Investigation On Properties Of Frost Heave And Thawing Settlement Of Cement-improved Soil

Artificial Ground Freezing method(AGFM)is more and more widely used in underground constructions in the area of soft soil.However,frost heave and thawing settlement exert bad influence on the constructions and surroundings,what's more, result in accidents.Therefore,methods of controlling frost heave and thawing settlement need to be studied immediately nowadays.It is the essential way to reduce thawing settlement by controlling frost heave.Accordingly,at the background of the Shanghai Yangzi River Tunnel and the Renovation Project of Line 4 of Shanghai metro,the technology that the soil should be improved by cements before artificially freezing is studied in the dissertation in order to reduce frost heave to fatherly control thawing settlement.Lacking of theory and experience adapting for projects in China,experiments should be considered to validate the technology.⑤₃ silty clay and⑦_-2 silty sand, respectively denoting soft soil and sand in Shanghai that is one of the most typical soft soil regions in China,are studied by experiments after they are improved by cements so that the technology is well researched.The research involves several aspects as following:(1)To find out the basic difference between⑤₃ and⑦_-2 by the basic soil test, and investigate density,water content,penetrability.It is detected that penetrability of cement-improved soils falls.(2)By the method of mechanics test,the different freezing properties of the two soils are compared,meanwhile,the alteration of mechanics parameters of the cement-improved soils are investigated.It is indicated that the freezing properties of the two soils are enhanced after they are improved by cements.Unconfined compressive strength is augmented in the relation of exponent with cement when the temperature falls.(3)To research on how the content of cements influent the rate of frost heave and thawing settlement by the frost heave test and thawing settlement test under open-system freezing.It is found that the frost heave and thawing settlement of soils mingled with cements is reduced distinctly.The reason of controlling frost heave is that moisture transfer is confined due to cements.The prime theory is that penetrability of cement-improved soils falls resulting in limiting moisture transfer, which can prevent absorbing necessary water when frost heave happens.Hereby,frost heave can be restricted.On the other hand,the combination among soil grains is reinforced owing to the join of cement grains,which can hold back settlements when the frozen soils are thawing.(4)The swelling of ground in virtue of frost heave of underground frozen soils is regarded in projects at all times.However,the technology studied in the paper has been applied and validated.In the paper,the validity of the technology is testified theoretically by the method of combining the experimental data and the model that simulate the swelling of ground in virtue of frost heave.The maximal swelling of ground and whole swelling of ground can be reduced when cement-improved soils are freezing,which accounts for the technology can weaken infection that frost heave exert on surroundings.In conclusion,the technology not only strengthens the freezing properties but also controls frost heave and thawing settlement effectively.Thus,the technology is worth applying in artificial ground freezing projects.