Study On Impact Of Freez-thaw To Piles Of Foundation Pit In Seasonal Frozen Zone

In recent years,the scale of foundation pit engineering is more and more bigger,the time limit for a project is getting longer and longer,many foundation pits are involved in the problem of wintering.especially in the seasonal frozen zone,foundation pit is impacted not only involved the frost heave of soil,also included the spring melting process of soil,which makes foundation pit engineering experience the complex freeze-thaw cycle.Related technical problems to be waiting solved,the research content has important research significance and engineering practical value.Therefore,this article selects pile support be used widely to carry out the research work of freeze-thaw action on pile foundation pit supporting in seasonal frozen zone,the main results as follows:First,research history and present situation at home and abroad on the impact of freeze-thaw action on pile foundation pit engineering are summarized in detail.Second,combined with the theory of the existing research results,this paper analyzes the stress deformation characteristics,failure mode and its influencing factors of the freeze-thaw action of pile foundation pit.Third,the basic theory,methods and steps of the application of flac3 d to simulate analysis freeze-thaw action on foundation pit are introduced in detail.Fourth,the numerical simulation results show that: with the time increasing of frost heave and the temperature lower,frozen deep gradually increase;displacement of the pile top grows;horizontal force behind pile increase in the overall;bolt axial force value increased gradually.When the rise of temperature and permafrost melts,frost temperature line is up,finally the whole model is warm;displacement of pile top still increases,but growth rate obviously less than the growth rate of the freezing phase displacement of pile top;horizontal force behind pile increase is less than soil pressure value of without frost heaving;the value of bolt axial force decreases.By comparing with the field monitoring results,partly the reliability of the numerical simulation method be verified.Fifth,the research results about influence factors show that: the frost heave and melting phase,the lower the temperature,the bigger the pile position displacement;the more fine soil particles,the frost heave effect is more sensitive,the bigger the pile position displacement;the higher the water content,the bigger the pile position displacement.By capping pile to overcome horizontal force behind pile be influenced by pile position displacement,it is concluded that temperature is lower,the bigger the horizontal force of pile,the larger the frost heaving force in the stages of frost heave and melting;soil frost heave phase particles is more fine,more easy to frost heave,the frost heaving force is more greater,when soil melt the frost heaving force is maximum in clay,the frost heaving force is minimum in silt;moisture content is higher,the more prone to frost heave,the frost heaving force is more greater in soil frost heave phase,the higher the water content,frost heave force is smaller,the lower the water content,soil frost heave force is larger in melt phase.