Analysis Of The Influence Of Frost Heave On The Stability Of Foundation Pit In Seasonal Frozen Zone

With the continuous development of society and the increasing speed of population urbanization,various underground projects and high-rise buildings are being constructed,which brings the necessity of foundation pit design and construction on special soil.The frost heave safety of foundation pit construction in seasonal frost heaving area has attracted more and more attention in China.The special physical and mechanical properties of soil in this area are the key factors affecting the stability of foundation pit.How to ensure safety in the design and construction of foundation pit in seasonal frozen area,how to consider the influence of frost heave of soil on supporting structure and how to design frost heave of soil in the construction of foundation pit over winter The calculation method and the anti-freezing measures should be adopted for the sudden drop of temperature are the focus and direction of scholars’ research.Seasonal frozen soil refers to the special frozen soil on the surface of the earth’s crust which freezes in winter and melts in spring.Compared with short-term frozen soil and permafrost,the repeated frost heave and thaw effect of seasonal frozen soil brings different stress fields in the foundation pit,which makes it difficult to calculate the redistribution law of earth pressure and stability of foundation pit after excavation.At present,there are no specific norms and measures to prevent frost damage for frozen ground in seasonal frozen area.Therefore,it is necessary to have a deeper understanding of the freezing mechanism,strength of the frozen soil in the seasonal frozen zone and the impact of the supporting structure.On the basis of previous studies on frozen soil,this paper introduces the Frost Heave Mechanism of frozen soil and its influence on retaining structure,and analyses the water transfer mechanism of frozen soil in the process of freezing.Combining with the existing theoretical research results,the strength of frozen soil is elaborated in detail.Taking an overwintering foundation pit project in Shenyang as an analysis case,the excavation foundation pit is simulated and analyzed as the research object.Flac 3D software is used to calculate the horizontal displacement of the enclosure structure of the model,and compared with the actual monitoring data to verify the accuracy of the parameters and the feasibility of the model.In view of the different factors affecting the frozen soil,the thermo-mechanical coupling model of foundation pit is established by taking the common foundation pit supporting structure in seasonal frozen area as an example,and the effects of soil properties change and the stress and deformation of the supporting structure during the freeze-thaw cycle are analyzed.According to the above research,with the decrease of temperature,the soil begins to frost heaving and produces larger frost heaving force in seasonal frozen area,but the growth speed of pile displacement is not fast,the frost depth is shallow,the growth rate of pile top displacement increases in the middle and later stages of frost heaving,and the frost heaving force increases to the maximum.The frost heaving effect of frozen soil causes the horizontal force of pile body to reach 400% of unfrozen soil.The effect of thawing is very obvious.Ice formation causes a large amount of water to migrate to the frozen margin zone,and the frozen margin zone contains a large amount of gel icing.After thawing,a large amount of water is discharged,and the soil structure of the frozen margin zone begins to destroy,showing special rheological properties,accelerating deformation until complete destruction.The internal properties of different soils are different in the frost heave stage,and silty clay is sensitive to frost heave.Maximum.In the stage of melting soil,the horizontal force values of pile body have little difference,and the difference of particle size composition has no effect on the melting soil.The ice melting formed after water migration will destroy the original stable structure of the soil.