多年冻土区桥台台后水平冻胀力的分析研究

发布时间：2018-05-22 16:12

本文选题：多年冻土区 + 桥台　；参考：《兰州交通大学》2017年硕士论文

【摘要】：在多年冻土区铁路的建设和运营过程中,部分桥梁结构出现了一些病害,比如桥台受台后路基填土冻胀力的作用产生了倾斜变形,最终使得梁端与桥台之间的缝隙挤死。对于多年冻土地区桥墩、台变形的研究,我国主要集中在多年冻土区工程病害调查和治理,其重点在于桥墩、台基础的融沉和冻拔变形,桥台的水平冻胀力及变形问题少有研究。2013年底中铁西北研究院在某铁路的调查中发现,某桥西宁端的桥台发生了明显的前倾变形,后经开挖发现,桥台的桩基被剪断。这表明了多年冻土区桥台台后水平冻胀力对桥台危害是存在的,需研究进行治理。本文根据现有的文献资料对多年冻土区桥台台后水平冻胀力的形成机理、影响因素和桥涵病害及其原因进行分析总结;对某典型病害桥梁基础及过渡段路堤病害原因及现状进行分析;并以该桥为分析对象,借助有限元软件ANSYS,建立有限元模型,模拟桥台及周围土体冻结过程的温度场,得出桥台附近的地温场变化特征,并与距桥台较远处土体(不受桥台影响的路基及以下土体)进行了对比分析,得出了桥台对附近的地温场影响较大,增大了土体的换热速度,使周围土体温度场进行了重分布,加快了冻融循环;将该温度场与结构模型进行热-力耦合分析,研究了桥台台后水平冻胀力的大小和发展分布以及桥台受到冻胀力的变形位移情况。通过数值模拟桥台周围的地温场,分析表明距桥台较近的土体其温度变化较快,距桥台较远处受桥台换热边界条件影响很小。与天然地基自上而下的单向冻结过程相比,桥台修建后,桥台附近土体热量发生了变迁,原有的地温热平衡被打破,热平衡条件的改变促使土体的温度状态发生变化,这些变化对桥台稳定性具有不利影响。桥台在台后水平冻胀力作用下向前移动,在台底法向冻胀力和台后水平力共同作用下发生前倾。各个月份的位移值不相同,桥台台后人为上限以上土体随着时间的变化发生着冻融循环。随着冷暖季的交替,桥台和梁体间预留的缝隙不断变小最后挤压在一起,这与实际观测到的现象一致,证明本模型是可靠的。
[Abstract]:In the process of railway construction and operation in permafrost region, some bridge structures appear some diseases, for example, the frost heaving force of embankment after abutment causes slope deformation, and finally causes the gap between beam end and abutment to die. For the study of bridge pier and abutment deformation in permafrost region, our country mainly focuses on the investigation and treatment of engineering diseases in permafrost region, with emphasis on the thawing and freeze-drawing deformation of pier and abutment foundation. The horizontal frost heaving force and deformation of abutment are seldom studied. In the investigation of a railway at the end of 2013, the Northwest Research Institute of China Railway found that the abutment at Xining end of the bridge had obvious forward deformation, and after excavation, the pile foundation of abutment was cut off. This indicates that the horizontal frost heaving force behind abutment in permafrost region is harmful to abutment. In this paper, the formation mechanism of horizontal frost heaving force behind abutment in permafrost region, influencing factors, bridge culvert diseases and their causes are analyzed and summarized according to the existing literature. This paper analyzes the causes and present situation of the foundation and embankment damage of a typical diseased bridge, and takes the bridge as an analysis object, establishes a finite element model with the help of the finite element software ANSYS, and simulates the temperature field of the freezing process of the abutment and the surrounding soil. The variation characteristics of ground temperature field near abutment are obtained, and compared with soil mass (subgrade and soil below) which is not affected by abutment, it is concluded that the influence of abutment on ground temperature field is great and the heat transfer rate of soil is increased. The temperature field of surrounding soil is redistributed to accelerate the freeze-thaw cycle, and the thermal-mechanical coupling analysis between the temperature field and the structure model is carried out. The magnitude and development distribution of horizontal frost heaving force behind abutment and the deformation and displacement of abutment subjected to frost heave force are studied. Through the numerical simulation of the ground temperature field around abutment, the analysis shows that the temperature of soil near abutment changes rapidly, and the influence of abutment heat transfer boundary condition is very small in the distance from abutment. Compared with the unidirectional freezing process of natural foundation from top to bottom, after the bridge abutment is built, the heat of soil around the abutment has changed, the original ground temperature and heat balance has been broken, and the change of thermal equilibrium condition has promoted the change of soil temperature state. These changes have adverse effects on abutment stability. The abutment moves forward under the action of horizontal frost heaving force behind the abutment and tilts forward under the combined action of normal frost heaving force at the bottom of the platform and horizontal force behind the abutment. The displacement values vary from month to month, and the soil above the upper limit of abutment has a freeze-thaw cycle over time. With the alternation of cold and warm seasons the gap between abutment and beam becomes smaller and finally squeezed together which is consistent with the observed phenomenon and proves that the model is reliable.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U442.2

【参考文献】