| Currently, the application of cast-in-place concrete pile rapidly rises in quantity and scale in domesticTT TTpermafrost region, and there are such a series of problems as calculation of bearing capacity forming time of single pile during construction, change law of bearing capacity with thawing settlement in summer and influence of creep settlement of frozen soil around pile on bearing capacity in service stage. All the problems have been generally concerned focal problem at home and abroad and the research on bearing capacity has been one of the front subjects in frozen soil engineering.Based on systematic summary and deep analysis of relevant research at home and abroad, the following research in three aspects was carried out on the principle of temperature of frozen soil through the investigation of freezing damage and comparison between test and numerical simulation.1.The relevant experimental devices were developed, four series of tests were conducted such as thermal conductivity test on frozen soil, freezing strength test, hydration heat test on cement with different ingredients of admixture and thaw-settlement negative friction test on pile with different water content frozen soil, so all the above research provided important parameters for FEM calculation. 2. Grounded on different heat transfer model, nonlinear model of frozen soil and test data of static triaxial experiment on frozen soil, the calculation program was designed to compute temperature field of frozen soil surrounding pile and settlement of pile under load. Through plenty of calculation work, the distribution rule of adfreezing force of pile was obtained, as well as the affecting law of every parameter on it. 3. According to the data of rheology experiment on frozen soil, a whole new nonlinear viscoelastic rheological model was founded. The bearing capacity of single pile in correlative engineering was modified through the developed program, which gave theoretical basis to control the freezing damage of projects in permafrost.The main research results as follows: 1. The calculation program of temperature field of frozen soil around pile was designed and provided. In terms of numerical calculation and comparison of temperature field of frozen soil around pile with different temperature of heat source (temperature of cast-in-place concrete) and different ingredients of concrete admixture, it was proved that the forming time of bearing capacity was shorten to 33 days, about 30 in advance, when the concrete admixture consisted of 10% fly ash, 5% silica fume, 3% early strength admixture and 0.8% water reducing agent.2. This paper proposed FEM calculation method and program of load-deformation of single pile in permafrost. It was founded that adfreezing force increased with the increment of pile diameter, which can effectively reduce amount of settlement by 30%."Neutral point of temperature"was founded through investigation into the change law of adfreezing force along pile length with variation of temperature of frozen soil. At the point, the forming of adfreezing force was free of the influence of temperature of frozen soil; above the neutral point side, adfreezing force increased with the reduction of temperature of frozen soil, but, below the neutral point side, it decreased with the reduction.3. According to experimental results of thaw-settlement negative friction, by Mindlin's solution, the theoretical calculation formula was proposed to compute the additional force owing to thawing collapse and its distribution law. In summer, bearing capacity of pile decreased by 8% or so in permafrost active layer thawing.4. FEM calculation method of settlement of single pile was proposed considering creep deformation of frozen soil. The calculation result of bearing capacity of single pile was compared with the experimental data of static load test in certain engineering, and it was concluded that ultimate bearing capacity of single pile reduced by about 10% under the influence of rheology of frozen soil.
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