The Research On Filler Engineering Suitability Of Silt Sand Subgrade In Frozen Region

The railway project from Huoshigang to Bohai under construction is located in the middle of Liaoning Province,where is defined as seasonal frozen region.Due to the lack of high quality subgrade filler along the railway,the railway engineering was decided to use the local silt sand as subgrade filler.Because of poor grain gradation,low cohesion,and easying to be affected by freezing and thawing,etc.which lead to poor engineering properties of silt and many problems in the process of being applied to the subgrade engineering.Although the domestic and foreign scholars have carried out a lot of research on the silt sand,because of the difference of silt sand in different area in particle gradation composition,mineral composition and mineral content,etc.which have many differences in the engineering properties.The academic community still lacks systematic cognition to silt sand.For these questions,This paper is based on the second bid project of Huo-Bo Railway and combined with the local geological,hydrological,climatic conditions and actual situation.The study about the filler engineering suitability of silt sand subgrade in frozen region was carried out through indoor experiment and field test about the local typical silt sand.The results are as follows:(1)The engineering properties of silt sand were studied by laboratory tests of physics,mechanics,water-physical properties and SEM microscope scanning.The test results show that:The particle size of silt sand is relatively uniform and change mainly from 0.075 mm to 0.25 mm,the grain gradation of silt sand is poor;Good particle roundness and low clay content in the silt sand,which lead to low shear strength,difficult compaction and molding to be rolled,easy slip between particles.The shear strength can be improved by increasing lateral restraint;During the rolling process,water content of silt sand fillers can be controlled in a large extent,construction process is not affected by the rainy season;The roller times don't need too much,and the compaction degree of 90 % is easy to get.(2)The freezing-thawing properties of silty sand were studied by considering thefactors such as cooling temperature,compaction degree,water content and freezing-thawing cycles times.The study results show that: Silty sand belongs to weak frost heaving soil of grade II,it has higher resistance to frost heaving;In the closed system,the more water content,the lower temperature,the frost heaving amount and thawing settlement amount of silt sand is larger;Increasing degree of compaction can inhibit frost heaving force of silt sand to a certain extent and reduce frost heaving deformation;The long-term effect of freezing-thawing cycles can lead silt sand struction to be more porous,in the case of no water supply,the silt sand deformation of frost heaving and thawing settlement enter a state of dynamic stability after 7 times freezing-thawing cycles.(3)Based on the results of indoor experiment and field test and combined with actual situation of the field,the paper evaluated the suitability of silt sand filler comprehensively from various angles,and determined that silt sand is suitable for the railway subgrade filling.This paper not only Analysed and summarized the compaction mechanism of silt sand filler but also identified the thought and main technical parameters of compaction with "vibration and constraint equipment",and put forward the compaction technology with "vibration and constraint equipment" for silt sand subgrade.