配的情况下,离散元和有限差分网格耦合建模能够保证本构关系相同,两者之间变形协调。(2)对沉井下沉过程进行数值模拟,探究沉井下沉过程机理。数值模拟结果表明,沉井下沉过程中,沉井侧壁土压力分布曲线有明显的拐点,在刃脚附近出现应力松弛区域,致使沉井侧壁土压力减小并逐渐趋于主动土压力,在刃脚附近侧壁土压力甚至小于主动土压力；采用“土拱效应”理论,对沉井侧壁土压力进行计算,计算结果更加接近实际情况。(3)对沉桩过程进行数值模拟,探究沉桩过程机理。数值模拟结果表明,沉桩尺寸对沉桩挤土效应影响很大,桩周土体位移随着桩径的增大而增大,且桩周土体位移沿远离桩轴方向迅速衰减；振动沉桩可以有效的减小桩体在沉桩过程中桩侧摩阻力以及桩端阻力,但并不是沉桩振动频率越高越好,其振动频率应该根据土体性质进行调整,以达到最佳振动频率。(4)对沉箱-垫层-桩复合基础加载过程进行数值模拟,分析了垫层厚度对沉箱-垫层-桩复合基础受力特性的影响。数值模拟结果表明,垫层厚度越大,基础沉降越大,桩顶刺入量越大,土体荷载分担比越高；在加载过程中,随着荷载的增大,土体荷载分担比逐渐下降,桩荷载分担比逐渐升高；其他条件相同情况下,桩顶刺入垫层程度与桩位置有关,内部基桩刺入量小,外部基桩刺入量相对较大。通过对三种基础形式的离散元-有限差分法耦合计算分析,较好地从宏细观多尺度分析了三种基础在建造或加载等过程的特性,验证了本文提出的离散元-有限差分法耦合计算的实用性。
[Abstract]:With the development of computer technology, a large number of scholars began to use numerical analysis method to simulate and analyze geotechnical engineering problems, and achieved a lot of results. Finite difference method and discrete element method are widely used in geotechnical engineering, but both have their own shortcomings. Scholars at home and abroad have put forward the idea of two methods coupling analysis to make up for the shortcomings of the two methods. Since then, the discrete-time continuous coupling analysis method has become the research hotspot of scholars at home and abroad. In this paper, the coupling analysis method of 3D discrete element-finite-difference method is presented, and the pFC3D and FLAC3D coupling calculation program is completed. The process of sinking, piling and loading of caisson cushion pile composite foundation are analyzed by using its calculation program. The main research work and conclusions are as follows: (1) the discrete element finite difference method (DFDM) coupling algorithm is proposed. The three indoor tests are simulated compression test, direct shear test and triaxial test. It is proved that the discrete element finite difference method presented in this paper can accurately transfer the normal and tangential forces at the coupled interface, and ensure that the particles and the meso-macro parameters of the difference mesh can match each other. The coupling modeling of discrete element and finite difference grid can guarantee the same constitutive relation. The deformation coordination between them can be used to simulate the sinking process of caisson and to explore the mechanism of sinking process of caisson. The numerical simulation results show that there is an obvious inflection point in the lateral wall earth pressure distribution curve of the caisson during the sinking process, and the stress relaxation area appears near the edge of the caisson, which results in the decrease of the side wall earth pressure of the caisson and gradually tends to the active earth pressure. The soil pressure of side wall near the edge foot is even smaller than that of active earth pressure, and the "soil arch effect" theory is used to calculate the lateral wall earth pressure of caisson, and the calculated results are closer to the actual situation. Explore the mechanism of piling process. The numerical simulation results show that the piling size has a great influence on the pile-squeezing effect, the soil displacement around the pile increases with the increase of the pile diameter, and the soil displacement around the pile decays rapidly along the direction away from the pile axis. Vibration piling can effectively reduce the pile side friction and pile tip resistance in the process of piling, but it is not that the higher the vibration frequency, the better, the vibration frequency should be adjusted according to the soil properties. The loading process of caisson-cushion-pile composite foundation is numerically simulated to reach the optimum vibration frequency. The influence of cushion thickness on the mechanical characteristics of caisson-cushion-pile composite foundation is analyzed. The numerical simulation results show that the greater the cushion thickness, the greater the foundation settlement, the greater the pile top impinging, the higher the load-sharing ratio of soil, and the lower the load-sharing ratio of soil is during the loading process with the increase of load. Under the same conditions, the degree of pile top penetration into the cushion is related to the pile position, the internal pile penetration is small, and the external pile penetration is relatively large. By means of the coupled calculation and analysis of three basic forms of discrete element and finite difference method, the characteristics of the three foundations in the process of construction or loading are well analyzed from the macro and mesoscale view. The practicability of the discrete-time finite-difference method proposed in this paper is verified.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU473

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