Study On Mechanical Properties And Freeze-thaw Characteristics Of Coal Gangue Improved Loess In Seasonal Freezing Area

Coal gangue is the solid waste produced in the process of coal production and processing,China’s annual output of coal gangue has exceeded 700 million tons,its output is still increasing year by year,but the overall utilization rate is less than 70%,still lower than the comprehensive utilization standard proposed by the state of 75%,and developed countries in Europe and the United States more than 90%of the comprehensive utilization rate compared with there is still a big gap.The contradiction between the rapid growth of coal gangue discharge and the low utilization rate is becoming increasingly prominent,so it is necessary to explore new utilization methods to absorb the increasing coal gangue.Loess is widely distributed in Ningxia,which is characterized by large pores and easy to sink after immersion.In addition,Ningxia is located in northwest China,a typical seasonal frozen soil region,and seasonal frozen soil is sensitive to climate change.The physical and mechanical properties of loess in this region are easily changed under the action of freeze-thaw cycle,which has a serious impact on the strength and stability of soil mass.In loess foundation engineering in seasonal frozen soil area,improved loess is often used as foundation filler.Using coal gangue to improve loess is not only the resource utilization of industrial solid waste,but also the environmental protection while reducing the construction cost.In order to solve the double problems of increasing coal gangue stock and low utilization rate and the disease of loess foundation in seasonal freezing area,this paper proposes to use coal gangue to improve loess as foundation soil.The mechanical properties and freeze-thaw properties directly determine the stability of the foundation in the seasonal frozen soil area.In this paper,unconfined compressive strength test,direct shear test,compression test and consolidation test are carried out to study the mechanical properties of improved loess under different coal gangue content,and the best coal gangue content is selected to improve loess.The freeze-thaw resistance of improved loess with the optimum amount of coal gangue under different freeze-thaw cycles was studied by freeze-thaw cycle test.Finally,the freeze-thaw characteristics of coal gangue improved loess were studied by Comsol finite element software.After analyzing the experimental and numerical simulation results,the following main conclusions are drawn:(1)By studying the mechanical characteristics of the loess modified by coal gangue under different dosage,it is found that the compressive strength,shear strength,cohesion and internal friction Angle of the loess improved by coal gangue increase first and then decrease with the increase of coal gangue dosage,and the compression coefficient and collapsibility coefficient decrease gradually.When the coal gangue content is 20%,the strength characteristic of the loess improved by coal gangue is the best.When the coal gangue content exceeds 15%,the collapsibility of loess is basically eliminated.Considering the mechanical properties and deformation properties of loess improved by coal gangue,the best coal gangue content is 20%.(2)By comparing the quality and strength changes of coal gangue modified loess and plain loess,it is found that the loss rates of mass,compressive strength and shear strength of both plain loess and coal gangue modified loess gradually increase with the increase of freeze-thaw cycles.After 11 freeze-thaw cycles,the loss rates of mass,unconfined compressive strength,shear strength and cohesion of the loess were 1.97%,35.81%,9.63%and 24.31%,respectively,and the internal friction Angle increased by 3.30%.The loss rates of mass,unconfined compressive strength,shear strength and cohesion of coal gangue modified loess are 1.58%,26.87%,7.43%and 18.60%,respectively,and the internal friction Angle is increased by 2.29%.The loss rates of mass loss and strength loss of plain loess are much higher than those of coal gangue modified loess.The results show that the freeze-thaw resistance of coal gangue improved loess is better than that of plain loess,and the effect of freeze-thaw cycle on the internal friction Angle of plain loess and coal gangue improved loess is not obvious.(3)During the freezing process,the temperature and displacement of the coal gangue modified loess soil column are linearly distributed with the height of the soil column,and the unfrozen water content is S-shaped.In the melting stage,the temperature distribution of coal gangue improved loess soil column is"left convex" with height.In the whole freeze-thaw cycle,the distribution of temperature and unfrozen water content with time is concave,and the displacement of coal gangue improved loess with time is convex.The maximum freezing depth of coal gangue improved loess is 6.40cm.The maximum water migration occurred at 37h of freezing,and the lowest unfrozen water content was 16.23cm,and the unfrozen water content was 11.30%.The maximum amount of frost heave occurred at 38.3h of freezing,and the lowest amount of frost heave was at 20cm,and the amount of frost heave was 1.67mm.