【作者】 马立峰；

【导师】 刘建坤；

【作者基本信息】 北京交通大学 ， 道路与铁道工程， 2011， 博士

【摘要】 多年冻土区斜坡段路基稳定性对铁路长期运营具有潜在的威胁,随着道路建设及运营,改变了原天然地表与大气之间的热量平衡条件,打破了原多年冻土的水热平衡状态,导致路基下伏多年冻土天然上限发生改变,加之常年列车荷载及可能发生地震的条件下,出现路基病害的可能性大。针对出现的路基病害,分析其病害特征、产生机理,并进行稳定性评价,对路基工程设计、施工及道路维护有指导性作用,对保证铁路的安全运营具有重要意义。本文在国家“十一五”科技支撑项目《青藏铁路运营安全保障系统研究》中“多年冻土工程检测与病害防治技术研究”课题之子课题“冻土斜坡路基的稳定性评价与整治措施研究”支持下,以现场调研及实测为基础,开展了室内静、动力学试验研究及室内模型试验研究,并通过数值模拟计算方法,进行了动荷载条件下多年冻土区斜坡路基动力响应分析,取得了以下几个方面的研究成果：(1)进行实地调研并选取试验路段,开展试验段典型土样的室内基本土性分析试验,掌握其基本土性特性,进行土样的工程分类；进一步开展了冻结粉质粘土静、动三轴压缩试验研究,分析不同温度、不同含水率及不同围压条件下冻土强度、动弹性模量变化趋势,并总结了不同试验条件下冻土强度、动弹性模量、动剪切模量及动阻尼比的试验结果。(2)通过室内三轴压缩试验,分析了粉质粘土及砂砾土饱水后其土体强度的变化；考虑路基表面不同动荷载条件、冻土斜坡路基不同温度分布及不同含水率条件,开展了室内模型试验以模拟季节融化期列车荷载条件下冻土斜坡路基的稳定性状况,分析了试验过程中冻土斜坡路基模型的温度变化及变形特征,通过含水率的测试,分析了试验过程中水分迁移特征,阐述了冻土斜坡路基的破坏形式及破坏位置,指出了冻土斜坡路基的潜在滑动面。(3)通过数值模拟计算方法,分别对地震荷载及列车荷载条件下冻土斜坡路基动力响应进行了研究,分析了地震条件下不同频率地震波、不同坡度、不同路基断面形式对冻土斜坡路基稳定性的影响和列车荷载条件下坡度对斜坡路基稳定性的影响。(4)总结分析了室内试验、模型试验、地震荷载及列车荷载作用下斜坡路基响应等研究成果,充分考虑所有的影响因素,利用层次分析法(AHP)结合模糊数学理论,提出了基于可靠度的多年冻土区斜坡路基稳定性评价方法。更多还原

【Abstract】 Complicated geological conditions in permafrost regions, in particular, permafrost and seasonal frozen soil are the key issues to construction and stability of engineering. The completion and operation of the Qinghai-Tibet Railway has a major political and economic significance. However, the highest intensity of seismic activity in Qinghai-Tibet Plateau must be considered. Dynamic response and stability analysis of the embankment along the slope section of Qinghai-Tibet Railway are researched in this paper. The main conclusions are as follows:On-site soil samples are mainly consisted of silty clay and gravel. The frozen soil strength increases linearly with the decreasing of the temperature. The frozen soil strength decreases with increasing water content. And with the water content increasing, the decreased intensity of strength gradually reduces. Under the conditions of confining pressure<2Mpa, the frozen soil strength changes in a small range.Dynamic elastic modulus of the frozen soil increases with the decreasing temperature. And the temperature is more important as influencing factor than confining pressure. Under the higher water content conditions, dynamic elastic modulus decreases with increasing water content. However, dynamic elastic modulus increases with increasing water content under the lower water content conditions.Triaxial shear tests and saturated soil triaxial compression tests show that the shear strength of saturated soil decreased significantly.Under dynamic loading, laboratory model test of embankment on slopes in permafrost region is carried out. The studies show that the water of embankment and slope infiltrates along with the gradual deepening of freeze-thaw interface by the action of gravity. And the water is enriched at the toe along the freezing interface. The strength of the soil reduces because of high water content of freeze-thaw interface. Under dynamic load conditions, the destruction form of roadbed and slope is mainly longitudinal cracks along the slope and embankment. Another mainly form is dislocation slip along the potential sliding surface. And the potential sliding surfaces are mainly distributed in freeze-thaw interface, the interface of soil and the toe. For the stability of embankment on slopes in thawing period, the main influencing factors are the slope gradient, dynamic stress on embankment surface and the distribution of water.The numerical simulation is carried out to analyse stability of embankment on slopes in permafrost regions under earthquake loading. As for the deformation, shear strain and displacement of the whole model, the velocity and acceleration of the key points, high-frequency seismic wave impacts more significantly than low-frequency wave. That is to say, high-frequency seismic wave is more dangerous to the stability of embankment on slopes in permafrost regions. And subgrade cross section type is also an important factor to the stability of embankment. The maximum lateral displacement arises at the surface of roadbed, and the maximum shear strain arises at the freeze-thaw interface.The simulation results of stability of embankment on slopes in permafrost regions under train load show that the main impactive depth of vertical displacement increases with increasing slpoe gradient. The most obvious deformation and the maximum shear strain arise at the saturated silty clay. In a word, the saturated silty caly and the slope gradient are the key factors to the stability of embankment.The stability of embankment on slopes is considered as a special form of embankment stability in permafrost regions. And the AHP-Fuzzy synthetic evaluation method is adopted in the thesis. In the analysis of stability of roadbed in permafrost regions by AHP-Fuzzy synthetic evaluation model on the basis of reliability, the relationships of each influencing factor are completely considered. And the stability of roadbed is not only evaluated qualitatively but also given the accurate evaluation score. This method is effective to evaluate the stability of roadbed in permafrost regions.更多还原