【作者】 金顺浩；

【导师】 柳俊哲；

【作者基本信息】 东北林业大学 ， 森林工程， 2013， 博士

【摘要】 本研究以土工格室为研究对象,通过土工格室加筋土的抗弯承载特性和筋土界面特性的试验研究,探讨土上格室加筋土的加固机理。本研究通过承载力室内模型试验,得到PIV画像解析图片,利用PIV画像解析方法和数字图像处理技术,对地基内部砂的运动,细观结构的图像进行定量和定性分析,得出地基砂土在条形均布荷载作用下,加筋前后各项参数和各种应力、应变场的变化规律。在模型试验中将变形量测系统用于分析加筋地基加载变形破坏的位移、地基内部局部剪应变场的图像,用以研究加筋地基的破坏模式和破坏面发展机理。采用有限元模拟分析地基砂内部的局部应力状态,解析地基砂内外部的应力场、应力路径及内力变化。本研究将基础模型按照实际基础同比例缩小进行加筋土界面特性的试验研究实验,利用拉拔试验装置和位移计测土体内部位移连续变化进程,得到土工格室拉拔抵抗力产生的原理模式图像和土工格栅位移与拉拔抵抗力的分布状况图像,比较分析土工格室和土工格栅的拉拔特性,研究土工格室和土工格栅的位移传递机制。通过静承载力试验和纸状的压力传感器测定应力分布,对补强机理、应力分散效果进行探讨。利用应力测定系统,研究加筋土的网兜效应和抗弯刚性及应力分散效果。最后通过现场简易承载力试验比较不同种类补强材料的补强效果,复核土工格室模型与原型的系统相似定理。本研究利用以上方法,追踪加筋土地基的渐进性变形与破坏过程,捕捉加筋土地基的变形模式、滑动剪切面位置形状和剪切带特征。为研究砂土在拉拔水平荷载下的全场位移和局部位移的产生、发展和演化特点进行了量测和定量分析。PIV画像解析表明无土工格室补强地基内速度向量分布是在载荷板正下方往正中心方向运动显著,速度大,表明载荷板正下方应力集中,土工格室补强地基内速度向量分布是在载荷板正下方出现横方向的运动,速度小且均匀,表明应力集中现象被冲散。变形量测系统分析表明纯砂或无补强时地基内部砂在剪切过程中,最大剪应变的方向均在约10°的破裂线上,而土工格栅加筋土剪应变等值线,即最大剪应变几乎发生在水平方向上,且该水平面与筋材的布置十分一致。有限元模拟分析表明加筋砂土地基内部的高补强效果在局部应力状态已接近破坏状态,且破坏区域扩散后才表现出来。加筋土界面特性研究表明土工格栅应变软化来得快,应变软化开始直接进入到相当小的残留强度状态；而土工格室是应变软化来得迟,先显示出稍高的最大抵抗力,以后应变软化较短,最后表现出相当大的残留强度。土工格室的内部位移是从墙壁近旁开始向后方进行传播,其进展性土工格栅比土工格室更显著。应力扩散试验表明土工格栅、土工格室加筋土地基的应力曲线在中心附近的尖顶分布,而土工格栅配合土工格室加筋土地基的应力曲线在中心附近较宽阔范围内缓慢分布,即后者比前者应力扩散效果好。土工格栅配合土工格室加筋土地基承载力较大,而碎石作为填料使用时,土工格室碎石加筋土地基承载力比土工格栅配合土工格室加筋土地基承载力还大。土工格室与土工格栅主要区别在于,前者因具有一定的厚度,固具有一定的抗弯能力,能有效扩散从上部结构传来的竖向应力；同时发挥类似于“深基础”的作用,大大提高地基的承载能力。实验结果表明,有限元数值模拟的细观力学特性与土体的宏观力学现象密切相关,有限元法数值模拟技术分析研究加筋地基的承载力和变形特性是可行的。物理模型试验PIV图像的细观结构的变化特征,反应了土体的宏观力学响应特性,说明了通过对土体的PIV细观结构变化来反应土体破坏前后的强度和变形的可行性。通过对这两种细观观测结果进行关联性分析,同时与宏观试验结果进行对比分析,结果表明PIV图像的细观结构的变化特征与宏观力学响应特性具有很好的一致性。土工格室作为一种新型建筑材料具有良好适应性(适应多种填料)、良好的经济性(工程项目上应用土工格室最多节约达30%的投资)及良好的稳定性,土工格室工法能有效利用现场土质,减少土石方量,有效削减环境负荷,加快工程进度。对土工格室加筋结构的作用机理的研究还有待深化,提出一种实用的工程设计计算方法是当务之急。更多还原

【Abstract】 Object of this study was geocell, which is geotechnical construction material using subgrade material as the main body. Purpose of this study was to investigate the mechanism of reinforcement effect of geocell reinforced soil through the experimental research on the bearing capacity of geocell reinforced soil and characteristics of the interface between reinforcement and soil.In this study, PIV analysis images were obtained by the bearing capacity of indoor model test. Quantitative and qualitative analysis for internal sand movement of foundation and meso-structure images by using PIV image analysis method and digital image processing technology to get the change regularity of parameters, various stress and strain fields before and after reinforced in the strip of sand foundation under uniformly distributed loads. In model tests, displacement of reinforced foundation loading deformation and foundation internal local shear strain field image were analyzed using Deformation Measurement System to investigate the mechanism of reinforced foundation failure mode. Foundation internal local stress state results, stress field, stress path and stress variation were analyzed using Finite Element Simulation analysis. In this study, the basic model according to the actual same scaling was used in the test for reinforced soil interface charisteristics. Measuring process continuous change of internal displacement of soil by pull-out test device and displacement; comparing the pullout behavior of geocell and geogrid and studying displacement transfer mechanism of geocell and geogrid. Stress distribution determined by static bearing capacity tests and paper-like pressure sensor, in order to investigate the effect of stress dispersion and reinforcement mechanism. Discussing reinforced soil elastoplastic mattress effect, bending rigidity and stress dispersion effect by the stress measurement system. Finally, a simple site load test was used for comparison of reinforcement effect with different reinforcing material, and review similar theorem of geocell model and the prototype system.In this study, using above methods, tracked the progressive failure process and deformation of reinforced soil, captured deformation mode, sliding shear plane position shapes and shear zone of reinforced soil. Carried the measurement and quantitative analysis for the displacement occurred in drawing horizontal load of sand, development and evolution characteristics of the partial displacementPIV image analysis indicated that velocity vector distribution in the no geocell reinforced foundation showed obvious movement with high speed to the positive direction of the center beneath the load plate, which means that the stress concentration below the load board; while in occasion of geocell reinforced foundation, velocity vector distribution showed cross direction movement with small and uniform speed, which means that the phenomenon of stress concentration were dispersed. Deformation Measurement System analysis showed that in occasion of pure sand or no reinforcing, the maximum shear strain direction was almost at about10°rupture line for foundation internal sand in shear process. While Geogrid reinforced soil shear strain contour line, that the maximum shear strain almost occurred in the horizontal direction, and the horizontal plane was consistent with reinforcement layout. Foundation internal local stress state results were analyzed using Finite Element Simulation Analysis and showed that high reinforcing effect in the local stress state is close to failure state and shown after the failure field diffusion. In pullout test, geogrid displacement weak segment came faster and directly into state of residual small strength; however for geogcell, displacement weak segment came later, first showed slightly higher maximum resistance than the former, after short displacement weak segment, finally showed residual strength. Internal displacement of geocell model spread beginning from the wall to the back, its progress was less significant than geogrid. Stress diffusion test showed that stress curve distribution of geogrid or geocell reinforcd soil was in the vicinity of the spire. Meanwhile, for geogrid combined geocell type, stress curve was distributed in wide range near the center. Foundation bearing capacity was improved when geogrid combined with geocel. When gravel used as filler, bearing capacity of gravel reinforced geocell was larger than that of geogrid combined with geocell.Main difference between geocell and geogrid is that geocell has a certain thickness and a certain bending ability, therefore can effective diffusion the vertical stress from the superstructure; at the same time play a role similar to the "deep foundation", greatly improved the bearing capacity of foundation.The results indicated that using Finite Element Simulation Analysis, the variety feature of micro-structure is consistent with the macroscopic mechanical response feature. Finite Element Simulation analysis is feasible for studying on bearing capacity and deformation characteristic of reinforced foundation. The variety feature of physical model test PIV images reflect macroscopic mechanical response feature of soil, that means the feasibility for response strength before and after failure and deformation of soil by the microscopic structure change. Comparing the relationship analysis of two types of micro-structure with the macroscopic test results indicated that PIV images of micro-structure is consistent with macroscopic mechanical response feature.Greocell as a new type of building material, that has good adaptability (adapt to variety filler), good economy (application of geocell can save up30%of investment) and good stability. Geocell method can effectively use the field soil, reduce earthwork, effectively reduce the environmental load and speed up the progress of works. Study on the mechanism of geocell reinforced structure remains to be deepening. To propose a practical engineering design calculation method is a priority.更多还原