Research On Characteristic Changes Of The Silty Soil Subgrade’s Engineering Environment Located In The High Water Level Seasonal Frost Region

In northeast china’s seasonal frozen regions,Rilway embankments are inevitably faced with the serious problem problem of frost damage both which has been built and under construction.It can provide the analysis basis for the study to master the various characteristics of the subgrade’s engineering environment,which is about causes of embankment’s frost damage in the deep seasonal regions.Based on the Railway Project built fromhuoshigang to bohai,two different height test sections of the silt soil subgrade are selected in this paper,which is located in Taian county of Liao ning Province. Through site monitoring, we carry out experimental study on moisture, temperature, water level and subgrade settlement deformation in thesilt soil subgrade’s engineering environment in seasonal frost regions, which is of the high water level.The conclusions are as follows:(1) The air temperaturehave a big influence on subgrade surface soil temperature;This influence is reduced withthe increase of roadbed depth; Besides, because of influences of transverse thermal difference, the temperature distribution imbalanceon both sides of roadbed leads to uneven railroads settlement deformation.(2) Because temperature, precipitation and water migration have great influence on the subgrade shallow surface soil, the moisture content distribution below the subgrade surface within the depth of 0~1.0 m is not uniform; Within the depth of1.5~2.5 m, water content is relatively stable; within the depth of 2.5~3.5 m,water content increased significantly,and the data is relatively discrete. Water migration accumulation phenomenon is significant in the maximum frozen depth of subgrade soil. Therefore, it is rather necessary to set waterproof insulation layer and drainage system of the subgrade surface near the maximum frozen depth.(3) The range of water level rising is closely related to the size of precipitation:Groundwater level rise relatively with the increase of the precipitation; The water level goes with the changes of seasons: from 9 to 12 months, the dry season comes and the water level occurred a decline of 0.183 ~0.186 m. From 12 to 3 months,the water level went on dropping and appeared a increase of 0.052~0.057 m.(4)The subgrade settlement deformation appear differences between the north-facing slope and the south-facing slope. settlement difference goes with embankment height increases. During the monitoring period, the maximum heaving quantity difference between the left shoulder and right shoulder in the high embankment(7.39 m)is 2.79 mm, that of low embankment(4.22 m) is 1.81 mm. The maximum heaving quantity difference of the high embankment is more than that of low embankment. Because of the effect of the north-facing slope and the south-facing slope,the subgrade settlement deformation difference goes with embankment height increases.It is the main factor which causes the uneven deformation of subgrade frost heaving.In addition, temperature and water are also important factors to cause the subgrade frost heaving.