Experimental Research On Long-term Plie Capacity Features With Different Construction Method In Frozen Silt Soil Ground

More and more structures are needed to build in permafrost regions for western development of our country, and in order to protect the stability of the permafrost foundation, pile foundation becomes one of the most appropriate form that designing according to the principle of "protecting permafrost". In permafrost regions, frost heaving and long-term bearing capacity is usually insufficient in the process of using pile foundation, which can lead to project failure. So there is very important meaning for researching the long-term bearing characteristics of piles.This paper firstly introduces the research status at home and abroad of bearing characteristics in permafrost regions, the effect of hydration heat to the pile foundation engineering and different ways of making pile to load-bearing characteristics, and then the research content and methods are confirmed.Then the effect on different ways of pile to long-term bearing characteristics in frozen silt is researched by using the indoor model test,the model box in low-temperature laboratory of Lanzhou Jiaotong university is used to place the four concrete piles that have the same diameter and length,and different ways are adopted to make pile.They are bored pile, compresol pile with prepared hole, inserted pile and driven pile with prepared hole, respectively. The filled silt is freezed to the setting temperature of-1.0℃, then the four piles are made by ways of fore-metioned. When the temperature around bored piles return to 95% of the initial value, the four piles are loaded by using hydraulic jack and pressure dividing valve. Electromechanical dialgauge of WDB-30 is placed on the top of the pile, deformational values of foil gage around piles and displacement values on the top of piles are collected by static strain tester of NV2312 N. At the same time, temperature inspecting instrument is used to record temperature’s changed value of each layer to get the effect about hydration heat of concrete to filled silt around piles. The different influences on pile forming process to displacement of pile top, axial force around pile, freezing friction and resistance at the bottom of pile are obtained by analyzing the collected testing datas. The rheological curve is made by the curve of load- settlement for each pile, the load when the steady sinking speed on pile top tends to zero can be thought as a long-term bearing capacity of pile. The estimated long-term bearing capacity of bored pile and compresol pile with prepared hole is geted by the mentioned measures, and they are all around 6 kN, the estimated long-term bearing capacity of bored pile is slightly bigger than compresol pile with prepared hole. The estimated long-term bearing capacity of driven pile and inserted pile with prepared hole are around 4.5kN and 3.5kN respectively. So under the different ways of pile, the density of backfill materials around inserted pile is not easy to control, that make its bearing capacity is low. For the bored pile and driven pile with the same loading, their bearing capacity are similar and the bored pile is slightly larger than the driven pile, at the same time, the construction equipment of driven pile is demanded higher and construction technology is controlled badly, therefore bored piles is used widely in permafrost region.Finally, FLAC3 D is used to the test process and the three different ways of making pile respectively are used to numerical simulation, the effect of construction technology in frozen silt to the long-term bearing characteristics for piles is analysed comprehensively by establishing static- temperature field coupling.The results that satisfied the similarity theory are aquried by comparing the the numerical results with the results of indoor model test, and it has a guiding role to the foundation construction in frozen pile.