| In Kaifeng area,the excavation surface of excavation sites is often lower than the groundwater level and the soil is infiltrated by groundwater.Winter and spring,day and night temperature difference is big,water cut of the remains of the freezing soil melt during the day,night,under the effect of repeated freezing and thawing,the soil moisture migration,freezing expansion and compression damage to the soil,resulting in a decline in soil structure change,the overall stability,and the cause of excavation unloading of soil displacement greatly increase the lateral wall by shear stress of soil,easy to cause serious damage.It is necessary to repair and reinforce the damaged and shed soil in time.However,the soil engineering performance of the site under freeze-thaw cycle is poor,so it needs to be improved by adding natural sisal fiber.In this paper,the improvement effect of sisal fiber on freezing-thawing resistance of site soil was analyzed by frost heaving rate test and direct shear test,and the microstructure changes of sisal fiber improved site soil before and after freezing-thawing were studied by microscopic observation and quantitative analysis.The conclusions are as follows:(1)In the site soil mixed with different quality of sisal fiber is improved,measuring the freeze-thaw cycle test soil samples under the action of frost heaving ratio,found that incorporation of sisal fiber improved site soil frost heave were significantly less than of sisal fiber site soil samples,and the incorporation of sisal fiber content,the more the more freeze-thaw cycles,sisal fibre to the improved effect of frost heave sex,the more obvious.(2)The shear strength of soil decreases with the increase of freezing-thawing times,and the shear strength decreases rapidly with the increase of vertical pressure.When sisal fiber content is 0.1%～0.3%,the shear strength of soil under freeze-thaw cycle can be improved effectively,and when sisal fiber content is 0.2%,the improvement effect is the most significant.Under freeze-thaw cycles,the shear strength of the improved site soil with 0.2% fiber content increased 19.2% on average compared with plain soil.At this time,after nine freeze-thaw cycles,the cohesion of the improved site soil was 15.63 kpa,59.8% higher than that of plain soil,and the internal friction Angle was 22.68°,8.3% higher than that of plain soil.(3)Through XRD analysis,it was found that the addition of sisal fiber did not change the composition of the sample soil,and no obvious new crystal phase appeared in the soil after the addition of sisal fiber,and the microstructure of the soil did not change because of the formation of new substances.By the depth of field microscope and SEM images,the freeze-thaw cycle effect can make the surface of the soil samples have holes,and incorporation of sisal fiber can reduce soil sample pore number after freezing and thawing cycle,the surface elevation difference and pore diameter decreases,and coupling between soil particles more effectively,thus makes the fiber improved site soil frost heave performance enhancements,shear strength increase,the cohesive force of the.(4)By quantitative analysis of soil pores in binarized SEM images,sisal fiber can effectively inhibit the growth rate of average pore diameter under freeze-thaw cycles;Under freeze-thaw cycles,the growth rate of average porosity roundness in sisal fiber improved soil was also slower than that in plain soil.However,the average fractal dimension of soil pores did not change greatly with sisal fiber addition. |
