Development Of The Bearing Capacity Of Cast-in-place Piles In Permafrost Regions During The Early Construction Stage

Bored piles is widely used for its advantages of convenient construction, high bearingcapacity and strong anti-freeze ability, however, these elements, the disturbance of drillingholes(caused by its frictional heat and slurry caloricity),the sensible heat mould carried bypile foundation concrete and the heat of hydration bring a lot of thermal disturbance to thefrozen soil around the pile, breaking the balance of original of the frozen soil structure,causing the decreasing of the permafrost’s frozen strength even melting, even futureresulting in the lowing of pile foundation’s bearing capacity. Meanwhile, the formation anddevelopmental change of bearing capacity of pile foundation in permafrost area have thedirect relationship with the temperature condition and change process of the pile, and after acertain period of time, with the temperature field of pile balancing once more, bearingcapacity of pile foundation gradually formed.First of all, this paper makes the finite element modeling to the process of hydrationheat of cement, taking the overall consideration to the effect that the time history andreaction temperature have on the hydration heat rate, bringing about the adiabatictemperature rising model of concrete which is considering the hydration degree,additionally, on these basis, it gets the numerical simulation to bored piles and temperaturefiled of permafrost surrounding piles to analyze the regulation about the temperature ofintercontact surface between pile and soil changing with the variational regulation both intime and the radius of the unfrozen soil around the pile under the different conditions offrozen soil. At the same time, this paper also introduced the prediction about the concrete’searly strength basing on the mature stage theory and three common function models used toexplain the mature stage theory. At first, the function relationship between mature stage andconcrete strength is fitted with the lab experiment, then the effectiveness of the proposedfunction is assessed by making use of the practical engineering,which has achieved goodresults. In addition, it makes prediction to the bearing capacity of pile foundation in earlyrefreezing period and introduces the forming process and characters of the bearing capacityof bored pile in the ever–frozen soli area as well as the way to count the perpendicularbearing capacity of pile foundation in the early refreezing period of the unfrozen soil and the time of refreezing.Generally get the conclusions as following:(1)The adiabatic temperature rising modelof concrete which is considering the hydration degree can describe the hydration heatprocess of concrete more exactly.(2)For different types of frozen soil, the temperature ofintercontact surface between pile and soil will change with the variational regulation both intime and the radius of the unfrozen soil around the pile.(3) Put forward the predictionmethord about the concrete strength of pile foundation in early refreezing period inpermafrost areas,and arrange the time reasonable of load application to pile, and it has acertain theoretical and practical value to construct the pile foundation in the ever–frozenground area.