Research On The Microscopic Features And Mechanical Properties Of Silty Sands Used In Subgrade In Seasonally Frozen Region

The area of seasonally frozen region are accounts for more than half of our land and are widely distributed.The road in this area under repeated freezing and thawing often occur drum kits,frost boiling etc.The physical and mechanical properties of subgrade will have undesirably change after freeze-thaw cycles,thus affecting the bearing capacity of foundation.So this paper studied the shear strength of silt and stability of embankment slope under freeze-thaw cycles,and analyzed the changes in the microstructure of silty sands under the effect of freeze-thaw cycles.At last,explored the relationship between microstructure and features of macro mechanics.The soil samples are obtained along the road in Changchun,according to the test results of compaction,specimen with more than 96% degree compaction are made in the best moisture content and this moisture content ± 2%.In the closed environment,we applied 0 to 16 freeze-thaw cycles to specimens.Then triaxial test was applied to these specimens.The variation law of shear strength,angle of friction and cohesion with the freeze-thaw cycles were acquired at different moisture contents.The results showed that: the shear strength of silt under the action of freeze-thaw cycles appear first decline and then stabilized variation,but due to the presence of moisture,the extent of decline in shear strength will be different;cohesion with the increasing number of freeze-thaw cycles had a decreased trend;friction angle had no rules to follow,but fluctuate within a certain range;cohesion and friction angle of soil at less water content is greater than the larger moisture.Since the clay of silty sands is less,cohesive is small,and the stability of water is poor.Therefore,even at low filling height,slow slope,the stability of the roadbed is also poor,especially the cohesion will be reduced after freeze-thaw cycles,and the greater possibility of subgrade instability under vehicle load.This article focuses on the embankment slope stability under natural state and freeze-thaw conditions.The results showed that: the soil,height,rate of slope,vehicle load is related to stability of Subgrade slope,and shear strength of soil is affected by moisture during the spring thaw.when water gathered at the interface to a certain extent,the soil will slide along the interface.The image of microstructure is obtained by Scanning Electron Microscopy.The basic geometric information of micro-structure is acquired by digital image processing technology and fractal dimension theories.By quantitative analysis of the variation of microstructure parameters after freeze-thaw cycles,Finally,the gray relational method is used to evaluate the relevance between shearing strength of soil and stability of embankment slope and these microstructure parameters under the action of repeated freeze-thaw cycles.