【作者】 蔡海兵；

【导师】 彭立敏； 程桦；

【作者基本信息】 中南大学 ， 土木工程， 2012， 博士

【摘要】 地铁隧道人工冻结法施工期地层的冻胀融沉现象会对工程周边环境产生不良影响,轻则延长工程工期和提高工程造价,重则危及施工安全和造成重大的经济损失。在地铁隧道冻结工程设计阶段,应根据具体工程性质,采用合理方法对可能引起的地层冻胀融沉效应进行预测,以便于实际施工过程中采取适宜的冻结实施方案和相应的冻胀融沉预防措施,将冻结法应用的成本和风险降到最低。有鉴于此,本文采用理论分析、数值模拟和模型试验相结合的研究手段,对地铁隧道水平冻结工程地层冻胀融沉的预测方法进行了系统研究,并应用于实际工程,对地层的冻胀融沉规律进行深入分析。其主要研究内容及成果如下：(1)提出在地铁隧道水平冻结期,冻结壁交圈前的温度场由单管冻结理论近似求解,冻结壁交圈后的温度场则由平板冻结理论近似求解。基于单管冻结理论、平板冻结理论和土体冻胀率计算公式,考虑冻结壁的形成过程,采用随机介质理论,建立了地铁隧道水平冻结施工期地表冻胀的历时预测模型。(2)提出冻结壁自然解冻条件下的温度场由平板解冻理论近似求解,冻结壁强制解冻条件下的温度场则由单管解冻理论近似求解。基于平板解冻理论、单管解冻理论和一维情况下已融土层的稳定融沉量计算公式,分别考虑冻结壁的自然和强制解冻过程,采用随机介质理论,建立了地铁隧道水平冻结施工期地表融沉的历时预测模型。(3)综合考虑地层温度、地表对流等各类初始和边界条件及土体的冻融相变潜热过程,建立了隧道冻结工程冻融瞬态温度场的数学模型,并定义冻土的冻胀率和融沉率为瞬时体应变,考虑冻土的正交各向异性变形特征,基于ABAQUS有限元软件的二次开发技术,编制土体冻融变形的用户子程序,进而提出了地铁隧道水平冻结施工期地层冻胀融沉的弹塑性热力耦合数值模拟预测方法。(4)将所提出的冻胀融沉随机介质理论预测方法和热力耦合数值模拟预测方法,应用于圆形隧道全断面水平冻结工程和浅埋大断面隧道水平冻结工程中,获得了地层冻结温度场、冻胀位移场、解冻温度场以及融沉位移场等分布规律,并与现场实测结果相比较,验证了预测方法的实用性和可靠性。(5)首次建立了一套可模拟地铁隧道双线水平冻结施工过程的室内原材料模型试验系统,对双线隧道依次冻结方式下的地层温度场和冻胀融沉变化规律进行了试验研究。通过数值模拟分析验证了模型试验结果的可靠性,且表明相对于同时冻结方式,双线隧道采用依次冻结方式在一定程度上能减小地层冻胀位移。在今后地铁隧道建设中,人工冻结法的应用将会越来越广泛。本文研究成果将为此类工程建设提供有效参考依据,并具有重要的现实工程意义。更多还原

【Abstract】 In the period of subway tunnel construction with artificial freezing method, frost heave and thawing settlement of ground can produce serious influence on the surrounding environment, ranging from extending construction period and increasing project cost to endangering construction safety and cause significant economic losses. In the design phase of subway tunnel freezing engineering, reasonable method must be adopted to forecast possible frost heave and thawing settlement effect of ground according to the specific project, on this basis, suitable freezing implementing scheme, frost heave and thawing settlement prevention measures can determined, which can reduce the project cost and construction risk. For this reason, by means of theoretical analysis, numerical simulation and model test, prediction methods of frost heave and thawing settlement are researched in the period of subway tunnel construction with horizontal freezing method in the thesis. Aiming to practical engineering, the proposed prediction methods are used for in-depth analysis on the distribution law of frost heave and thawing settlement. Research contents and achievements are as follows:(1) Temperature field before freezing wall enclosing can be analyzed by single-pipe freezing theory, and temperature field after freezing wall enclosing can be analyzed by flat-panel freezing theory. Based on single-pipe freezing theory, flat-panel freezing theory and frost heaving rate calculation formula, considering the formation process of frozen wall, using stochastic medium theory, a duration prediction model of surface frost heave in the period of subway tunnel construction with horizontal freezing method is presented.(2) Temperature field under natural thawing conditions can be analyzed by flat-panel thawing theory, and Temperature field under mandatory thawing conditions can be analyzed by single-pipe thawing theory. Based on flat-panel thawing theory, single-pipe thawing theory and thawing settlement content calculation formula in the one-dimensional case, considering the thawing process of frozen wall, using stochastic medium theory, a duration prediction model of surface thawing settlement in the period of subway tunnel construction with horizontal freezing method is presented.(3) Considering various initial and boundary conditions such as ground temperature, surface convection and freezing and thawing phase change latent heat, etc, Mathematical model of freezing and thawing transient temperature field is presented. Defining frost heave rate and thawing settlement rate of frozen soil as instantaneous volume strain, considering orthotropic deformation characteristics of frozen soil, based on secondary development of ABAQUS finite element software, user subroutine used to calculate freezing and thawing deformation of frozen soil is compiled, and then coupled heat-stress numerical simulation prediction method of frost heave and thawing settlement is proposed in the period of subway tunnel construction with horizontal freezing method.(4) The stochastic medium theory and coupled heat-stress numerical simulation prediction methods of frost heave and thawing settlement are applied to circular tunnel full section horizontal freezing engineering and shallow large section tunnel horizontal freezing engineering, then freezing temperature field, frost heave displacement field, thawing temperature field and thawing settlement displacement field are presented, which are compared with field measured results to verify reliability of the prediction methods.(5) A large raw material model test system is firstly established, which can simulate two-lane tunnel horizontal freezing construction process. Ground temperature field, frost heave and thawing settlement variation are researched by model test in the case of two-lane tunnel sequentially freezing. Through numerical simulation analysis, the model test results are be verified. Frost heave displacement can be reduced when two-lane tunnel sequentially freezing compared with simultaneously freezing.The application of artificial freezing method will be more widely used in subway tunnel construction in the future. Achievements of the thesis not only can provide effective reference for such tunnel engineering construction, but also have great realistic engineering significance.更多还原