Research On Mechanical Properties And Chromium Ion Migration Of Chromium Contaminated Soil At Low Temperature

According to the weather and climate characteristics of spring and winter in cold regions of northern China,the mechanical properties of chromium contaminated soils in different low temperature environments,different chromium ion concentrations,different cement and desulfurization gypsum contents and the migration of Cr⁶⁺ at low temperature were studied.The mechanism was analyzed by means of microscopic methods.The main contents were as follows:?1?Through unconfined compressive strength tests on contaminated soils with different temperatures,mix ratios and Cr⁶⁺concentrations,it is found that the unconfined compressive strength increases with the decrease of temperature,and then decreases sharply with the concentration of Cr⁶⁺.The contaminated soils with double mix ratios?cement and desulfurized gypsum?have the best effect,and the deformation modulus is consistent with the strength value of the samples.?2?The displacement frost heave of chromium-contaminated soil in cooling process can be divided into four stages:slow frost shrinkage,rapid frost heave,slow frost heave and stable frost heave.The temperature curve can be divided into four stages:rapid,supercooling,slow and stable.The content of unfrozen water in chromium-contaminated soil presents three stages:supercooled stage,fast frozen stage and slow and stable stage.Most of the unfrozen stage is rapid frozen stage.Water undergoes phase transformation.In the process of low temperature migration of Cr⁶⁺,the content of Cr⁶⁺ is higher at the low temperature end than at the high temperature end,and the concentration at the center is lower than the concentration at the edges of both sides.The area of characteristic peak of T:in chromium-contaminated soils decreases with the decrease of temperature.The macropore represented by>19.8 micron decreases,the mesopore of 0.18-19.8 micron and the small pore of<0.18 micron increase,and the total porosity decreases.The reason for the migration of Cr⁶⁺ is that Freezing into ice crystals,ions in unfrozen water migrate from unfrozen area to growing ice crystals.?3?The micro-structure of chromium-contaminated soil was analyzed by NMR and environmental scanning electron microscopy.The micro-structure of chromium-contaminated soil with appropriate concentration was obviously denser than that of chromium-contaminated soil without or with high concentration of Cr⁶⁺.The strength of chromium-contaminated soil could be improved by appropriate concentration of Cr⁶⁺.