Experimental Research On Engineering Properties Of Cement Stabilized Macadam Subgrade In Cold Regions

The high-speed railway subgrade frost damages are becoming more and more serious in the cold and frozen regions,which seriously affected the railway traffic safety.This has become a difficult problem to be solved in the design,construction and operation of high-speed railway in cold area.Based on the key project of science and technology research and development program of China railway corporation "the service performance evolution of subgrade under freezing and thawing and high speed train load in severe cold area"(2014G003-F).Taking the high-speed railway subgrade in cold area as the research background,the cement stabilized macadam subgrade was selected as research object,in-depth analysis the effects of cement content and particle size gradation on the frost heaving performance,strength property,durability and shrinkage deformation of cement stabilized macadam.Founding the reasonable structure of the cement stabilized macadam subgrade bed.The main research contents and achievements are as follows:(1)Through the test of frost heaving deformation,the results show that the soil particle size and cement content are the key factors affecting the frost heave rate when the water content is constant.The frost heave rate increases with the cement content,decreases with the increase of the particle size of the removed particles.(2)The larger the particle size of the cement stabilized macadam was removed,it has the better permeability;but also because of the lack of particle size,its strength decreases.Considering the frost heave rate,permeability coefficient and unconfined compressive strength of cement stabilized macadam samples,Fine graded content of not more than 3%?at the same time mixed with the 3% cement and removing the particle size below 0.5mm?mixed with 3% to 5% cement these graded gravel were selected to meet the requirements.(3)By the durability test of the selected cement stabilized macadam,the results show that the existence of fine-grained soil can keep the water stability of the samples well.When the cement content is between 3% and 5%,the water stability of the cement stabilized macadam which removing the particle size below 0.5mm is also better.In addition,with the influence of the number of freeze-thaw cycles,the strength of the samples decreased at different degrees,which mixed with 3% cement to remove particles below 0.5mm particle size and fine grain not more than 3% at the same time into 3% cement,these frost resistance are relatively better.(4)Based on the experience of the highway,the shrinkage and deformation properties of different cement stabilized macadam samples were studied,founded that the most unfavorable temperature range of the cement stabilized macadam base in the dry state was 10? ~-10?,because the temperature coefficient at the moment is the largest.The shrinkage coefficient increases rapidly with the exposure time of the sample and became stable after 11 d;when the same particle size distribution,the more cement content,the greater the coefficient of shrinkage.(5)Through the study of durability and shrinkage deformation test,verified the feasibility of the different cement stabilized macadam samples,it is considered that the graded gravel with fine grained content of not more than 3% at the same time mixed with 3% cement meets the requirements of the non-permeable bed in the cold area;For the permeable bed,it is more reasonable to choose graded gravel with removing the particle size below 0.5mm and 3% cement.