Frost Heave Monitoring On Subgrade Of High-Speed Railway By Precise Trigonometric Leveling

There is widely distributed with seasonal frozen soil in the south of China. With the rapid development of high-speed railway construction, A number of high-speed railways had been built in seasonal frozen soil area of China. The subgrade of high-speed railway is facing the frost heave problems in these areas in winter and spring seasons. Although a variety of measures were used to prevent frost heave on subgrade, it is still inevitable. It is very significant for the safely moving of the train using appropriate methods to monitor the deformation of frost heave. Precise trigonometric leveling had been used in many situations to replace the first and second class level measurement. But it is still unknown whether it could be used to monitor the variation of subgrade in such harsh condition where the temperature is very low. Therefore a method of frost heave monitoring was proposed in this paper based on trigonometric leveling using measuring robot. This can be used to study the feasibility and explore the rules of frost heave on subgrade.According to above research objectives, the principle of trigonometric leveling and errors to affect precision of triangle elevation difference were elaborated in this paper. Then the method of free station trigonometric leveling was used in the observation to reduce error sources and increase accuracy of measurement while considering the efficiency of measuring. In order to study the correlation between frost heave on subgrade and track irregularity, total station and track surveying trolley were used to measure the elevation of rail surface. Then the variation of height on subgrade was compared to that of rail surface in same mileage to analysis the influence of frost heave on subgrade to track irregularity.A suitable monitoring model must be established to gain the deformation of frost heave and study the variations by using trigonometric leveling. The precise leveling of high-speed railway was used to check the stability of point CPIII in this paper. The height of trigonometric leveling was compared with that of the second class leveling to make sure whether the precision could meet the need. As to free station-type trigonometric leveling, suitable observation models must be established when measuring. The adjacent direct elevation differences could be converted into indirect elevation differences. The weight matrix was determined according to the cofactor matrix considering the correlation of indirect elevation differences and then adjustment could be carried out. A software of data processing was developed based on trigonometric leveling according to these factors. The software can be used to adjust and analyze data of frost heave.The analysis of data shows that the frost heave monitoring based on precise trigonometric leveling is feasible in cold area of China. It can meet the precision of the second leveling survey when the temperature is no lower than-15℃ and the precise leveling survey of high-speed railway when the temperature is no lower than -25℃ by using the total station TS30 whose angle measurement precision is 0.5".The height of monitoring points were back to the state of initial value after a freezing and thawing cycle when the affection of ground settlement was eliminated. The development rules of frost heave is similar to the previous. The deformation of the subgrade shows following behaviors when it is compared to the height on rail surface. These research results above are reference and valuable for the application of trigonometric leveling and exploration of frost heaving deformation.