Frost Heaving Deformation Of Heavy Haul Railway Subgrade Filling In Seasonally Frozen Region

In the process of building heavy haul railway in China,fine-grained soil has been widely used as subgrade bed material.However,in the seasonal frozen region,the large deformation of fine-grained filling is easy to be caused by freeze-thaw cycle in subgrade,which greatly affects the transportation efficiency and safety of goods.Therefore,it is of great guiding significance for the maintenance of existing lines and the construction of new lines to study the frost heave deformation characteristics of heavy haul railway subgrade filling.Based on the research background of subgrade disease of Shenchi-Ningwu section of Shuozhou-Huanghuagang Port Railway,this thesis studies the frost heave deformation of subgrade filling by means of field monitoring and laboratory test.Through filed monitoring,the laws of ground temperature,water content,frost heave deformation and vibration acceleration of railway subgrade in seasonal frozen region are explored,which provides a reference for the design of laboratory tests.The frost heave characteristics of fine-grained soil were studied by laboratory tests,and the local deformation and cold structure of soil were analyzed by Particle Image Velocimetry(PIV)technology.The main work and conclusions are as follows:(1)Based on the remote monitoring system constructed at thetypical section of subgrade diseases,the variation rules of ground temperature,water content,frost heave deformation and vibration acceleration are analyzed.The results show that:it is found that under the influence of atmospheric temperature,the temperature and water content of subgrade change accordingly,which leads to frost heave and thaw settlement deformation.There are differences in ground temperature and deformation in the transverse direction of the monitoring section;the water content is mainly affected by atmospheric precipitation.During the freezing period,the stiffness and uneven deformation of the subgrade increase,which leads to the aggravation of the vibration response when the train passes.(2)Under the open system,the indoor frost heave test of the soil column under step cooling was carried out to explore the frost heave deformation laws of the subgrade filling.It is found that during the cooling process of each step,the temperature gradient in the freezing zone increases first and then decreases,and finally tends to be stable.The maximum temperature gradient is 2.48℃/cm.As the temperature of the upper cold bath plate decreases step by step,the ice lens body is formed step by step along the frost depth,resulting in an increase in frost heave.During the test,the soil column has been in the state of water replenishment,which can be roughly divided into slow,rapid and linear water replenishment stage.After freezing,the maximum water content appears near the freezing front of the soil column.(3)Combined with PIV technology and cryostructure,the local frost heave deformation law of subgrade filling was explored.It is found that during the freezing process of soil column,frost heave deformation occurs above the freezing front,and compression occurs below the freezing front.The temperature range of ice lens growth is lower than the freezing temperature of the sample;under the step cooling,with the decrease of the temperature of the upper cold bath plate,the overall structural strip in the frozen soil area decreases.With the increase of the freezing depth,the thickness of the thin-layer structural strip in the frozen soil area increases,while the ice lens structural strip and the overall structural strip in the unfrozen area decrease.