Mechanism Analysis on Subgrade Frost Heaving in Seasonal Frozen Region

In order to master the frost heaving mechanism of subgrade and reduce the diseases of cracking,subsidence and mudding due to subgrade frost thaw in seasonal frozen region,the temperature sensors were embedded in the subgrade in heavy frozen region to automatically monitor the temperature of subgrade in freezing period.Drilling investigation of typical road frost disease was also conducted in seasonal frozen region.The results show that(1) Cooling range in the upper subgrade was great and cooling rate was high,and situ freezing occurred in the upper subgrade.(2) Cooling range in the lower subgrade was small and cooling rate was low,and sufficient moisture transfer and accumulation phenomenon occurred.This position is also the depth of ice gathering zone.(3) Ice form was different in different subgrade soils,and the depth and moisture content of different ice forms presented some regularity.(4) The mean depth of the ice gathering zone was 1.08-1.65 m,and the scope of mean moisture content was 14.7%-23%.The maximum moisture content approached or exceeded the plastic moisture content of soil.Therefore,the ice crystal separated,which formed the main component of frost heave.On the basis of the above research work,It is found that(1) Subgrade frost heave of seasonal frozen region is the course that different forms of ice structure compose the frost heave for heat balance continuously form and break with cooling impel and moisture transfer.It is suggested that drainage and water block measures should be proposed to control subgrade moisture and enhance the control for the homogeneity and density of subgrade filler so as to reduce and prevent the frost disease.