Model Experimental Study And Thermal Analysis On Bored Pile In Permafrost Region

Frozen soil is a special kind of soil, besides that the water content, density and mineralcomposition will affect its engineering properties, physical and chemical properties, it is verysensitive to the change of climate and environment. The bearing capacity of pile foundation infrozen soil is seriously influenced by the temperature state, when the temperature of frozenfoundation increases, the bearing capacity and freezing strength will decrease.In engineering construction of permafrost areas, bored pile is one of the most commonconstruction methods of pile foundation, because it has a small impact on the heat of frozensoil, it can maintain the original state of frozen soil. In addition, the construction method ofpile is simple, and the pile has a high bearing capacity and frost resistance after completion,so bored pile has been widely used and developed in permafrost region.Usually, because of the physical and chemical reaction occurred between cement andwater, concrete pile will release hydration heat after it is casted, as for the bored pile inpermafrost region, the heat caused by drilling and released from the concrete pile will bringthermal effect to frozen foundation, and the hydration heat of concrete is the main source, theheat is gradually transferred to soil around pile in refreezing process of frozen soil, whichchanges the original state of temperature field in frozen soil. Especially because the hydrationheat released from bored pile deeply affect the temperature field of soil, resulting in theincreasing of temperature of soil around pile, the soil will stay a non frozen state in a shorttime. However, the bearing capacity of pile is seriously restricted by temperature field of thesoil around pile in permafrost region, so research on the refreezing process of soil around pilein permafrost area has important guiding significance for design and construction ofengineering in permafrost area, and also provides a reliable basis for the understanding offormation of bearing capacity of pile and construction of follow-up projects.Because of the special nature of frozen soil, field test of pile in frozen foundation takes along time, and needs a lot of manpower, material and financial resources, therefore, the best solution to replace field test is conducting indoor refreezing test of frozen soil. In this paper,by using testing instruments of self-made precast concrete pile (with built-in electric rods),self cooling coil, temperature detector, temperature sensor, DC power and XT5405typehigh-low temperature freezing-thawing cycle test chamber, to consist a set offreezing-thawing and refreezing testing device, the device is used to simulate the freezingprocess of bored pile in permafrost region, and study the refreezing rules of soil around pileunder conditions of different hydration heat and ground temperature.In addition, finite element software ANSYS is used to simulate the temperature field ofrefreezing process in the indoor test. Based on the influence of hydration heat of concrete pile,given differential control equation and boundary condition is used as a precondition tosimulate the thermal disturbance and refreezing process of indoor model test. After analyzingthe results of numerical calculation, the changing rule of temperature of soil around pile withtime and depth can be exactly obtained.In this paper, through different research methods, some valuable data and conclusions areobtained, which provides a good reference for the study on the refreezing process of soilaround the pile in permafrost area.