粒状土直剪试验的二维离散元模拟

发布时间：2018-10-19 12:37

【摘要】：直剪试验具有诸多优点,长期以来作为粗粒土主要的试验方法之一来获得较为可靠的土体抗剪强度。然而其固有的缺陷和局限性也不容忽视。因此,通过颗粒流数值模拟方法从微观颗粒的角度来认识土体颗粒本身在剪切过程中的受力与变形的情况,进而优化其试验结果,极具实际意义。本文首先总结国内外关于直剪试验的颗粒流模拟、以及直剪试验的特点,从而分析了颗粒流数值模拟的基本原理和方法,建立了普通直剪试验和大型直剪试验的二维离散元模型。其次,标定了模型试验的细观输入参数,得到了细观输入参数对试验宏观性质的影响,进而对室内试验进行了仿真对比,估算了粒状土直剪试验的应变。最后基于直剪试验缺陷探讨,提出了三种优化方法。得到了以下结论： (1)借助PFC2D颗粒流方法,可以较准确地模拟粒状土的直剪试验过程,进而对直剪试验的缺陷进行微观机理的分析,试验结果可信,试验成本非常低。 (2)通过颗粒流模拟的粒子位移场监测,得到直剪试验的剪切带宽度范围,接近较早之前的研究结论,进而估算了粒状土体材料的整体正应变和剪应变。 (3)模拟结果表明使用反向加载机构可以考虑侧壁摩擦力对于正应力的影响；侧壁摩擦力与竖向位移-剪位移关系曲线较为吻合。对比室内试验与修正的结果表明,剪切盒侧壁的摩擦力对于强度参数的影响并不十分明显。 (4)利用颗粒流模拟粒状土剪切运动的规律并结合应力分析提出了剪切面偏转修正的数学公式,修正结果表明其影响不应当忽略。这不同于剪切面积改变的影响,剪切面积改变对强度影响不大,可以接受。 (5)从剪切面积改变和剪切面偏转的修正结果来看,非标直剪试验的试验结果并非差于标准试验(直径0.0618m)。
[Abstract]:Direct shear test has many advantages. As one of the main test methods of coarse grained soil for a long time, the shear strength of soil is relatively reliable. However, its inherent defects and limitations should not be ignored. Therefore, it is of great practical significance to understand the stress and deformation of soil particles in shear process from the point of view of microscopic particles by means of numerical simulation of particle flow, and then optimize the test results. This paper first summarizes the particle flow simulation and the characteristics of the direct shear test at home and abroad, and then analyzes the basic principles and methods of numerical simulation of particle flow. A two-dimensional discrete element model for general direct shear test and large-scale direct shear test is established. Secondly, the mesoscopic input parameters of the model test are calibrated, and the influence of the mesoscopic input parameters on the macroscopic properties of the test is obtained, and the strain of the granular soil direct shear test is estimated by the simulation and comparison of the indoor test. Finally, three optimization methods are proposed based on the discussion of the defect of direct shear test. The conclusions are as follows: (1) with the aid of PFC2D particle flow method, the direct shear test process of granular soil can be simulated more accurately, and the microcosmic mechanism of the direct shear test can be analyzed. The experimental results are reliable. The test cost is very low. (2) through particle displacement field monitoring simulated by particle flow, the shear band width range of direct shear test is obtained, which is close to the previous research conclusion. Furthermore, the global positive strain and shear strain of granular soil are estimated. (3) the simulation results show that the influence of lateral friction on normal stress can be considered by using reverse loading mechanism. The frictional force of lateral wall is in good agreement with the curve of vertical displacement-shear displacement. The results of laboratory test and correction show that, The influence of friction on the strength parameters of shear box is not obvious. (4) the mathematical formula of shear plane deflection correction is proposed by using particle flow to simulate the shear motion of granular soil and combining with stress analysis. The result shows that the effect should not be ignored. This is different from the effect of shear area change. Shear area change has little effect on strength and is acceptable. (5) from the correction results of shear area change and shear plane deflection, The results of non-standard direct shear test are not worse than that of standard test (diameter 0.0618m).
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU41

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