Research On The Analysis Thermodynamics Of Cast-in Place Pile In High-temperature Permafrost And Pile Model Test In Frozen Soil

Solid ice is excited in permafrost, solid ice and liquid water can be converted to one another with the change in temperature which forms the complicated permafrost foundation. According for the principle of protecting the permafrost, the pile foundation's disturbance to the subsoil's temperature field is smaller in permafrost regions, and the pile foundation has the advantage of high carrying capacity, strong frost resistant and simple construction. As for these above, so it is fitted to the permanent building foundation in permafrost regions.There are many methods for construction of cast-in-place pile in permafrost, every method will disturb and bring some heat to the natural permafrost foundations, especially after pouring concrete because of the role of hydration. These heat will change the natural temperature field result that the frozen ground become as thawed soil, then the bearing capacity is gradually grown down. The refreezing process after pouring concrete is a heat exchanging process between the concrete and the foundation soil. The reducing of the concrete's hydration heat and absorpted by the subsoil from the pile wall reduce the piles' temperature down, and the piles' temperature is gradually grown down. The temperature get balance between piles and soil. After a period of time, the bearing capacity gradually forms as the subsorl recovers the freeze state.Due to the special properties of the permafrost, such as strong rheological properties: long in-situ test cycle; unfavorable control and costly boundary conditions. It is necessary to carry out indoors permafrost simulation experiment to study pile foundation permafrost bearing behavior.According to the effective method of studying the characteristics,the test can provide the necessary data and experience for engineering design and construction through control and change boundary conditions under different conditions. To present by indoors pile static load model test, this paper shows as follows:the freezing stages of soil under different temperature with time,and analysis the process of soil freezing.By the means of single pile on the indoor tatic load model test, we obtain a series of experiment datas, and draw the curve of tangential frost heaving force with depth. When the temperature maintains a stability in a certain range, we obtain the pile body curve axial force under different load, the frozen force curve with depth.The temperature field for the refreezing process of pouring concrete about the trial lot in Qing Shuihe QingZhang Railway which is imitated using the numerical analysis method by ANSYS finite element analysis software. Considering the influence of concrete hydration heat, the temperature field calculation model is build to do thermodynamics ansysis between pile and soil, get the the thermo-integrator of refreezing process and obtain the change of temperature with time at the different depth; In giving field temperature conditions, the coupling calculation and analysis between temperature field and stress field are conducted to obtain the rule between the frozen force and depth. The results of this paper can provide beneficial reference for project of cast-in-place pile in high temperature permafrost foundation.