Experimental Research On Freezing Strength And Negative Friction Of Pile Side In Permafrost Region

With the development of infrastructure in permafrost regions, Pile foundation is widely used because of its thermal stability and other advantages. However, because the properties of permafrost seriously varies with the change of temperature, freezing and thawing damage of pile occurs frequently in permafrost region, and the primary reason of freezing and thawing damage is that the interaction between pile and soil is extremely unstable due to the heterogeneous freezing and thawing of permafrost. In order to find out the interaction mechanism between pile and soil and prevent the damage economically and environmentally, research on the friction force caused by thawing and freeze strength between pile and soil has been carried out. This project is supported by the 220kV Table-Mohe new construction of transmission lines, and the soil samples are taken from Mohe.According to the characteristics of temperature instability of frozen soil, the concept of freezing intensity and the mechanism of the friction force in the frozen, referring to other similar experiments, flexible usage of test equipment, the test apparatus of frozen strength and frictional resistance were developed. There are two laboratory experiments in this thesis: Freeze Strength Test and Negative Friction of Pile Test.â'ˆFreeze Strength TestThis test mainly focuses on the influence of water content and freezing temperature on freezing strength, and 54 tests were carried out on the soil taken from No.â‘¡1 andâ‘¡soil layers at engineering filed in Mohe. It can be obtained from test data that freezing strength and residual freezing strength are linearly increase with the decrease of freezing temperature, and both vary with the change of water content of permafrost; further more, there is a water content limit, and when water content of permafrost is less than it, freezing strength and residual freezing strength increase with increment of water content, but when water content is more than it, freezing strength and residual freezing strength both decrease with increment of water content.â'‰Test for Negative Friction of Pile in Frozen SoilNegative Friction of Pile Test concentrates on the influence of water content on thawing settlement displacement of soil and negative friction of pile and soil, and in closed system, 6 tests were performed on the soil taken from No.â‘¡1 soil layer at engineering filed in Mohe. Therefore, these experimental results were found, as following: in the process of thawing of frozen soil, the temperature, displacement and negative friction of pile and soil develop in three stages, but the changes of the three stages lag to the thawing time. The amount of thawing settlement of frozen soil increases with the increment of water content, but negative friction decreases with the increment of water content.To compensate the limited measuring points of tests and the interference caused by the test equipment, the finite element software ABAQUS is used to calculate the temperature field and the settlement of frozen soil in the negative friction of pile in the frozen soil, and then, the amount of thawing settlement and soil temperature are obtained at every moment in the calculation model, and the same conclusion was achieved as test results.