Study On Frost Heave Properties Of Improved Coarse Grained Fillings For High-speed Railway

The subgrade deformation of high-speed railway has strict control standards. At present some sections of high-speed railway subgrade deformation in cold regions has influenced the operation of high-speed train. With the improvement of the waterproof and drainage measures for subgrade, the problem of subgrade frost heave has been partly eased. However the water still inevitably infiltrates into the subgrade fillings through the structural joints and cracks that has caused the subgrade frost heave. Consequently the focus of this paper is the improvement of frost heave properties of coarse grained fillings for high-speed railway subgrade.This paper summarizes the present frost heave status of high-speed railway and analyses the reasons and location of the subgrade frost heave on the basis of the collection and collation of information in the railway of cold regions. The inorganic materials are added in the graded gravel and A class fillings for improving the permeability and frost heave properties through the laboratory tests. The relationship between frost heave properties of various types of improved fillings and fine grained soil content, the mixed material types and content are analyzed. The technical parameters for the improved type and the most appropriate content of graded gravel and A class fillings are concluded with the standard of the certain frost heave ratio. This can reduce the amount of deformation of high-speed railway subgrade frost heave from the filling angle.The main conclusions are:(1) In the open supplying water conditions the frost heave ratio of the graded gravel increases with the silt content and it increases significantly when the silt content is more than 15%.(2) Compared with the lime and fly ash, cement has the most significant effect of reducing graded gravel’s coefficient of permeability with the suitable water stability.(3) In improving frost heave properties of graded gravel, the ratio of frost heave of graded gravel decreases along with the increase of cement content. The most appropriate cement content of the graded gravel with 15%,20%,25% silt is 3%,5%,5% with the standard of frost heave ratio 0.1%.(4) The improved graded gravel’s frost heave ratio increases after immersion in water, but still less than the graded gravel without the cement.(5) In the certain silt content the frost heave ratio of A class fillings is greater than the graded gravel because of the different particle sizes.(6) The combination of lime and fly ash is not suitable to improve A class fillings due to the rising height of capillary water and poor water stability. Cement greatly reduces A class fillings’ frost heave ratio compared with lime. The most appropriate cement content of A class fillings with 12% silt content is 9%. Considering the frost heave deformation of graded gravel layer the amount of deformation of improved subgrade frost heave is controlled within 3.55 mm, less than the standard requirements of subgrade deformation limit value 15 mm.The main innovation points are:(1) With adding the inorganic materials in the coarse grained fillings for high-speed railway the changes of coarse grained fillings’ permeability and frost heave properties are researched.(2) With the standard of certain frost heave ratio and the appropriate increasing silt content, the technical parameters for improved material type and appropriate content are concluded.