【作者】 李永强；

【导师】 张鲁新；

【作者基本信息】 兰州大学 ， 地质工程， 2008， 博士

【摘要】 青藏铁路格(尔木)——拉(萨)段全长1142km,其中穿越大片连续多年冻土区546.41km(其间分布的融区总长为101.68km),位于多年冻土区的路基总长为321.706km,占多年冻土区总长444.73km的72.3%。线路跨越海拔高程4000m以上的地段约为965km,“高寒缺氧”、“多年冻土”和“生态脆弱”问题是青藏铁路建设的三大技术难题,而多年冻土居于青藏铁路建设和运营的三大难题之首。因此有“青藏铁路成败的关键在路基,路基成败的关键在冻土”之说。整个工程建设从2001年6月29日开始,至2006年7月1日正式开通运营。为有效保护多年冻土,维持其上路基工程的稳定性,青藏铁路在修建时,针对多年冻土路基采用了片石气冷路基、热棒、片(碎)石护坡等主动保护多年冻土的工程措施,取得了很好的效果。但是,多年冻土区部分地段的路基工程从施工完成后到运营期均有一些病害产生,影响了行车速度和运营安全。因此,开展运营期多年冻土区路基工程状态的研究,是保证青藏铁路多年冻土区路基工程长期、安全、可靠运营的前提。本论文采用现场调查和观测、室内试验、理论分析和计算等方法,分析了影响青藏铁路冻土区路基工程状态的环境气温和冻土特征;通过对运营期多年冻土路基工程状态的现场调查和监测,研究了运营期多年冻土区路基工程状态的变化机理和影响因素;研究了不同环境地质条件的路基工程在其建设和运营不同阶段工程状态的变化特征;研究了保证路基工程状态符合运营条件的工程对策并进行了长期效果评价。通过本论文的研究,可以得出以下创新性结论:(1)冻土区路基工程状态包括以下三个方面的表现:路基力学状态:指明显表现出来的路基垂直方向变形(冻胀融沉变形)和水平方向变形(路基裂缝)以及由于这些变形引起的路基失稳现象;路基热学状态:指路基工程修建以后不同阶段路基地温场形态(土体不同部位温度变化);水热环境变化:指路基工程修建过程和运营过程周围冻土层上水、地表水变化及其侧向热侵蚀作用对路基变形和路基地温场的影响。(2)通过对青藏铁路开通运营以后包括建设过程中的路基工程状态分阶段的调查、观测和分析,对路基力学状态一路基变形和工程裂缝的发展过程以及对线路运营的影响进行了深入的研究,认为路基的热学状态是其发生发展的主导因素。改善路基力学状态应该从改善路基地温场形态出发,据此本文提出了相应的工程对策。(3)冻土区路基工程状态的变化与周围水热环境条件密切相关。在运营阶段周围水热环境条件在路基开裂的三个阶段:初期的裂纹和裂缝、中期的开裂和后期的裂开并滑塌起到诱发和拉动作用。(4)路基工程状态的变化机理内因在于填土的粘聚力和基底土体的压缩性,根本原因则是填土和基底土体地温场的不对称形态,后期发展则和外部水热环境影响有关。(5)有害路基工程状态的预防和整治,主要从抑制路基不对称形态地温场的工程措施为主,以保护路基周围水热环境为辅,在减少填土冻胀的前提下尽可能提高土体的粘聚力。(6)针对冻土区路基工程状态的最显现表现,即:路基变形及变形裂缝的变化机理和发展阶段,有的放矢的提出了针对不同阶段的工程对策:建设期间尽量采用改善填土颗粒级配和粘聚力的方法(土体分层加筋等),建设和运营期间采用冷却路基基底土体改善地温场形态的工程措施进行补强(片石护坡和热棒),防止路基坡脚积水和热融现象形成的工程措施(疏通路基坡脚纵向排水)。(7)对主要工程对策进行的数值计算模拟结果说明,防止裂缝和整治裂缝的关键在于控制冻融过程各个阶段的季节冻融速度和季节冻融土体厚度,减少路基中心和路基边缘部分的变形差异,降低融化季节路基本体产生的拉应力。(8)青藏铁路运营阶段对冻土区路基有害工程状态的整治和施工阶段的预防性整治不同,考虑既有路基工程病害整治的特殊情况,建议工程结构根据区域冻土条件和气候条件以及原有路基结构不同,可以选取各类热棒+片石护坡结构,片石护道补强结构、片石护坡补强结构等。(9)加强对路基工程状态的巡查,尤其是在融化季节初期的巡查监控,及时处理初期发现的有害工程状态(裂纹、积水等)是事半功倍的有效方法。本文研究过程的阶段性结论曾经在青藏铁路建设的各个阶段为工程补强设计和病害整治所采用,研究结论也被青藏铁路冻土区路基的运营过程所验证。更多还原

【Abstract】 The Golmud-Lhasa section of the Qinghai-Tibet railway （QTR） is 1,142 kilometers in length, of which 546.41 kilometers crosses large areas of continuous permafrost region （the talik region of the permafrost area is 101.68 kilometers）. The total distance of subgrade situated in permafrost region is 321.706 kilometers, accounting for 72.3% of the total length （about 444.73 kilometers） of subgrade region. Since QTR covers the permafrost section with more than 4,000 meters above sea level and the length of 965 kilometers or so, cold and oxygen lacking, permafrost and fragile ecosystem in the area are three major technical problems in QTR construction, and the permafrost ranks the top of the three in constructing and operating QTR. Therefore, as the saying goes that "The key to success or failure of QTR is subgrade, and the key to subgrade is permafrost". The whole project started on June 29^th, 2001 and opened for operation on July 1^st, 2006.With the purpose of protecting the permafrost effectively and maintaining the stability of subgrade engineering in the permafrost area, , aiming at permafrost subgrade, after positively protective measures of engineering, such as the crushed-rock subgrade, the two-phase closed thermosyphon subgrade, and the subgrade of crushed-rock slope protection, are taken in building the railway, the protective effect on the permafrost is obvious. However, during the completion and operation of the project, some diseases have been found at some sections in permafrost region, which affects train speed and safe operation. Therefore, studying on subgrade state in permafrost during QTR’ operation is a premise of assurance of its long-term, safe and reliable operation in permafrost region. The dissertation, by employing the methods of field survey and observation, laboratory test, theoretical analysis and calculation, will make an analysis of the surrounding temperature and permafrost character which affect state of subgrade engineering of QTR, explore the changing mechanism of the state of subgrade engineering in operation period through field investigation and monitoring of the state of subgrade engineering in permafrost region during operation period, examine the changing features of the state of subgrade engineering under different geological environment and in different stages of construction and operation and research on engineering countermeasure which can assure that state of subgrade engineering conform to OTR’s operation condition and make an evaluation about long-term effect. After the research on the state of subgrade engineering in the permafrost area during operation period of QTR, the innovative conclusions will be presented as follows:（1）The state of subgrade engineering includes the following manifestations in three aspects:Mechanical state of the subgrade: it means evident vertical deformation （deformation of frost heaving and thaw settlement） and horizontal deformation （crack in subgrade）, and phenomena of stability loss in subgrade resulted from the deformations.Thermal state of the subgrade: it means configuration of ground temperature field at different phases after QTR construction （temperature variations at different parts of soils）.The hydrothermal environmental changes: it means that changes in ambient suprapermafrost water and surface water, lateral heat erosion have an influence on subgrade deformation and ground temperature field during construction and operation.（2）By field investigation, observation and analysis of the state of subgrade engineering in different stages during QTR’s construction and operation , the subgrade mechanical state, are studyed, which includes the development process of subgrade deformation and engineering crack and the influence on the operation of QTR and the thermal state of the subgrade, as the dominant factor resulted in the subgrade mechanical state, are stated. Besides, corresponding countermeasures are put forward, for improving mechanical state of the subgrade should begin with the improvement of thermal state of the subgrade.（3）Changes in state of subgrade in permafrost region are closely related to the ambient hydrothermal environmental conditions. During operation period, ambient hydrothermal environmental conditions play a inducing and driving role in the three stages of crack in subgrade: cracks in earlier stage, fissuring in middle-term stage, and splitting and collapse in late stage.（4）The internal reason of changing mechanism of subgrade engineering state lies in cohesive strength of fill and compressibility of base soils, and the foundamental cause was asymmetric configuration of ground temperature field in fill and base soils. The latter evolving is related to the effect of outside hydrothermal environmental.（5）Engineering measurements of controlling asymmetric configuration of ground temperature field are the key method to prevent and improve the diseased subgrade engineering, with auxiliary protection of hydrothermal environment of surrounding, with cohesive strength of soils enhanced as far as possible at the precondition of deducing frost heaving.（6）Aiming at the most evident manifestation of state of subgrade engineering in permafrost—subgrade deformation and evolving mechanism and developing stages of cracks, engineering countermeasures for different stages are put forth definitely as follows, improving fill grain composition and cohesive strength （layered reinforcement in fill） during construction, strengthening subgrade with engineering measures of cooling base soils and improving ground temperature field configuration （crushed rock slope protection and two-phase closed thermosyphon） and taking the measures of prevention subgrade-toe from puddling and thermokarst phenomenon from forming （clearing out longitudinal drains beside subgrade toes）.（7）Numerical calculation results of major engineering countermeasures shows that the key to prevention and improvement of cracks in subgrade is to control seasonal freeze/thaw speed and thickness of freezing/thawing soils, reduce deformation difference of middle and marginal part in subgrade and decrease tensile strength generated by subgrade body during melting season.（8）During QTR operation period, since the improvement of diseased subgrade engineering state in permafrost region is different from protective improvement in construction stage, it was necessary to consider the specific conditions of disease control in subgrade engineering. It is suggested that the sorts of the thermosyphon combined with crushed rock slope protection structure, the crushed rock berm reinforcement structure, and the crushed rock slope protection reinforcement structure will be adopted, according to the differences of regional permafrost, climate conditions and original subgrade structure.（9）Reinforcing inspection of the subgrade engineering state—especially during earlier melting season, dealing with diseased engineering state in earlier stage in time is an effective method of getting twice the result with half the effort.During the process of the present study, phased conclusions have ever been adopted in engineering reinforcement design and disease control during every stages of QTR construction, and have benn also examined during long-term operation of Qinghai-Tibet railway in permafrost.更多还原