Study On The Influence Of Whether Water Supplementation And Load On Frost Heaving Characteristic Of Silty Clay

The problem of frost heaving and thawing settlement has always been a problem in the research and application of artificial freezing method.The application of external load to suppress frost heave has been partly applied in practical engineering,but indoor research still stays in the small load stage,and the impact of large load on the frost heaving characteristics of frozen soil is less.This requires further research.In this thesis,Shanghai silty clay is taken as the research object,and the external load and hydration conditions are selected as the influencing factors.Firstly,the loading and water replenishment system of the existing frost heaving and thawing sedimentation test device is improved so that it can meet the test requirements and more scientific and reasonable.Secondly,the method of making remolded soil samples is studied emphatically so that the physical state of the sample under natural overburden can be simulated.The last,the characteristics of frost heave,the development law of freezing front,the law of water replenishment and the law of water distribution is systematically studied to analysis of test results comprehensively.In this way,the effects of external loading and water replenishment on the characteristics of soil sample during freezing and after frost heaving and the distribution of water transfer and redistribution can be studied.This thesis’ studies provide a basis for freezing engineering of artificial freezing and temporary stowage restraining frost heave of urban subway.The following are the main achievements:(1)The improved frost heaving and thawing sink test apparatus is reasonable and feasible which loading system can meet the loading requirements of large loads,and water replenishment device can reduce the influence of water weight and accurately read the water replenishment amount in real time.The samples produced by the new method have good uniformity and structure so that they can fully meet the test requirements.(2)Under the same load,the temperature drop of the closed system sample and the development rate of the front surface are faster,and the stability is earlier.However,when the high load is applied,the difference between the temperature and the front development of the two kinds of hydration is gradually reduced.Under the same hydration,with the increase of load,the temperature drop and the development speed of the freezing front are faster in the early stage of freezing,the slower in the middle and late stage,and the earlier the steady state is reached.(3)Under the same load,the frost heave of the closed system in the early freezing period develops faster in the early freezing period,and the frost heave of the open system in the middle and late freezing period develops faster in the early freezing period,but the difference between the frost heave of the open system and the closed system becomes smaller and smaller under the high load.Under the same hydration conditions,as the load increases,the time for the initial freezing of the sample is more and more delayed,the rate of frost heave development is lower,the final frost heaving is smaller,the development of frost heave of the closed system reaches the stability is earlier and earlier,and the open system has gradually developed a trend of stable development.The frost heave rate of the two hydration systems decreases exponentially with the increase of external load,and the open system is more affected by the load.The difference of frost heave rate of the two hydration systems is smaller and smaller,which is reduced from 3.3times of the load to 1.2 times with the increase of the load.(4)Under different hydration modes,the variation of the height of frozen soil samples is opposite.With the increase of load,the height of the frozen soil samples in the closed system is decreasing,while the open system is increasing,and the difference between the two systems is smaller and smaller.(5)The change of water replenishment in the unloaded system is divided into four processes:no replenishment phase,exponential increase phase,logarithmic increase phase and linear increase phase.After the load,the no-water replenishment stage becomes a negative replenishment stage.With the load increasing,the amount of water replenishment in each stage is smaller and smaller,the duration of negative water replenishment is longer,the negative growth is greater,and the time that water starts to replenish is later.After the freezing is completed,the final water replenishment decreases exponentially with the increase of the overlying load.(6)After the frost heave,the water distribution of the sample decreases in the upper part and increases in the middle and lower parts.When there is no load,the increase of the water content at the maximum position in the open system is more than 10 times that in the closed state.Under the same hydration condition,with the increase of load,the moisture distribution of the closed system sample changes from the "hook" distribution when there is no load to the "angular" distribution when there is load,while the open system is "angular" distribution.The larger the load,the smaller the change in moisture content at each height.The load can significantly inhibit the migration of outside moisture,the larger the load is,the less obvious the effect of water rehydration is.This results that water distribution patterns of different hydration methods are more and more similar,and the difference in water content at each height is getting smaller and smaller.Under the open condition,the maximum moisture content decreases linearly with the increase of load,but under the closed system,the maximum moisture content remains around26.3% with the increase of load.