【作者】 施烨辉；

【导师】 何平；

【作者基本信息】 北京交通大学 ， 岩土工程， 2011， 博士

【摘要】 随着多年冻土区青藏铁路的建设和运营,路基下部地表温度条件发生改变,原天然地表下多年冻土水热状态失去平衡,致使路基下部多年冻土上限迁移,在长期列车荷载和冻融循环作用下,可能会影响路基稳定性。因此,应分析研究冻融循环作用下的路基水热状态,并进行路基热稳定性评价,在此基础上,研究分析长期列车荷载作用对路基稳定性的影响情况,给出未来路基稳定状态作预测。这对路基工程设计、施工及维护有指导性作用,并对铁路运营安全具有重要意义。本文在国家自然科学基金(50778012)支持下,研究分析了冻融循环作用对冻土特性的影响,开展了室内冻土动三轴试验研究,结合现场调研和观测结果,建立模型计算分析了冻融作用下路基温度、水分分布情况,并基于上述研究结果,计算分析了列车荷载和冻融循环作用对冻土路基稳定性影响,取得了以下几个方面的研究成果：(1)开展了多年冻土区段青藏铁路的粉质粘土动三轴试验,给出不同温度、含水量、围压和振动频率条件下动弹性模量、阻尼比、动摩擦角和粘聚力等物理量的变化规律,为计算参数选择提供依据。(2)总结了冻土常用的物理力学等各项表征量,并给出这些表征量对冻土工程性质的具体影响及相关规律。分析得出受冻融循环作用影响较大的几组物理量：干密度、含水(冰)量、弹性模量、抗剪强度、粘聚力等。分析了冻土特殊性质的主要形成过程,即土体的冻结融化过程发生的物理力学行为变化规律。基于已有的试验结果、理论研究和经验成果,给出数值计算可以参照的各项物理力学参数选取规则。(3)基于路基试验段实地观测结果,结合土动力学、传热学、冻土物理学等相关理论建立了冻土路基计算模型,研究了冻融循环对路基温度和含水量分布的影响,提出了基于温度和含水量的路基稳定性评价方法,并对模型路基未来50年的路基稳定状态进行了评价。(4)综合前述研究结果,以青藏铁路为研究对象,建立了车-轨-路基三维有限元计算模型,研究分析了列车移动荷载作用对处于冻结、融化和含冰等条件下冻土路基的影响,对长期列车荷载作用下冻土路基稳定性进行模拟计算并从土体强度和路基变形两个方面作出相应评价,为青藏铁路运营维护提供参考依据。更多还原

【Abstract】 With the construction and operation of Qinghai-Tibet railway in permafrost regions, the surface temperature condition under subgrade has been changed, and the equilibrium state of the water and heat process in perennial-frost which under the natural surface has also been broken, which resulting the migration of upper limit for permafrost under subgrade. Under the effect of long term train load and freezing and thawing cycle, the stability of subgrade will be reduced. As a result, it is important to analysis the water and heat process in subgrade under freeze-thawing cycle and evaluates the thermal stability of subgrade. On this basis, the effect from long term train load to the subgrade stability should be studied and the steady state of subgrade in the future will be predicted. All of these play a guiding role in the design, construction and maintenance for subgrade engineering, and have great significance on the operation safety of railway.In support of National Natural Science Foundation of China (50778012), the effect of freezing and thawing cycle on the properties of frozen soils was studied in this paper. Both laboratory dynamic triaxial test and on-site observation for frozen soils were performed in this study. Based on the experimental results, a computational model was built to analysis the temperature and water distributions under freezing. After that, the influence of train load and freezing and thawing cycle on the stability of frozen soil subgrade was analyzed. The study contained the following main parts:The physical mechanics and thermodynamics characterizing quantities for frozen soils were summarized, and the influence rules of these characterizing quantities on the engineering properties of frozen soils were presented. The following quantities are greatly influenced by the freeze-thawing cycle:dry density, water content, elasticity modulus, coefficient of heat conductivity, slip resistance, cohesive strength, etc. The forming mechanism for the special properties of frozen soils was studied, that is to say, the changing law for the physical and mechanical behavior of frozen soils in the freezing and thawing process was proposed. Based on the existing experimental results, theoretical research basis and empirical achievements, the selection rule of physical mechanics parameters which used in the numerical calculations was also presented.To provide a basis for selecting calculating parameters, an experimental program has been developed. A series of controlled laboratory tests were carried out on silty clay samples from Qinghai-Tibet railway in permafrost regions. It is shown that the physical quantities, such as the dynamic modulus of elasticity, dynamic damping ratio, dynamic friction angle and cohesive strength, are dependent of temperature, water content, confining pressure and vibration frequency. The changing law was proposed at the same time.Based on the on-site observation results at experimental section, a computational model for frozen soil subgrade was established, incorporating soil dynamics, heat transfer theory and physics of frozen soils. On this basis, the effect of freezing and thawing cycle on the temperature and water distributions of subgrade was studied, and a evaluation method for analyzing subgrade stability which taking temperature and water content as indicator was proposed. Using this proposed method, the steady state for the subgrade of the established model in the next fifty years was evaluated.With the above results, and taking the Qinghai-Tibet railway as the object of this study, a 3D FEM model for vehicle-track-subgrade interactions was established. The effects of moving load on the frozen soil subgrade which is freezing, thawing and at iced state were analyzed. The simulations for predicting the stability of frozen soil subgrade influenced by long term train load were carried out, and the results were taken to make evaluations from both the soil strength and subgrade deformation, which providing a reference frame for the operation and maintenance of Qinghai-Tibet railway.更多还原