| Frozen soil refers to all kinds of soil that contains ice and is in a cemented state with soil particles and rocks at temperatures below 0?,that is,composed of solid mineral particles,water,ice,and gas.Frozen soil is a special soil with a multi-phase system.Its properties are affected by ice content,and the amount of ice content in the soil is closely related to its temperature.Therefore,frozen soil is sensitive to temperature changes and unstable in nature Special soil.my country is one of the countries with the widest distribution of frozen soil in the world.The area of seasonal frozen soil and permafrost accounts for about 2/3 of the total land area of the country.When the temperature drops below the freezing temperature,the soil body freezes,and the soil body appears frost heave phenomenon,accompanied by frost heave force.Alternate temperature changes in buildings and structures in cold areas will inevitably cause frost heave and thawing problems,resulting in damage to buildings and structures.Soil frost heave is an important challenge to be faced in the construction of cold area projects,and also one of the important factors of infrastructure damage.Various freezing damage problems will cause great losses every year.Therefore,it is of great practical significance to conduct in-depth research on the characteristics of loess' s frost heave,horizontal frost heave and temperature field.Aiming at the frost heave development law and freezing damage problem of loess,this paper uses the self-designed one-dimensional freezing and thawing model test system,taking the Lanzhou loess roadbed as the research object,and analyzing the one-dimensional freezing conditions through the combination of indoor model test and numerical calculation.The frost heaving characteristics of loess in the lower Lanzhou area established a water-heat coupling calculation model of the soil temperature field,numerically calculated the soil temperature field,and compared the numerical calculation results with the model test results to verify the water The correctness of the thermal coupling calculation model.The research results can provide a reference for the anti-freezing design and freezing damage management of the frozen ground area project.The main research contents and conclusions are as follows:(1)Design a one-dimensional freeze-thaw model test system,mainly including:freeze-thaw cycle environment box,boundary conditions and temperature control system,temperature measurement system,frost heave force measurement system,frost heave volume measurement system five parts.A one-dimensional freeze-thaw model test was designed and carried out to obtain the distribution and change law data of temperature field,frost heave volume and horizontal frost heave force in soil under different conditions.(2)The change law of soil temperature field was studied through model test.The cooling process of the soil at different depths can be divided into three stages: the first stage is that the temperature of the soil at each depth falls faster at the initial stage of cooling andfreezing;then The soil cooling rate curve of the depth of the soil layer near-0.4? is almost parallel to the stable section of the abscissa;the temperature of the soil at the end of the third stage continues to decrease at-0.4?,the rate of decline is slower than that of the first stage,and the higher the water content This phenomenon is more obvious;the temperature decrease rate of soils at various depths in the later period of freezing is slower.The change law of soil temperature is similar under different conditions.The higher the soil moisture content,the faster the soil cooling rate,and the lower the freezing temperature,the faster the soil cooling rate.The plateau of soil temperature has a large difference with the depth.The shallower the depth,the shorter the duration of the constant phase in the freezing process,and the duration of the plateau is smaller with the change of water content.(3)The development law of soil frost heave volume under different conditions is studied.The change curve of soil frost heave deformation volume is divided into three stages according to the change trend: micro frost shrinkage stage,frost heave rapid development stage and frost heave pseudo-stable stage The difference in the time for soils with different water contents to go through each stage is small,and the time for soils to go through stages in different freezing environments is different.The amount of frost heave deformation of soil increases with the increase of its water content.During the cooling process,the amount of soil frost heave is linearly related to the environmental freezing temperature.The lower the temperature,the smaller the amount of frost heave.(4)The initial temperature of frost heave force development is the same under different conditions of freezing temperature and soil moisture content,which is about-0.6?.Under different environment freezing temperature and soil moisture content,the maximum frost heaving force temperature is large.difference.The change trend of the horizontal frost heave force of the soil is different under different conditions.The maximum value of horizontal frost heave force varies significantly with water content.The higher the water content,the greater the horizontal frost heave force,while the other values are less affected by the water content.The maximum horizontal frost heave force is first along the soil depth.The change is relatively small,then increases to the maximum value,and finally decreases.The maximum horizontal frost heave force appears at a relative depth of 0.6-0.8.(5)Establish a numerical calculation model of water-heat coupling and numerically calculate the change law of soil temperature field under one-dimensional freezing conditions,and obtain the change law under different water content and ambient temperature under freezing.Comparing and analyzing the measured value and numerical simulation value of the model test at various points at different depths,it is found that the temperature change curve of each point of the numerical simulation is basically consistent with the measured temperature curve.The cooling rate of the numerical simulation during the freezing stage is slightly greater than the measured cooling rate,melting The phase is reversed.The results of the study can provide a reference for the construction of frozen ground areas. |
PDF Full Text Request