【作者】 许兰民；

【导师】 魏庆朝；

【作者基本信息】 北京交通大学 ， 道路与铁道工程， 2011， 博士

【摘要】 冻土区铁路的安全运营主要取决于冻土区主要工程即路基、桥梁、涵洞的稳定,这些工程的稳定则由其地基冻土的热稳定性所决定。冻土区路基工程施工对冻土带来的热扰动主要是填土热量消散和基底冻土散热界面改变带来的影响,对于低温冻土区路基基底冻土热稳定性的恢复,随着路堤高度的增加而延长,这种恢复过程对施工工序衔接及路基工程稳定都有一定影响。桥梁涵洞基础施工对冻土的热扰动问题则要比路基工程复杂许多。这不仅仅是施工活动对冻土扰动问题,更主要的是工程基础类型、施工工艺的特殊性对冻土产生的热扰动和热量消散是一个长期性问题,而且这些影响还会直接影响到基础稳定和施工工序的衔接等施工组织设计一系列问题。本文从施工区域冻土地质条件和冻土的热稳定性特征出发,研究分析了低温冻土区填土路基施工季节对路基基底多年冻土的热扰动,根据观测和计算结果,提出低温冻土区高路堤工程保证冻土热稳定性和路基稳定性的最佳施工季节和施工方法。根据青藏铁路建设过程对施工工期要求和五道梁地区施工对全线施工工期的控制和影响问题,作者通过现场混凝土灌注桩基础浇灌以后桩周地温场变化规律试验,混凝土浇灌工程中的水化热问题、混凝土入模温度问题对桩周土体回冻规律影响的数值模拟计算,解决了本地区桥梁基础灌注桩施工工艺和施工组织设计中的关键技术问题,保证了施工工序的顺利衔接和控制性工程施工工期,现场桩基试验和施工后3年的观测证明了桥梁基础的可靠性。本文针对五道梁地区气候和冻土热稳定性特征,还对涵洞基础型式提出了创新性改进。青藏铁路建设初期的暂行规范和过去经验,认为冻土区涵洞基础推广型式是预制拼装式基础,作者根据目前施工机具、施工技术、施工能力的现状和五道梁地区气候特征,提出局部地区采用现浇混凝土整体式基础的型式。通过现场施工验证,计算机数值模拟和施工工序衔接特征,作者认为,只要对开挖涵洞基础土体采用局部遮阳措施,基础底部铺设6cm厚度的保温材料,这种整体式现浇混凝土基础对基底多年冻土的热扰动在1—2各年际冻融循环过程即可消散,不会对涵洞基底多年冻土和基础本身的稳定性造成危害,而且这种基础型式涵洞基底不易渗水,中间不留缝隙,减少了运营过程涵洞基底冻胀的发生,保证了其使用寿命和稳定性。本文紧密结合生产实践进行科学试验和理论计算,对五道梁低温冻土区高路堤工程和桥梁桩基以及涵洞基础施工工艺的研究,建立在对五道梁低温冻土区冻土热稳定性特征及其变化规律深刻认识的基础之上,研究结果对青藏铁路冻土区工程建设具有理论和工程实践意义,主要表现在：混凝土入模温度在融化季节无法保证原来规范规定的较低的入模温度,经过对混凝土水化热对冻土热扰动影响计算和对混凝土添加剂成分的合理配比试验,混凝土入模温度在融化季节最高可以容许到12℃。现浇整体式涵洞基础基底换填和铺设一定厚度保温材料,可以有效的控制对基底多年冻土热扰动,使其尽快恢复稳定的热状态,保证基底稳定。因此,针对不同气候特点和冻土热稳定性特征,采用合适的施工工艺,可以应用现浇整体式涵洞基础。桥梁灌注桩基础施工中,混凝土入模温度和桩周土体回冻是控制性施工工艺,桩周土体回冻标准应该包括两部分概念,一个是适合施工工序衔接的回冻标准,二是达到桩基设计承载力的回冻标准。通过试验确定这两种标准,既能够标准桩基设计承载力,又恰当的利用了桩周土体回冻规律,衔接后续工序,提高施工效率,科学合理的安排施工工期。根据现场试验,施工建设期间和运营初期观测数据和建立在现场实测数据基础上的计算机数值模拟结果,说明根据上述工艺进行的桥梁涵洞基础施工其工程效果和初期工程效果是安全可靠的。更多还原

【Abstract】 The safety in operation of railroad in permafrost area depends primarily on the stability of the main constructions, which include subgrade, bridge and culvert. The stability of constructions is determined by the thermal stability of the frozen soil foundation. The thermal disturbance brought by embankment engineering construction in permafrost area mainly includes the dissipation of fillings’ heat and the influence from changes of permafrost radiating interface in the subgrade base. As for the thermal stability recovery of permafrost at subgrade base in low temperature permafrost area, the time increases with the height of the subgrade. This recovery process affects the joints in working operations, as well as the stability of subgrade engineering. The problems of thermal disturbance to permafrost caused by constructions of bridges and culvert foundations are much more complicated than subgrade engineering. The problems are not only about the disturbance of constructions to the permafrost, but more importantly, the thermal disturbance and heat dissipation caused by the particularity of types of foundations and working operations are longstanding problems, which directly affect a series of problems including foundation stability and joints in working operations.Based on the regional permafrost geology and characters of thermal stability, this text studies the thermal disturbance on the permafrost in embankment subgrade base from earth embankment height and construction seasons in low temperature permafrost area. According to the observed and computational results, the best construction seasons and construction methods are proposed to ensure the thermal stability of permafrost and embankment stability of high embankment constructions in the low temperature permafrost area.Considering the construction duration of Qinghai-Tibet Railroad and the control and influence of constructions in the Wudaoliang area on the whole line’s construction period, the variation of ground temperature field at pile sides after the casting of cement caisson piles was tested, along with the heat of hydration during concrete casting. Numerical simulations about the influence of concrete molding temperature on the refreezing of soil at pile sides were conducted. Therefore, the key technological problems in working operations and construction organization design of local bridge foundation caisson pile constructions were solved. The smooth joints in working operations and the construction duration of controlling constructions were ensured. The stability of bridge foundations was attested by the in-site experiments and the monitoring after construction for three years.In the light of the characters of climate and thermal stability of permafrost in Wudaoling area, innovative improvements were proposed on the types of culvert foundation. The temporal standards during the initial construction period of Qinghai-Tibet Railroad and the past experiences believed that the promotion type of culvert foundation in permafrost area was prefabricated assembly foundation. Based on the construction tools, construction technology and construction capacity at the present state and the climate characters of Wudaoliang area, the idea that cast-in-site concrete monolithic foundation should be used locally is proposed. Through in-site construction test, computational simulation and the characters of joints in working operations, the author found that if local shading and heat insulator with a depth of 6cm were employed, the thermal disturbance on the permafrost at subgrade base from the cast-in-site concrete monolithic foundation would be dissipated within one to two years of freezing and thawing cycle, which would not bring about damage to the permafrost at culvert foundation base and the stability of the foundation itself. Moreover, water creep is rare for culverts with this type of foundation. The absence of joints also reduces frost heaving during operation, which enhances service life and stability.With scientific experiments and theoretical calculations closely related to production practice, the working operations of high embankment constructions, bridge pile and culvert foundations in Wudaoliang low temperature permafrost area were studied, based on the characters and variations of permafrost thermal stability in Wudaoliang low temperature permafrost area. The results have theoretical and practical significance on the constructions in the permafrost areas at Qinghai-Tibet railroad, and they are:The high concrete molding temperature during thawing seasons could not meet the original standards. Through calculations about the influence of concrete heat of hydration on the permafrost thermal disturbance and the mixture ratio experiments of cement addition agents, the acceptable value of molding temperature during thawing seasons can be up to 12℃.The thermal disturbance of permafrost at foundation base can be effectively controlled by the replacement of foundation base of cast-in-site concrete monolithic culvert foundations, along with the laying of insulating materials with a certain depth, which will facilitate the recovery of stable thermal state while maintaining the stability of foundation base. Therefore, with different climate and permafrost thermal stability characters, suitable construction technologies should be employed, and cast-in-site concrete monolithic foundations can be adopted.As for the construction of bridge caisson piles, concrete molding temperature and refreezing of soil at pile sides are the controlling operations. The standards of refreezing of soil at pile sides consist of two concepts, one is the refreezing standards suitable for the joints in the working operations, and another one is the refreezing standards meeting the designed capacity of pile foundations. These two standards are acquired through experiments, thus the capacity of pile foundations can be standardized while the law of soil refreezing at pile sides can be employed. The proceeding procedures are connected, the efficiency of construction is improved and the duration of construction can be scientifically and reasonably arranged.Trough in-site tests, observed data during construction and initial operation periods and numerical simulation results based on the in-site observed data, the bridge and culvert foundation constructions and the initial project results following the above-mentioned construction technologies were proved to be safe and reliable.更多还原