Experimental Study On Salt Expansion And Frost Heave Characteristics Of Sulfate-containing Coarse-grained Fillings From Lanzhou-Xinjiang High-speed Railway Subgrade

In recent years,the railway construction in the northwest cold and arid regions has developed rapidly,and the proportion of high-grade railways has become higher and higher,which puts higher requirements on the stability of saline soil subgrade.High-speed railways face a series of salt frost heaving problems when they pass through the saline soil belts,which may eventually lead to speed limit and cause great difficulties for high-speed rail operations.In this paper,the roadbed filler at K2456+296 in Yumen section of Lanxin High-speed Railway is taken as the research object.Through the field investigation,theoretical analysis and laboratory test,the salt heave expansion characteristics of coarse-grained sulfate soil are studied,and the main research results are obtained as follows:(1)Through the field investigation of the diseased section and the laboratory test of the basic properties of the subgrade fillings,it is considered that the local hydrogeology,climatic conditions and the use of local saline coarse-grained soil as the subgrade fillings are the main causes of the salt frost heave disease of the subgrade.(2)According to the dissolution characteristics of sodium sulfate in pure water,the crystallization law of sodium sulfate is analyzed in detail.Through calculation,it is found that the critical crystallization temperature of sodium sulfate increases with the increase of salt content and decreases with the increase of water content,while the crystallization of sodium sulfate needs to be analyzed according to its initial state of existence.(3)The salt-frost heave test of natural graded coarse-grained sulphate saline soil under different salt content,water content and compactness conditions shows that the critical crystallization temperature of the sample increases with the increase of salt content,decreases with the increase of water content,and has no obvious relationship with compactness.The freezing temperature increases with the increase of salinity from 0.7%to 1%and then decreases.It increases with the increase of water content and has a large dispersion with the change of compactness.With the increase of salt content,the total salt-frost heave deformation reaches a peak value at 0.5%?0.7%salt content,and then first decreases,then increases.The relationship with water content also needs to be divided according to the range of salt content.With the increase of compactness,there may be a double peak value change,which first decreases,then increases,and finally decreases.(4)The salt-frost heave test was carried out by changing the particle size distribution of the sample.The results show that the change trend of the salt frost heave test results of the samples with different particle size distribution is approximately the same.The increase of the fine particle content increases the salt-heave deformation of the.sample to a certain extent,and changes the salt content corresponding to the peak deformation at the negative temperature stage.(5)The results of salt frost heave test with sodium chloride show that the addition of sodium chloride improves the critical crystallization temperature of the sample and reduces the freezing temperature of the sample.Cl-has a significant effect on the freezing temperature of the soil.Sodium chloride has a good inhibition effect on the frost heave of the soil,and the effect of salt heave needs to be judged according to the initial state of the soil and the range of temperature change.