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1、摘 要 - I - 摘 要 随着青藏铁路的通车，由列车荷载振动效应引起冻土路基的沉陷问题日益显 著，直接关系到客货列车的安全营运、能否提速等关键科学问题。鉴于此，本论 文以青藏铁路高温极不稳定多年冻土区路基在气候变化和列车荷载共同作用下的 长期服役性能为应用背景，采用室内试验、理论分析和数值模拟相结合的技术手 段，对青藏铁路列车荷载下冻土、融土的动力变形特性、列车荷载下路基振动反 应和长期列车荷载作用下路基动力永久变形等科学问题进行了基础性研究，主要 研究内容与取得的成果如下。 (1) 针对不同的动应力条件、环境温度和土体物理状态，通过低温动三轴试 验，分析了冻结粉质粘土的动力变形特性，研究了
2、列车荷载下冻土的弹性变形 和累积塑性变形的变化规律，建立了冻土回弹模量的经验模型；并以临界动应力 为归一化因子，进一步建立了冻土累积塑性应变与动应力条件、振动次数和冻结 温度等参数之间的关系模型。 (2) 针对冻融循环与列车荷载作用特点，基于常温动三轴试验，研究了冻 融循环次数、融化温度、动应力幅值等对融化粉质粘土的动态力学行为的影 响，深入研究了冻融循环和列车循环荷载综合作用下融土的弹性变形和累积变 形变化规律，并建立了回弹模量和累积塑性变形与冻融循环次数之间的关系模 型，与以上建立的模型一并为后续计算分析青藏铁路路基永久变形提供依据。 (3) 针对青藏铁路路基的场地条件，采用有限元无限元相
3、结合手段，研究 了列车行驶对多年冻土区路基三维振动反应的数值模拟途径。实现了温度场和 应力场耦合，探讨了列车速度、轴重与路基的主要设计参数对路基振动反应的 影响规律，并借助正交试验设计原理，对各影响参数的敏感性进行评价。 (4) 以建立的列车荷载下冻结、 融化粉质粘土的累积永久应变模型为基础， 二次开发了接口于粘弹塑性本构模型的 CREEP 子程序， 建立了列车行驶路基累 积永久变形预测模型。并基于该模型探讨了列车轴重、速度、等效振次和冻融状 态等因素对路基累积永久变形发展的影响。 关 键 词 ：青藏铁路；多年冻土区；冻融循环；列车荷载；振动反应；永久变形哈尔滨工业大学工学博士学位论文 - I
4、I - Abstract With the completion of the Qinghai-Tibet Railway, several damages induced by the traffic loads have been occurring to the permafrost subgrade, and the safe-operation demand and speed-increasing scheme of the railway will therefore be affected seriously. In view of this, considering the
5、background of the long term operating performance of the ice-rich permafrost sloped-subgrade along the QTR subjected to traffic loads and annually changing climate, the present thesis attempts to present relevant fundamental researches on such key issues as the dynamic performance of frozen and thaw
6、ing soil, the vibration response of the subgrade, and the permanent deformation induced by traffic loads. Laboratory tests, theoretical analysis and numerical simulation are taken as the main technological measures to perform the investigation. The original work is presented in detail as follows. (1
7、) Based on the Cyclic-dynamic triaxial tests, the dynamic behavior of frozen silt clay of the QTR subgrade subjected to the variation of dynamic stresses, of external environmental conditions, and of physical features of soil is examined, and emphasis is also given to the evolution of elastic deform
8、ation and cumulative plastic deformation of frozen silt clay induced by vibration loads. Specifically, a resilient modulus-based-model is established on the basis of the obtained data, and the relation model between cumulative deformation and such parameters as dynamic stresses, number of vibration,
9、 and frozen temperatures is proposed as well, taking critical dynamic stress as the normalization factor. (2) With the above-mentioned tests performed, a further research of the influence of freezing-thawing cycles, thawing temperature, amplitude of dynamic stresses on the mechanic features of the f
10、rozen silt clay of the QTR sloped-subgrade is carried out, in view of the characteristics of seasonally frozen soil and traffic loads. Special attention is paid to the development of elastic and cumulative deformation of silt clay subjected to both freezing-thawing cycles and traffic loads, and anot
11、her relationship model of resilient modulus, cumulative plastic deformation and freezing-thawing cycles is obtained, which together with the model mentioned above can provide theoretical foundation for the later calculation of permanent deformation of the QTR Abstract - III - sloped-subgrade. (3) A
12、three dimensional finite element-infinite element model on the vibration response of the QTR sloped-subgrade is established. Our teams train-track-subgrade vibration program is adopted to simulate the traffic loads, that is, the calculated track-sleeper forces, and the obtained forces are then impos
13、ed on the three-dimensional sloped-subgrade model so that the temperature field can be coupled with the stress field. The effects of primary parameters such as travelling velocity, train axle, and subgrade on the vibration response of sloped-subgrade are compared based on the simulation results, and
14、 the sensitivity analysis of parameters is performed trough intersection experiment design principle, by which the mechanism on the dynamic characteristics of the sloped-subgrade of warm permafrost region is further clarified. (4) On the basis of the established cumulative-permanent-strain model of
15、frozen and thawed silt clay subjected to cyclic traffic loads, the Drucker-Prager-based visco-elastic plasticity sub-program CREEP is developed. Taking the well-obtained dynamic stresses of subgrade as the initial state variable, the numerical model on the permanent deformation of the QTR subgrade c
16、onsidering both the effects of ground pressures and dynamic stresses is built, based on which the permanent deformation of sloped-subgrade induced by traffic loads is predicted, and the influence of train axle, traveling velocity, and vibration numbers on the permanent deformation is investigated. Keywords: Qinghai-Tibet Railway； permafrost region； freezing-thawing cycles； traffic loads；vibration response；permanent deformation
