Study On The Road Performance Of Fiber Reinforced Cement Solidified Heavy Metal Contaminated Soil

China's economy has developed rapidly since Economic Reform and open up,and the development of highway industry is of great importance to economic development.The total mileage of highway construction increases year by year,and the demand for soil resources for highway construction is huge.At the same time,environmental pollution has become more and more prominent.Industrial pollution,traffic pollution and household garbage pollution all lead to the production of heavy metal contaminated soil,which is undoubtedly a great waste of precious soil resources.As a large agricultural country,there is a large amount of straw left after the crop harvest every year in China,and the most economical and reasonable methods to deal with the left straw are still not invented.Burning is still a mainstream method,but the direct result of burning straw is environmental pollution.Therefore,the research on the treatment of heavy metal contaminated soil and surplus straw will have multiple social significance.Based on the above background,this paper takes heavy metal contaminated soil as the research object,and applies the solidification/stabilization technology and fiber reinforcement technology together to repair and improve the performance of heavy metal contaminated soil.The mechanical properties,leaching properties and durability were considered to study the pavement performance of fiber reinforced cement solidified heavy metal contaminated soil.Firstly,the influences of fiber type,fiber length,fiber content,cement content,curing age,heavy metal ion type and heavy metal ion concentration on the compressive and shear properties of soil were investigated through unconfined compressive strength test and direct shear test.Then,the toxicity leaching test of fiber reinforced cement solidified heavy metal contaminated soil was conducted to explore the synergistic effect of fiber and cement on the fixation and repair of heavy metal ions;Finally,a typical working condition was selected to explore the actual response of soil after the dry-wet cycle and freeze-thaw cycle respectively.Some conclusions are drawn as follows:?1?Adding fiber can improve the brittleness of soil to some extent and improve the residual strength of soil;Different fibers have different effects on the strength.The unconfined compressive strength and shear strength of the soil can be significantly improved by adding polypropylene fiber.However,it does not mean that the more fibers added,the better.When wheat straw fibers with different contents were added,the soil strength was no greater than that of unreinforced soil.Fiber length also has a threshold value.In this paper,the threshold value of polypropylene fiber length is 12mm,and the change of straw fiber length on soil properties is not obvious.The fiber slightly increased the leaching of heavy metal ions.The higher the fiber content was,the shorter the fiber length was,and the higher the leaching concentration of heavy metal ions was.However,the difference in the concentration of heavy metal ions in the leaching solution corresponding to different fiber contents and lengths was not significant.?2?The addition of cement can significantly improve the strength of soil,and the more cement is added,the greater the increase in the strength of soil.The unconfined compressive strength and cohesion of soil are obviously improved,while the increase of internal friction angle is slightly smaller,but at the same time,cement will also increase the brittleness of soil;Cement also has a significant effect on the fixation of heavy metal ions.The higher the cement content is,the lower the leaching concentration of heavy metal ions is.The effect of curing age on soil is similar to that of cement content,the longer the soil sample curing time is,the stronger the soil will be and the better the fixation effect of heavy metal ions will be.?3?The concentration of heavy metal ions in the soil has an impact on the strength and leaching characteristics of the soil.The higher the concentration of heavy metal ions is,the smaller the strength of the soil is,and the higher the leaching ion concentration is.The types of heavy metal ions also have different effects on soil.The solubility of heavy metal salts has a great influence on the characteristics of ion leaching.When the concentration of heavy metal ions is high,the curing effect of cement on Zn²⁺is better than that of Cu²⁺.?4?The influences of Dry-wet cycles and freeze-thaw cycles to the polypropylene reinforced cement solidified contaminated soil are not same,with the increase of dry-wet cycle times,the unconfined compressive strength of polypropylene cement Pb contaminated soil decreased gradually first,then tended to be stable,and with the increase of freeze-thaw cycle times first increases and then decreases slightly,and finally tends to be stable,the same effect is that more dry-wet cycle times and freeze-thaw cycle times will weaken the performance of soil.