【作者】 李存兴；

【导师】 别社安；

【作者基本信息】 天津大学 ， 港口、海岸及近海工程， 2008， 硕士

【摘要】 在软土的沉降分析中,必须考虑软土的蠕变特性,否则分析结果就可能会出现较大的偏差。箱筒型结构是一种适合于软土地基上的基础结构,它具有结构重量轻、稳定性易于满足、施工方便、工程费用低等特点,有良好的推广前景,但关于这种结构沉降量特性的研究比较少。本文将在较为系统地阐述土的流变理论的基础上,以天津港北大防波堤延伸工程为背景,以箱筒型结构室内沉降实验为基础,采用PLAXIS 3D FOUNDATON有限元软件建立有限元模型,来分析箱筒型基础的沉降变形随着结构宽度深度和土体参数等影响因素变化的规律,这对工程设计有重要意义。研究过程中,本文进行了平板型、方筒型和圆筒型基础结构的室内沉降试验,然后结合PLAXIS软件,使用软土蠕变模型对室内试验进行模拟,模拟结果较好的符合试验数据。接着,采用有限元软件分析研究了结构形式(平板、方筒、单圆筒、箱筒型)、结构尺寸(包括箱筒型基础结构的宽度和入土深度)、外部荷载、土体参数(包括渗透系数、初始固结度、粘聚力和内摩擦角、土与界面单元摩擦参数、修正压缩、膨胀、蠕变指数等)、以及边界条件对箱筒型基础沉降量的影响,并得出相应的结论。同时还模拟了三维结构延伸至二维的情况,模拟了持久水平力作用下的位移响应情况。分析表明,采用箱筒型基础结构形式,适当增加入土深度,控制结构宽度(20m-26m),减缓加载速度,提高土体渗透系数,提高土体强度等对于控制和减小结构最终沉降量有着非常明显的作用。文章最后提出了箱筒型基础的沉降计算进行简化方法。运用土力半径确定影响范围并引入沉降折减系数,同时运用规范所推荐的分层总和法计算沉降、并结合箱筒型基础和等底埋深的刚性基础的模拟结果的对比,进行求解折减系数。计算结果表明,折减系数随着结构宽度和深度的增加而变大。这一思路能够较好解释所模拟的现象。这为估算箱筒型基础沉降量提供了参考,也为以后研究做了铺垫。但是这方面更加深入的研究有待继续。更多还原

【Abstract】 In the settlement analysis, the creep of soft soil should be considered, otherwise the deviation may be occurred. Box is a tube-type structure, suitable for soft ground on the infrastructure. It is a light weight structure, which is easy to meet the stability to facilitate the construction and thus to make the cost low. Given these traditions, it has a good promotion prospects, but the study of such a structure on the settlement is quite few. On the basis of the indoor settlement study of the box structure, this paper, with the Tianjin harbor breakwater serving as the engineering background, will analysis the law that deformation of the settlement changes as the depth and width of the structure and soil parameters changes through using systematical theory of the evolution soil and PLAXIS 3D FOUNDATON models. The results will be far-reaching for engineering design.During the study, first, flat type, the tube and cylinder-type settlement infrastructure indoor tests is carried out, second, then, PLAXIS 3D FOUNDATON models are built to simulate the tests. The simulation results are quite agree with the test data. Then, the type and size of the structure, external loads, soil parameters and the impact of boundary conditions for box and bucket foundation settlement are analysised by using finite element analysis software. Meanwhile, tests that three-dimensional structure extended to the two-dimensional one and the response to the displacement responses to the sustaining horizontal level power on the structure are simulated. The analysis show that the use of tube-shaped boxes of infrastructure to appropriately increase entering soil depth, the control structure width (20m-26m), slow loading speed and improve soil permeability coefficient, improve soil strength lead a significant role in controlling and reducing the structure of final settlement.In conclusion, the paper proposes methods to simplify the settlement calculation of the box and bucket foundation. The reduction factor is figured out by using soil mechanics radius to determine the affected areas, introducing the settlement reduction Coefficient, using hierarchical integrated methods, and comparing the box and bucket foundation to the same depth rigid foundation. The result shows that reduction factor is in linear growth as the width and depth increases. This line of thought can be better explained by the simulation of the phenomenon. The phenomenon can be better explained by this line of thought. It will support some recommendation for settlement calculation of box and bucket foundation. But in this respect more in-depth study is to be continued.更多还原