| Most of the new problems of the road surface in the seasonally frozen area are subgrade problems.How to deal with these subgrade problems has become a technical problem in the road engineering construction in the northeast of China.However,the former inorganic improver can enhance the frost resistance of subgrade soil in the seasonally frozen area,but it is harmful to the environment.Therefore,it is an urgent problem to find an economic,effective and environmental protection method for subgrade improvement.According to the relevant research at home and abroad,lignin can be added into the soil as an improver to increase the water stability,erosion resistance and frost resistance of the soil.Lignin,as an industrial product,has a huge output in China.However,due to the lack of a reasonable way to use lignin,lignin has been discharged into the river as a waste.Although lignin is not toxic,its aqueous solution has a big smell,which not only wastes but also affects the feelings of people around the waste disposal area.In this paper,the engineering properties and frost resistance of the soil improved by lignin in the seasonal frozen area are explored.Through the study of the strength and microstructure of the soil improved by lignin under the action of freeze-thaw cycle(in this paper,silty soil and silty sand are selected as the soil to be improved by lignin respectively),the micro mechanism of the soil improved by lignin is expounded.On the basis of the above research,a test road is built to verify the improvement of lignin The application effect of seasonally frozen soil subgrade can provide theoretical basis and technical support for the application of lignin improved soil in road engineering in seasonally frozen area,so as to realize the sustainable development of engineering safety and ecological environment.The results are as follows:1.Through heavy compaction test,the maximum dry density of silt is 2.05g/cm3,the optimum moisture content is 7.7%;the maximum dry density of silt sand(SM)is1.97g/cm3,the optimum moisture content is 10.65%.2.The proportion of silt is 2.66;the proportion of silt sand is 2.63.The results show that the influence of lignin on the two kinds of soil is obvious.3.According to the results of particle analysis,the content of clay in the two soils increased gradually with the increase of sodium lignosulfonate content,but there was no obvious change in sand and particle size.4.Before the freeze-thaw cycle,the resistivity of the two kinds of soil increased after lignin was added into the soil;after three and seven freeze-thaw cycles,the resistivity of the two kinds of soil decreased.3.According to the results of particle analysis,the content of clay in the two soils increased gradually with the increase of sodium lignosulfonate content,but there was no obvious change in sand and particle size.5.When sodium lignosulfonate is added into the soil,the p H value of the two improved soils increases first and then tends to be gentle with the increase of the content of lignosulfonate.The p H of sodium lignosulphide is 10.29,that of silty soil is8.95 and that of silty sand is 7.51.6.When the content of lignin in the two soils is 3%-6%,they have better frost resistance,and the recommended content of lignin in the two soils is 3% when considering the economic factors.7.The dynamic resilient modulus of the two kinds of plain soil decreases with the increase of cyclic deviator stress.The larger the confining pressure is,the larger the dynamic modulus of resilience is.The addition of lignin can effectively enhance the antifreezing stability of soil.8.The microstructure analysis shows that the soil particles of the two kinds of soil are loose before adding lignin.After adding lignin,there are cementitious substances among the soil particles and more aggregates.With the increase of freeze-thaw times,the soil structure of the two kinds of soil is affected by thefreeze-thaw damage,but the pores between the particles of the lignin modified soil are uniform and the structure is tight.9.After adding lignin,the porosity of the two improved soils decreased obviously,and the effect of pore improvement was better.10.The horizontal and vertical structural factors,the average structural factors and the average shape factors of the four soils all decrease with the increase of freeze-thaw times,but the anisotropy of the four soils has no obvious regularity.The frost heave rate of four kinds of soil is related to the porosity of the face,and has nothing to do with the average structural factor;while the dynamic modulus of resilience has nothing to do with the porosity of the face,and the microstructure of the associated soil related to the average structural factor affects the expression of its macro properties to some extent. |
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