Study On Frost-heaving And Thawing-settlement Control Indexes Of Subgrade In Seasonal Frozen Region

China is the third largest country in the world with frozen soil area.Seasonal frozen soil is widely distributed,and itsarea reaches more than half of China's total land area.Restricted by highway construction conditions,it is difficult to use all non-frost sensitive materials for highway subgrade filling,and with the continuous improvement of the concept of highway construction,low embankment with obvious land saving effect has been widely used in the construction of seasonal frozenregion.The frost heave and thawing of subgrade will cause the pavement cracking,the uneven deformation and the decrease of the overall bearing capacity.The deformation and subsidence caused by frost heave are difficult to be maintained,which have great influence on the safety of traffic,and the seasonal freezing and frost heave have become an important problem that plagued the construction and operation quality of the highway subgrade in seasonalfrozenregion of China.In recent years,the highway design technology and concept have been developing continuously.The low embankment road with the advantages of safety,less land occupation,environmental protection,and good coordination with the natural environment has become the trend of future development.However,because of the high underground water level of the low embankment and the increase of humidity,the hidden danger of frost heave and thaw settlement has been greatly increased.In addition,due to the influence of pavement construction and other factors,the interlayer of the pavement structure can not be completely bonded.The relationship between the frost heave and thawing deformation of the subgrade and the permissible cracking of the pavement structure will become more complex,and the control of the pavement cracking will be more unfavorable.Therefore,it is more necessary and meaningful to study the control index of frost heave and thaw settlement of roadbed based on the coordination and integration design of subgrade and pavement deformation.This paper takes frost heave and thaw settlement of the subgrade in quarried area as the research object.Through the observation and monitoring of frost heave and thawing deformation of highway subgrade in Jilin Province,the monitoring methods of frost heave and thaw settlement and the control index of subgrade frost heave and thaw settlement based on pavement cracking and evenness control are systematically studied.Through the deformation observation and monitoring of frost heave and thaw settlement of typical roadbed,the variation of frost heave and thaw settlement of subgrade over time is analyzed.Distributed optical fiber sensing technology is used to monitor the subgrade frost heaving and thawing Shen deformation,proposed subgrade frost heaving and thawing deformation comprehensive monitoring technology.The influence of frost heave and thaw settlement on pavement cracking under 10 kinds of working conditions was analyzed.The fractured layer position of subgrade under frost heave and thaw settlement under different conditions was analyzed.Through the laboratory experiments,the influence of frost heave and thaw settlement boundary conditions and different factors on the frost heave and thaw settlement of subgrade soil was proposed.Based on the theory of pavement structure response,the control index of subgrade frost heave and thaw settlement in seasonal frost area was proposed based on the analysis of subgrade frost heave and thaw settlement under the control of pavement cracking and evenness.The results show that the allowable frost heave value of the subgrade of semi rigid base asphalt pavement is not more than 25 mm,and the allowable frost heave value of the subgrade of the flexible base asphalt pavement is not more than 50 mm.