颗粒材料的级配相关临界状态力学特性模拟

发布时间：2018-01-09 13:15

本文关键词：颗粒材料的级配相关临界状态力学特性模拟　出处：《上海交通大学》2014年博士论文　论文类型：学位论文

【摘要】：岩土工程中颗粒材料的级配变动会在很大程度上影响材料在临界状态下的承载能力,可能引发结构物的大变形甚至导致整体失稳。因此,研究颗粒级配变动对材料临界状态特性的影响很有必要。通过室内实验结合数值试验,研究了不同初始级配对颗粒材料临界状态力学特性的影响;建立颗粒级配与材料临界状态的关系,并将其引进弹塑性本构模型,模拟颗粒级配变化引起的力学问题。(1)综合大量室内实验,研究了玻璃球和Hostun砂随颗粒级配变化的力学特性,得出临界状态与颗粒级配的关系。结果表明相同初始密实度材料的不排水剪切强度和相变偏应力比随着材料不均匀系数Cu的增加而降低,并在Cu达到10以后趋于稳定。通过二阶功分析指出颗粒级配对颗粒材料的不稳定性有很大影响,随着Cu的提高材料的静态液化潜能提高,变得更加不稳定。试验总结出颗粒材料临界状态参数随颗粒级配指标Cu变化的非线性规律。在e-p'平面上临界状态线的位置和斜率随着颗粒级配的拓宽而降低,在Cu达到10以后两者皆趋于稳定。在q-p'平面上颗粒材料的临界状态线则是一条直线,不受级配的影响。(2)数值试验拓展分析了多个应力路径下颗粒材料级配相关的力学响应。分析结果表明在相同加载条件下,材料的剪胀性随着颗粒级配的拓宽而下降,出现从剪胀到剪缩的转变;材料的不排水抗剪强度随着级配的拓宽而下降。试验结果进一步确认了临界状态参数与颗粒级配指标cu的非线性关系,不受排水条件和拉压剪切模式的影响。在e-p'平面上的临界状态线是唯一的,并随着级配的拓宽而下移;q-p'平面上的临界状态线则为直线,与级配无关。(3)基于细观力学分析,证明了颗粒材料临界状态线在e-p'平面上随颗粒级配移动以及在q-p'平面上呈直线且与级配无关的内在机理。由平均配位数的演变规律表明,颗粒材料在不排水剪切状态下较之排水剪切具有更高的不稳定性。在临界状态下平均配位数与平均有效应力的关系是唯一的,并随颗粒级配的拓宽而下移。应力-组构-接触力分析显示,临界状态下颗粒材料的各个细观组构各向异性分量对细观应力比的贡献程度相同,且与围压和级配无关,从而证实了在q-p'平面上颗粒材料的临界状态线呈直线,且与级配无关。(4)通过引入颗粒级配指标与临界状态的非线性关系,建立了颗粒材料的级配相关弹塑性本构模型。该模型可以描述任意颗粒级配材料的排水和不排水力学响应。与已有考虑级配效应的本构模型进行对比,指出不同模型预测效果差异的主要原因是临界状态参数与级配指标的关系不同。通过数值试验得出现有级配指标(cu和ig)都无法准确地描述颗粒材料级配相关的力学性能。提出了一个综合cu和ig优点的级配新指标igu并将其用于改进本构模型。模拟验证表明改进的本构模型能够更好地模拟任意级配颗粒材料的力学特性。(5)对本构模型进行有限元二次开发,用于分析可破碎地基土上浅基础的承载力问题。将本构模型编译成umat子程序,通过abaqus模拟浅基础的承载力问题。分析结果得出颗粒破碎引起了地基承载力的降低;随着地基土初始颗粒级配的拓宽,基础下压引起的颗粒破碎逐渐减弱,承载力下降趋势减弱。综上,本文的研究成果可为砂性土的本构研究、细观力学分析等提供借鉴,给颗粒级配变化引起的岩土工程问题提供有益的分析手段和借鉴。
[Abstract]:Graded granular materials in geotechnical engineering changes will affect the bearing capacity of the material in the critical state to a great extent, may lead to large deformation structures and even lead to overall instability. Therefore, it is necessary to study the particle size changes on critical state characteristics of materials. Based on the results of numerical experiments through indoor experiment, influence research different initial gradation on mechanical properties of granular materials in critical state; establish relationship between gradation and material critical state, and the introduction of elastoplastic constitutive model, mechanical problems caused by simulation of particle gradation change. (1) a comprehensive laboratory experiment, mechanical properties change with the particle size distribution of sand glass ball and Hostun the relation between the critical state and particle size distribution. The results show that the initial density of materials of undrained shear strength and the transformation ratio of deviatoric stress coefficient Cu with inhomogeneous material increase With the decrease in Cu, and reached 10 after the stable. By the two order power analysis that has great influence the particle size distribution of granular material instability, with the increase of static liquefaction potential of Cu to improve the material, become more unstable. Experiment shows that the nonlinear law of granular materials critical state parameters with the change of particle size distribution index Cu the critical state line in e-p'plane position and slope decreases with widening of particle size distribution in Cu, reaching 10 after both tend to be stable in the q-p' plane. The critical state line of granular materials is a straight line, is not affected by gradation. (2) numerical analysis of multiple should expand the mechanics of particulate material gradation path of force response. Analysis results show that under the same loading condition, the dilatancy decreases with widening the particle size distribution of materials, from the dilatancy to shear the material does not change; The strength decreases with the gradation of broaden the shear. The experimental results further confirmed the nonlinear relationship between the critical state parameters and particle size distribution index Cu, is not affected by the drainage condition and tension shear mode. The critical state line in e-p'plane is the only, and with the widening of the graded down; the critical state line q-p' the plane is a straight line, and gradation. (3) based on meso mechanics analysis, proved that the granular material critical state line in e-p'plane with the mobile grain size distribution and the inherent mechanism and a linear independent gradation in the q-p' plane is indicated by the evolution of the average coordination number of particles in water compared with the shear shear condition has higher stability. In the critical state of the average coordination number and the relationship between the average effective stress is unique, and with the particle size distribution widened down. The stress group structure Contact force analysis showed that the critical state of each particle material micro structure of anisotropic component of meso stress than the same degree of contribution, and has nothing to do with the confining pressure and gradation, thus confirming the linear critical state line for granular materials in the q-p'plane, and has nothing to do. (4) and graded by nonlinear the relationship between the introduction of particle gradation index and critical state, established a graded granular materials dependent elasto plastic constitutive model. The model can describe arbitrary drainage materials and grading of undrained mechanical response. The effect of the gradation of constitutive model were compared with the existing account, it is pointed out that different models to predict the main reason is the relationship between the difference of the effect critical state parameters and grading index. By numerical experiments, some grading index (Cu and Ig) can not accurately describe the mechanical properties of granular material gradation related. This paper puts forward a comprehensive and Cu The new IGU Ig has the advantages of gradation index and used to the improved constitutive model. Simulation tests show that the mechanical properties of the improved constitutive model can better simulate arbitrary graded granular materials. (5) the constitutive model for finite element analysis can be used to develop two times, breaking ground shallow foundation bearing capacity. The constitutive model is compiled into a UMAT subroutine, the bearing capacity of shallow foundation is simulated by ABAQUS. The results of particle breakage caused by the bearing capacity of foundation soil is reduced; with the widening initial particle size distribution, particle breakage gradually weakened the pressure caused by foundation, weak carrying capacity decreased. In summary, constitutive research the results of this study for the sandy soil, micromechanics analysis provide a reference, to provide useful reference and analysis methods of geotechnical engineering problems caused by changes to particle size distribution.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU41

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