Experimental Study Of Single Pile Frost Heaving Cycle In Permafrost

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%.