Experimental Study On Water Vapor Migration Characteristics Of Oil Shale Residue Improved Subgrade In Seasonal Frozen Region

Road disease problems are common in the seasonal frozen region,which seriously shortens the service life of the road and increases the maintenance cost of the road to a certain extent.The road mainly consists of subgrade and road surface,the subgrade provides support for the road structure and jointly with the road surface to bear the role of traffic load.The main manifestation of road disease in the seasonal frozen region are frost swelling and slurry.The roadbed soil is a typical unsaturated soil in which changes in water content lead to changes in soil properties.The migration of gaseous and liquid water under the effect of temperature difference between the top and bottom of the subgrade causes the change of water content which affects the stability of the subgrade.In winter,the water migrates from the bottom to the top to freeze into ice and then the volume becomes larger to squeeze the surrounding soil to form the phenomenon of freezing and swelling.When the temperature rises in the spring,the frozen soil melts and forms a water-filled layer,and the subgrade filler in the water-filled layer is repeatedly squeezed under the action of vehicle load,leading to the overturning of the subgrade.The vigorous development of oil shale has generated a lot of waste residues,and the production of waste residues has caused serious pollution to the environment.In order to mitigate environmental pollution and realize solid waste reuse,the group proposed oil shale residue improved soil with good physical properties,but lacked research on its anti-frost swelling properties.Water vapor migration in the subgrade is an important factor that leads to frost swelling and slurry of subgrade in the seasonal frozen region.Water vapor migration is divided into gaseous water migration and liquid water migration.Due to the difficulty of gaseous water measurement,there is a lack of research on gaseous water migration,but its effect on road frost swelling and slurry is not negligible.This paper is based on the National Natural Science Foundation of China project "Research on the mechanism of setting cold group layer to manage frost damage of roadbed in the seasonal frozen region（51578263）".The migration law of gaseous water in unsaturated soil is studied by the invented measurement device of gaseous water migration in unsaturated soil.The ratio between gaseous water and liquid water in subgrade soils was clarified by analyzing water vapor migration data.In order to alleviate the disease of frost swelling and slurry in the seasonal frozen region,the antifrost swelling property of oil shale residue improved soil was evaluated and a prediction model of gaseous water migration of oil shale residue improved soil was constructed.Based on the above research objectives,the main research contents of this paper are as follows:（1）An innovative test device for measuring gaseous water migration in unsaturated soils was invented based on the principle of mass conservation to measure the gaseous water migration mass of unsaturated soils with different water contents and compaction at different temperatures.The invented device is compared with existing gaseous water migration measurement devices by gaseous water migration tests to verify the accuracy and practicality of the invented device.（2）The invented device was used to study the migration of gaseous water between oil shale improved soil and silty soil at different temperatures and to analyze the effect of factors influencing gaseous water migration.The differences in gaseous water migration between the oil shale residue improved soil and the silty clay before and after freeze-thaw cycles were compared.The internal structural differences between oil shale improved soil and silty soil were also analyzed from a microscopic perspective with the aid of electron scanning microscopy.（3）An indoor unidirectional freezing test was conducted using a coupled waterthermal-force test apparatus for unsaturated soils to monitor the temperature,water content and stress at different locations in the soil column and to measure the thermal conductivity of oil shale improved soil and silty soil before and after freeze-thaw cycles to evaluate the resistance to freezing and swelling of oil shale improved soil and silty soil.（4）The gas diffusion coefficient was applied to gas water migration of unsaturated soil and the frost heaving resistance of the oil shale improved soil was evaluated theoretically.Single-factor and multi-factor prediction models of gaseous water migration quality for oil shale waste residue improvement soil were established to provide theoretical basis for engineering application of oil shale waste improvement soil.