【作者】 朱秋颖；

【导师】 王旭；

【作者基本信息】 兰州交通大学 ， 道路与铁道工程， 2011， 硕士

【摘要】 多年冻土在我国分布广阔,作为一种特殊地基,它所产生的工程病害造成工程失效,甚至破坏,在国内外工程界引起广泛重视,因此研究多年冻土具有重要的意义。本文在国内外冻土地基中桩的模型试验的基础上,以相似理论为基础,对模型试验方案进行了设计。模型桩材料分为铝管和木质,模型桩形式分为单桩和异形“T”型桩。作者利用本校的低温环境箱制作了低温模型试验箱,同时进行了模型桩的制作以应变片的粘贴,测温元件与位移百分表的布置,并对模型试验所用土进行土工试验,测定土的物理力学参数。准备工作完成之后,通过模型试验模拟冻融循环下冻土中桩的冻拔现象,探讨经过2个季节循环后桩身内力以及桩的变形,在其他研究学者对冻土一桩研究的基础上,结合试验所测数据与现有理论,对温度的变化规律,桩在冻融循环作用下冻结力随时间、深度的变化规律进行分析,同时计算得出土与桩的变形量,为多年冻土桩基础设计提供参考。得到以下研究成果：(1)经改良后的冻土模型箱能够有效地实现土体的冻结与融化过程,可模拟出多年冻土区冻融循环过程。(2)无外界水补给的条件下,温度是影响冻结力最主要的因素。在冻结过程初期,温度呈直线下降趋势。温度由上至下传递过程中存在温度梯度,随着深度的增加,土体对温度的敏感程度降低。(3)冻结力与深度的变化曲线呈“抛物线”形,极大值发生在1/3-1/2桩深范围内。之后,随着深度的增加,冻结力逐渐减小。由于桩底温度受外界影响较小,桩的下部冻结力变化幅度较小。同时,冻结力随时间的变化产生衰减现象,这与冻土的蠕变性质有一定关系。相同试验条件、同种材质、同一时间以及同一深度条件下,“T”型桩的冻结力大于单桩的冻结力,这是由于“T”型桩的桩顶扩大段会产生一定的法向冻胀力,因此增大了切向冻结力。(5)冻融循环过程中桩周土位移变化量大于各类型桩顶位移量。随着温度的降低,桩周土冻胀隆起,各类型桩有上拔趋势；随着温度的升高,桩周土融沉下陷,各类型桩有下沉趋势。土体最大冻胀与融沉量分别为2.65mm和4.66mm；桩体最大上拔量为1.54mm,最大融沉量为1.19mm,分别占桩长的0.51%和0.4%。更多还原

【Abstract】 China is a large country with lots of permafrost regions. As a kind of particular subsoil, the permafrost damage which causes engineering failure, even destroyed. It already becomes the important subject that the domestic and international project circle has paid close attention to these problem, so studying the permafrost is of great significance. In this paper, according to the pile model test in the frozen soil foundation at home and abroad, based on the similar theory, designing the plan of model test. There’re two kinds of materials of model pile, including aluminum pipe and timber pile, there’re also two kinds of cross section shape of model pile, including single pile and T-shaped pile.Utilize the environment box at low temperature in this school and manufacture the model box and piles, paste the strain slice and arrange the temperature element and dial indicator. Meanwhile, do geotechnical test for soil which is needed in model test to determine the soil’s physical and mechanical parameter. After it, start to do model test to simulate the frost heaving phenomenon respectively under the freeze-thaw cycle conditions, discuss the internal stress and deformation of pile which is after two seasons’ freeze-thaw cycle. Based on the theory of permafrost-pile studied by other scholars and combined with the test, I draw the conclusion about variation of temperature and temperature gradient, the changing of frost heaving with time and depth under the freeze-thaw cycle, and the frost heaving amount of soil and pile. providing the reference for pile’s designing in permafrost. Finally, according to the test, we obtain results as following aspects,(1)The modified permafrost model box can effectively achieve the process of freezing and thawing, the freeze-thaw cycle in permafrost is well simulated with it.(2)Without the external water, temperature is the most important factor which is affecting the freezing force. At the beginning of the freezing process, the temperature presents the linear decrease tendency. Temperature transfer from top to bottom, in this process, existing a temperature gradient. With the increasing of depth, the thermo-sensitivity of soil decreases.(3) The changing curves of freezing force and depth show a parabola type, the maximum occurred in the range of 1/3～1/2 depth of pile. Then, with the increasing of depth, the freezing force decreases. And the variation range of freezing force which is at the pile bottom is small, because pile bottom has little effect on the temperature. The freezing force with the change of time will lead to a phenomenon of attenuation, because it is related to the creep property of permafrost.(4)Under the condition of the same experimental environment and material, same time and same depth, the freezing force of T-shaped pile is larger than the single pile, the normal frost heaving force exists on the expansion section of pile top, it increases the tangential frost heaving force.(5)In the process of freeze-thaw cycle, the displacement of soil and the pile end presents a spiral decent tendency. With the decreasing of temperature, the water in the soil porosity transform to the ice, the soil occur frost heaving deformation and the pile pulls out. With the increasing of temperature, the ice which has the cementation transform to the water, the soil occur thaw deformation and the pile sinks. The maximum frost heaving and thaw quantity of soil are 2.65mm and 4.66mm. The maximum frost heaving and thaw quantity of pile are 1.54mm and 1.19mm, the ratio of the length of pile is 0.51% and 0.4%.更多还原