| Our country is the third largest permafrost country in the world, and the permafrost area is about2.15x106km2, occupying about22%of the land area. It is particularly important that solving the problem of structure foundation when building structure in permafrost area. Now, CFG technology is widely applied in the complex soil foundation. The main characteristic is the widely adapted, rigid pile clearly, some drainage and time effect, and the less deformation. The much more characteristic of CFG composite foundation is fully made up the shortcomings of the permafrost, giving a new choice to the building foundation problems which is how to deal with the permafrost. Compared with the Tibetan permafrost, the island permafrost are more susceptible to the influence of thermal disturbance, but at present our country is without a systematic and quantitative research about the temperature field distribution of the CFG composite foundation and island permafrost.In view of the research status about the CFG composite foundation and island permafrost temperature field, basing on the YiSui highway actual projects, the test ground is built at the island permafrost area, and observing the temperature for a long time. Analyse the temperature change rule of the island permafrost and the CFG composite foundation after concreting. The atmosphere temperature change is also observaed for analyzing the temperature change situation about raft. The island permafrost temperature is analyzed after constructing the subgrade. On the basis of experimental data, the CFG composite foundation is analysed with finite element software ABAQUS to determin the thermal disturbance range in the island permafrost, as well as the different roadbed height how to effect the island permafrost temperature, and analyzing the different factor how to influence the temperature changing rate of the island permafrost, the main research and the research results are as follows:(1) Basing on the YiSui highway actual projects, the test ground is built at the island permafrost area. The testing includes three parts which are the CFG simple pile, the CFG composite foundation roadbed and the CFG composite foundation culvert. Observe the permafrost temperature for a long time.(2) In the CFG simple pile testing, by observing the temperature changing of the CFG pile and the permafrost after concreting, it is founded that the temperature disturbance of the island permafrost from the CFG simple pile is much weak, and because of the surface soil is exchange-fill by the gravel soil, the insulating layer, which thickness is0.8m, has been formed in the soil inside.(3) In the CFG composite foundation testing about roadbed and the culvert, by observing the temperature of the CFG composite foundation and the raft, it is found that be because of the fly ash concrete hydration heat is small after concreting the CFG composite foundation, the CFG pile has no heating process as well as being always in the condition of cooling after casting, and there are two temperature reducing inflection point at the time of half an hour and24hours after casting.At the same time, on analyzing the temperature changing of the raft and the atmosphere, it is concluded that the atmospheric temperature is the main influencing factors to the raft temperature. Howover, the raft contacts with the atmosphere directly, then the temperature fluctuations at the upper is larger than the cross section. The temperature variation curve of the lower section is relatively smooth, no large fluctuations.(4) By analyzing the temperature field of the island permafrost beside the CFG pile, the CFG composite foundation weakly effect the soil far away1.5times pile diameter from the pile side. However, the roadbed has a great influence to the island permafrost temperature disturbance. After the subgrading the island permafrost temperature increases significantly, and with the deepness of soil deepen, the soil temperature amplitude is decreasing. As the culvert test area didn’t doing the subgrade, so in the the culvert area the permafrost temperature has little change.(5) Using the finite element software ABAQUS to simulate and analyze the temperature testing, by comparing with experimental data, it is found that this method, which is used to establish the model for analyzing the island permafrost temperature field, is correct. By the simulation analysis, it is found that the island permafrost temperature perturbation range is1-1.5times the pile diameter, effected by CFG composite foundation with different pile diameter, while the pile length has little influence on the island permafrost temperature.(6) By analyzing the island permafrost beside the CFG pile with different pile spacing and pile diameter, when the pile spacing and the distance from the selected soil temperature points to the pile side are all based on the pile diameter multiple, whatever how the pile diameter change, when the pile spacing is the same multiple of the pile diameter, then the temperature of permafrost, where distance the pile side is the same multiple of the pile diameter, is the same too, and simulate and analyzing raft temperature variations with28days after concreting.(7) By numerical simulating the roadbed and the island permafrost, analyse the different roadbed height how to effect the permafrost temperature, and obtain that when the roadbed is in building the height of roadbed is proportional to the permafrost temperature rising. The greater the permafrost roadbed height, the higher temperature rising. After be calculated, at the place under the surface of6m the permafrost temperature disturbance by roadbed is much little, and the temperature changing range is from0.4℃to1.2℃no matter how the roadbed height change.(8) With the different roadbed height, simulate and calculate the annual temperature changing of island permafrost under the action of atmospheric thermal cycle, and then obtain that the roadbed height is inversely proportional to the permafrost temperature. The higher the roadbed height is, the little the permafrost temperature, and the shorter the melt time is. The roadbed height has a cut-off point for5m, and when the roadbed height is higher than5m. the melt time of permafrost which is under surface6m will reduce significantly, and the temperature will no longer change while the roadbed height change again. By calculation, find that after paving asphalt pavement, there is15to20days in advance about the melting of the permafrost period, and freeze later for13to15days. The maximum and the minimum temperature of permafrost in a year is also change accordingly.(9) Finaly. calculate the different thermal parameters of pile how to effect the CFG pile temperature, and obtain some conclusions. |
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