The Research On Nanjing Subway Typical Soil Frozen Thermal Physical And Mechanical Property

With the rapid economic development, urbanization has improved continuously, urbantraffic pressure continued to increase. The best choice to solve the urban traffic pressure isconstructing underground transport system, subway came into being. In the soft ground and thehigh degree of urbanization of Nanjing, it requires the artificial freezing method.Grasp the permafrost thermal physical and mechanical properties is the necessary conditionsin the design process of the Artificial Freezing Method premise of rational design and safety ofconstruction. In this paper, by Nanjing Subway typical soil frozen temperature, thermalconductivity, frozen heaving rate and thaw-settelment coeffient, undisturbed soil uniaxialcompression test, remodeling frozen silty clay triaxial shear test had studied deeply. The mainconclusions are as follows:(1) The Nanjing typical soil (silt mass silty clay, silty clay, silty) of undisturbed soil andremolded soil frozen temperature, the thermal conductivity was analyzed. The freezingtemperature and the thermal conductivity increased with the increase of moisture contentincreases, also showed a trend of increase with the increase of dry density, but the trend is notobvious. Coefficient of thermal conductivity under-10℃is about1.5times than normaltemperature conditions. Using BP neural network to the influence factors of frozen temperatureand thermal conductivity prediction model, got the normalized data table.(2) The Nanjing typical soil undisturbed and remolded soil frozen heaving and thawsettelment coeffient was researched. The rate of frozen heaving and thaw settlement coefficientincreased with increasing moisture content. And dry density increase to the rate of frozen heavingand thaw settlement coefficient is not significant, with a inflection point. Cold junctiontemperature to reduce frost heave rate increases. With the external load increase rate of frostheave and thaw settlement coefficient approximation was reduced power function trend, andthaw settlement process back the bomb volume has continued to grow and the longer timerequired.(3)Based on the analysis of Nanjing typical soil undisturbed soil uniaxial compression test,draw artificial ice compressive strength, elastic modulus increases linearly with decreasingtemperature.(4) By remodeling frozen silty clay triaxial shear test analysis, we can see the breakingstrength increases as the temperature decreases, the confining pressure increase in breakingstrength increases linearly; through the stress-strain curve of analysis and Duncan-Changmodel-based theory of frozen silty clay constitutive model, the model parameters was derived.