| Frost heave and thaw settlement are the most common engineering disasters during the construction of railway and highway in frozen soil area,meanwhile,the pile foundation of bridge engineering in frozen soil area is also faced with the above two problems.In order to provide the guarantee for the safety and long-term use of the project in frozen soil area,we should carry out the research on the thermal-mechanical coupling of the pile-soil system on the slope,comprehensively understand the distribution of the temperature field and the frost heave characteristics of the soil around the pile,the freeze pulling and stress forms of the pile on the slope,and the frost heave characteristics of the pile-soil interface.Using the finite element software ANSYS,a three-dimensional thermo-mechanical coupling numerical model of pile-soil system on slope is established.The change of temperature field around pile,the frost heave deformation of pile and soil at pile-soil interface,the stress form of pile foundation and the mechanism of anti-freeze pulling resistance are studied.The main conclusions are as follows:(1)The temperature of soil within 3 meters from the ground fluctuates greatly with the change of external temperature.Under the influence of climate warming and solar radiation and other factors,the heat absorbed by the pile foundation is transferred to the frozen soil layer,so that the temperature of the soil around the pile is higher than that far away from the pile foundation at the same depth.The influence of external temperature on soil temperature will decrease with the increase of soil depth.When the soil reaches a certain depth,the temperature of the soil is no longer affected by the external temperature.(2)Due to the uneven frost heave of the soil at the pile-soil interface of the slope,the horizontal displacement of the pile sliding along the slope is generated.The calculation the following three angles as 15°,30°,45°of the slope,the results show that the larger the slope is,the greater the horizontal displacement of the pile sliding along the slope is.The vertical displacement of the pile will be generated when the soil frost heaves,and numerical simulation of four different buried depths as 8m,12 m,16m,20 m of pile foundation,the results show that the shallower the buried depth is,the larger the vertical displacement is.(3)The relative sliding displacement between pile-soil interface is the largest within 3m below the ground surface.With the decrease of soil temperature,the displacement of pile body changes slowly,but the frost heave of soil around pile body increases continuously,resulting in the increase of relative displacement of pile-soil.With the decrease of ground temperature,the frost heave becomes more and more severe,and the tangential frost heave force increases,which leads to the increase of vertical displacement of pile foundation.In the process of frost heaving,the critical points of the positive and negative values of thetangential frost heaving force between the pile-soil interface gradually move downward.The pile foundation on the slope is not only bear the tangential frost heaving force,but also the horizontal frost heaving force.Its maximum value appears on the surface.With the deepening of the depth,the horizontal frost heaving force decreases gradually.(4)From December to February of the next year,the axial force on the pile body is positive,and the positive value indicates of the tension of the pile foundation.The axial force increases with the decrease of temperature.The temperature in January is the lowest,and the axial force is the largest at this time,and the maximum axial force appears near the surface of the earth;With the increase of the depth of pile foundation the axial force decreases.According to the axial diagram,the maximum tensile stress of the pile body is less than the tensile strength of the pile material,so the pile foundation will not be broken and is in the safe stage. |
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