桩网结构低路基土拱效应及加筋垫层动力特性研究

发布时间：2018-04-19 21:48

本文选题：桩网结构路基 + PFC离散元　；参考：《北京交通大学》2015年硕士论文

【摘要】：桩网结构路基的桩、加筋垫层和土体相互作用强烈,尤其路基高度较低时,基床受列车荷载影响较大,路基中的土拱效应及张拉膜效应会发生变化从而影响桩网结构路基功能的发挥。研究列车荷载下桩网结构低路基土拱效应及垫层中土工格栅特性具有重要的理论意义和工程价值。本文运用PFC3d离散元软件建立了桩网结构路基简化模型对土拱效应进行了细观研究分析,进而基于遂渝线现场动车试验测试断面运用ABAQUS有限元软件建立三维桩网结构路基动力模型,对列车荷载作用下桩网结构低路基的土拱效应和土工格栅受力及变形开展研究,本文主要内容及结论如下： 1、运用PFC3d软件建立桩网结构路基简化模型模拟土拱效应,对颗粒间的接触力链,颗粒的竖向及横向位移,路基的竖向应力分布等进行分析,表明桩土发生差异沉降后路基中会形成应力拱,应力拱内包含多个虚拟土拱。动荷载作用时路基中会形成动力土拱,动力土拱的高度与动荷载的大小有关且动力土拱高度要低于静力土拱。位移拱范围内桩顶上方颗粒的横向位移较大,向四周逐渐减小。等沉面形成与位移拱有关,位移拱范围内桩顶上方颗粒挤入桩间土区域从而导致位移拱范围外桩顶上方颗粒竖向位移增大而桩间土上方颗粒竖向位移减小。 2、运用ABAQUS软件建立三维桩网结构低路基动力模型,采取相应方法对列车荷载、动力边界等条件进行设定。现场动车测试与模拟计算的动应力、动位移结果对比验证了本文所建模型的可靠性。 3、基于动力有限元模型分析列车荷载作用下桩网结构路基中竖向应力分布、等沉面高度、桩土应力比等变化规律,表明列车荷载作用下路基中动应力的分布会受到土拱效应影响,表现为桩间土上方的动应力转移到桩顶上方且在土工格栅附近转移现象最明显。列车荷载作用过程中,桩土应力比峰值逐渐减小且趋于稳定。布置桩体纵断面的等沉面高度大于没有布置桩体纵断面的等沉面高度,且沿路基中心到路肩同一类型纵断面的等沉面高度降低,列车荷载作用后路基中心处的等沉面高度升高。另外分析了桩间距、路基高度、桩端土体模量等因素对土拱效应分析参数及其在列车荷载作用后变化的影响规律。 4、分析列车荷载作用下的土工格栅受力及变形规律,表明路基中心处桩顶上方土工格栅竖向位移要小于桩间土上方土工格栅竖向位移。横向土工格栅竖向变形量及变形变化量要大于纵向土工格栅。垂直桩帽边的纵向土工格栅动位移要大于平行桩帽边的纵向土工格栅动位移,横向土工格栅动位移从路基中心到坡脚呈现递减规律。路基中心桩帽边缘处土工格栅拉力及动拉力大于桩间土及桩帽中心处土工格栅,横向土工格栅最大拉力及动拉力大于纵向土工格栅。垫层布置双层土工格栅相对单层土工格栅能够减小路基沉降及不均匀沉降,能够提高路基抵抗列车荷载造成路基不均匀沉降的能力,并有利于土工格栅在列车荷载下的受力稳定。另外分析了桩间距、路基高度、桩端土体模量等因素对土工格栅拉力及变形及其在列车荷载作用后变化大小的影响规律。
[Abstract]:Pile net structure subgrade pile, reinforcement cushion and soil interaction are strong, especially when the height of subgrade is low, the foundation bed is influenced by train load, soil arch effect and tensioned effect in subgrade will change to influence the function of pile network structure subgrade. The characteristics of grille have important theoretical significance and engineering value.
In this paper, a simplified model of pile net structure subgrade is established by using PFC3d discrete element software, and the soil arch effect is studied and analyzed. Then the dynamic model of the three dimensional pile network structure is established based on the test section of the field train test and test section of the Suu Yu line, and the soil arch effect of the Low Subgrade under the load of the pile network under the load of the train. The main contents and conclusions of this study are as follows:
1, using the PFC3d software to establish the simplified model of pile net structure to simulate the soil arch effect. The contact force chain, the vertical and lateral displacement of particles, the vertical stress distribution of the subgrade are analyzed. It shows that the stress arch will be formed in the Subgrade after the difference settlement of the pile and soil, and several virtual soil arches are included in the stress arch. The subgrade of the subgrade is the dynamic load. The dynamic soil arch is formed, the height of the dynamic soil arch is related to the size of the dynamic load and the height of the dynamic soil arch is lower than that of the static soil arch. The lateral displacement of the particles above the top of the pile is larger and gradually decreases to the surrounding area. The formation of the equal subsidence surface is related to the displacement arch, and the particles in the top of the pile top are squeezed into the soil area between the piles and thus lead to the soil region. The vertical displacement of particles above the top of the pile outside the displacement arch range increases, while the vertical displacement of the particles above the pile decreases.
2, the dynamic model of the Low Subgrade of three dimensional pile network structure is established by using ABAQUS software. The corresponding method is adopted to set the train load and the dynamic boundary conditions. The dynamic stress and the dynamic displacement results of the field EMU test and the simulation results verify the reliability of the model built in this paper.
3, based on the dynamic finite element model, the vertical stress distribution in the subgrade of the pile net structure under the load of the train is analyzed. The variation law of the height of the subsidence surface and the stress ratio of the pile and soil shows that the distribution of the dynamic stress in the subgrade under the load of the train will be influenced by the soil arch effect, which shows that the dynamic stress above the pile soil is transferred above the pile top and in the geotextile. The transfer phenomenon near the gate is most obvious. In the course of the train load, the stress of the pile and soil decreases gradually and tends to be stable. The height of the equal subsidence surface is greater than that without the longitudinal section of the pile body, and the height of the equal subsidence surface along the same type of longitudinal section along the center of the roadbed is reduced, and the Subgrade after the train load is loaded. In addition, the analysis parameters of the pile spacing, the height of the subgrade and the soil modulus of the pile end on the analysis parameters of the soil arch effect and its influence on the change after the train load are also analyzed.
4, the stress and deformation law of geogrid under the load of train indicates that the vertical displacement of the geogrid above the pile top is less than the vertical displacement of the geogrid above the pile. The vertical deformation and deformation of the lateral geogrid is greater than that of the longitudinal geogrid. The dynamic displacement of the longitudinal geogrid is greater than that of the parallel pile cap. The dynamic displacement of the lateral geogrid is decreasing from the center of the subgrade to the foot of the slope. The tensile force and the dynamic tension of the geogrid at the edge of the pile cap at the center of the subgrade is greater than the geogrid at the center of the pile and the pile cap. The maximum pulling force and the dynamic pulling force of the lateral geogrid are greater than the longitudinal geogrid. The layout of the double layer geogrid relative to the single layer geogrid can reduce the settlement and uneven settlement of the roadbed, which can improve the ability of the subgrade to resist the uneven settlement of the subgrade by the train load, and is beneficial to the stability of the geogrid under the train load. In addition, the pile spacing, the height of the subgrade and the soil modulus of the pile end are also analyzed. The influence of grid tension and deformation on the change of train load is discussed.

【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U416.1

【参考文献】