高纬度岛状多年冻土桥梁桩基回冻前后承载力的研究

发布时间：2018-06-15 08:02

  本文选题：岛状多年冻土 + 桥梁桩基础　； 参考：《东北林业大学》2015年博士论文

【摘要】：多年冻土与普通的土体相比具有独特的工程性质,冻土地区的桩基础施工后桩身及周围土体在冻土地温作用下逐渐回冻,回冻过程中桩与周围土体逐渐联结成一个整体共同承受外荷载作用。由于以上现象在进行多年冻土地区桥梁桩基设计时也产生了一些难题,比如桩基的回冻时间及回冻前后桩侧摩阻力变化规律尚不明确,承载力计算时冻土层中的摩阻力的取值缺乏依据等等。因此,为了准确掌岛状多年冻土地区桥梁钻孔灌注桩的回冻时间、桩基回冻前后承载力的变化,在岛状多年冻土地区选择2个试验地点,每个试验地点浇筑3根15 m长的试验桩,并在试验桩处布设温度监测系统,采集桩基回冻过程中的温度数据,根据温度监测结果判断桩基回冻状态,在桩基完成回冻前后分别进行静载与动测试验,分析回冻前后桩基承载力、各土(岩)层的侧摩阻力及桩端阻力的变化规律。监测及试验结果表明：桥梁钻孔灌注桩浇筑完成后,在水化热、冻土地温的耦合作用下桩基温度呈现动态变化,桩基回冻后冻土上限以下的温度趋近于所在区域的冻土地温,试验桩所在区域岛状多年冻土地温约为-1.9℃,桩基完成回冻后桩身内部温度与桩侧lm处的土体温度变化趋势相同,相同深度处的温差小于0.1℃；桩基回冻后的承载力约为回冻前承载力的1.45倍、2个试验地点处试验桩桩端阻力平均增幅为45.8%、回冻后各土(岩)层的桩侧摩阻力也都有所增加,其中块石夹土增加幅度为75%、岩层增加幅度在30%-46%之间、圆砾与土按不同比例组成的土层增加幅度在30%-70%,2个试验地点冻土上限以下各(岩)土平均增长率分别为49.6%和41.7%；用静载法实测出的各土层回冻前后的桩侧摩阻力值修正高应变动测法桩-土力学模型中的土层参数,计算曲线与实测曲线拟合较好,动测与静载试验所得到的桩基极限承载力误差为3.78%,试验结果相符合。本研究可为类似冻土条件下的桩基设计及承载力检测提供理论依据。
[Abstract]:Permafrost has a unique engineering property compared with ordinary soil. The pile body and surrounding soil in frozen soil area are gradually frozen under the action of frozen soil temperature after the pile foundation is constructed. In the process of refreezing, the pile and the surrounding soil gradually joined together to bear the external load together. As a result of the above phenomenon in the design of bridge pile foundation in permafrost region, some difficulties have arisen, such as the freezing time of pile foundation and the variation law of pile side friction before and after refreezing. In the calculation of bearing capacity, the value of frictional resistance in frozen soil is lack of basis and so on. Therefore, in order to accurately control the refreezing time of bridge bored pile in the island permafrost region and the change of bearing capacity of pile foundation before and after refreezing, two test sites were selected in the island permafrost region. At each test site, three test piles with a length of 15 m were built, and a temperature monitoring system was set up at the test piles to collect the temperature data during the freezing process of the pile foundation, and to judge the refreezing state of the pile foundation according to the results of temperature monitoring. The static load test and dynamic test were carried out before and after the freezing of the pile foundation, and the variation rules of bearing capacity, lateral friction and pile tip resistance of each soil (rock) layer before and after refreezing were analyzed. The results of monitoring and test show that the temperature of pile foundation changes dynamically under the coupling action of hydration heat and frozen earth temperature, and the temperature below the upper limit of frozen soil after the pile foundation is frozen is approaching to the frozen soil temperature of the region after the bridge bored cast-in-place pile is completed, and the results show that the pile foundation temperature changes dynamically under the coupling action of hydration heat and frozen soil temperature. The soil temperature of the island permafrost is about -1.9 鈩，

本文编号：2021320