Experimental Study On Engineering Properties Of Subgrade Soil In Seasonal Frozen Region Improved By Lignin

The performance of the roadbed,as the foundation of the pavement structure,is linked to the stability and safety of the superstructure.With the rapid development of the economy and society,the standard of road construction and operation is gradually improved,which puts forward higher demands for the performance and stability of roadbed.As a result,it is necessary to improve the roadbed materials using appropriate technical means.Lignin has a promising future as a new type of environmental protection enhancer.Two types of lignin were chosen to improve the soil in this study,and the effects of the type and content of lignin on the improved soil were investigated.Simultaneously,an experimental study on the engineering properties of lignin improved soil under the influence of the freeze-thaw cycle was carried out based on the characteristics of seasonal frozen areas.The following are the main findings of the study:(1)The changes in the basic physical indexes of the soil were similar after the two types of lignin were added to the soil,which decreased the liquid-plastic limit,silt content,specific gravity,p H value,and optimum moisture content,and increased the clay content.Magnesium lignosulfonate raises the maximum dry density of soil,which rises as the content rises.The maximum dry density of calcium lignosulfonate decreased as the calcium lignosulfonate content increased.(2)In the unconfined compressive strength test,the compressive strength of the two kinds of lignin improved soil is higher than plain soil after the freeze-thaw cycle,and the strength attenuation rate is lower than plain soil.Both types of lignin can improve the soil’s freeze-thaw stability,and the maximum value can be achieved with a 1% admixture.The difference is that as the magnesium lignosulfonate content increases,the unconfined compressive strength of improved soil increases at first,then decreases,whereas the unconfined compressive strength of calcium lignosulfonate content decreases.(3)The water absorption and expansion of the two kinds of lignin with 1%content are less than that of plain soil in the California load-bearing ratio test,and the CBR value is higher than plain soil.The water stability of soil can be improved by both types of lignin.Surface cracks in lignin specimens are less,unconfined compressive strength is higher,and the strength loss rate is lower than plain soil after5 dry-wet cycles.When the lignin content is 1 percent,the performance of both lignins is best.(4)With increasing lignin content,the static resilience modulus of the two types of lignin improved soil increased at first,then decreased.The dynamic resilience modulus of plain soil and lignin improved soil increases with increasing bulk stress under the same partial stress.When the confining pressure is increased,the dynamic modulus of resilience increases under the same bias stress,while when the partial stress is increased,the dynamic modulus of resilience decreases under the same confining pressure.The dynamic resilient modulus of calcium lignosulfonate improved soil is higher than that of plain soil under the same stress conditions,but the effect of magnesium lignosulfonate on dynamic resilient modulus is unclear.(5)The dynamic resilience modulus of two types of lignin improved soil is higher than plain soil after a freeze-thaw cycle,and the decrease is smaller than plain soil.The dynamic resilient modulus decreases after the first freeze-thaw cycle and tends to be stable over time.The change law of the freeze-thaw decay rate of dynamic resilient modulus of plain soil and lignin improved soil is similar under the same conditions: the greater the partial stress,the greater the attenuation rate of resilient modulus after freezing and thawing under the same confining pressure.The lower the attenuation rate of resilient modulus after freezing and thawing under the same partial stress,the greater the confining pressure.