Thermodynamic Behavior Research On The Soil Structure About Urban Environment

With the urban expansion and the population condensation, the "heat island" phenomenon becomes prominent day by day, and this causes changes in temperature field in the urban underlying rock-soil mass. The additional urban geothermal field is bound to cause changes in moisture content of the soil, ion-chemical field and the physical-chemical properties of liquid and solid phase of the soil mass, and thereby changes the connection, the absorption and the behaviors of the soil particles, and influences the structural intensity of the soil mass. In this case, how will the structural intensity of the soil mass change and what heat sensitive component will be there? These two problems are worth being studied in geo-technical field. In our country, the researches on the influence of temperature on the rock-soil medium are carried out mostly for the mechanical-deformational behavior of the frozen soil under low temperature conditions in cold areas and its engineering influence. These researches generally based on the frozen soil below 0C mainly study its freeze-thaw cycle action and its moisture migration mechanism. The problems about the temperature effect of rock under high temperature conditions also are paid certain attention to. Its engineering backgrounds are mainly the disposal-storage of nuclear waste and radioactive materials, and its research object is usually the material of rock mass. But we can rarely find the researches on the thermodynamics of clayey soil with different salt components in pore liquid of soil mass at normal temperatures (below 60C) and pressures. So, basing on the urban environment, it has important theoretical and practical significance to choose these two problems as the research issues of dissertation.Aiming at aforementioned research problems, this dissertation analyses the disturbance level caused by the variation of the surface temperature to the underlying clayey soil, and the physical-chemical manifestation of clayey soil acted by heat at normal temperatures and pressures. At the same time, this dissertation approaches through experiments the discrepancy of the mechanical attribution of clayey soil under the action of temperature field, researches two external factors (temperature and time) that influenced the thermodynamic behavior of clayey soil, and presents the analytical results of temperature effect and time effect of the thin-view structure of clayey soil. With the increase oftemperature, the value of cohesion rises progressively and there is an abrupt segment between 30C and 50C, but the value of the angle of internal friction is fluctuated. After the time sequence has been lengthened, the value of cohesion still rises, while the value of the angle of internal friction fluctuates and the whole effect takes on a decreasing trend. Therefore, the experimental result that the variation of the temperature field causes the changes of the moisture and chemical fields confirms the fact that the urban heat island can affect the urban underlying clayey soil and cause the variation of the soil mass behavior.The liquid phase of soil is a very dynamic part in the structure of the soil mass. When the urban underlying clayey soil has heat disturbance, the motion of internal ions in soil mass begins to change. It can change the inter particle connection through the separation of pore solution's component in soil and the dissolution of particle mineral, thus influencing the structural intensity of the soil mass. From the mechanical expression of inherent attributions (including the moisture content of soil, the pore solution's component and the value of PH) of the thin-view structure of soil mass under the action of temperature field, this dissertation researches the influence of temperature and its acting time, the pore solution's component and the acidity-alkalinity on the thin-view structure of clayey soil. The experimental results show that the value of cohesion of the soil sample soaked in Na2S2O4 solution is the maximum when the temperature is 40C while the value of cohesion o...