Study On Macro And Micro Characteristics And Modification Mechanism Of Lignin Modified Seasonal Frozen Dispersive Clay

Dispersive clays are widely distributed in seasonal permafrost areas in China,and dispersive clays have become one of the hot spots for special clay research in geotechnical engineering in recent years because of their special characteristics.Due to the principle of homocrystalline replacement and selective adsorption,Ca2+ and Mg2+ in the clay are replaced by Na+,which leads to the increase of the thickness of thin film water on the surface of clay particles,resulting in the increase of the repulsive force between clay particles,and the clay body is easy to produce dispersion and disintegration in water.China’s Songneng Plain contains a large number of dispersive clays.To help develop agricultural irrigation,improve grassland,restore ecological balance and change the natural climate in the arid areas of western Heilongjiang Province,the Heilongjiang Province Southern Diversion Project was built.A large number of water conservancy projects have been built in the distribution area of dispersed clay in the southern part of Heilongjiang province,and due to the easy erosion of dispersed clay,a large number of channel slopes and clay foundations have been damaged,and the freeze-thaw cycle and dry-wet alternation in the seasonal permafrost area have aggravated the dispersive clay engineering damage.Dispersive clay engineering damage is hidden,sudden and difficult to manage.Traditionally,the replacement method and lime modification are often used to treat dispersive clay,but considering the transportation cost and environmental pollution,it is significant to study the deterioration characteristics of dispersive clay in the seasonal permafrost zone and the low cost and environment-friendly modification scheme to improve the quality of dispersive clay engineering in the seasonal permafrost zone.In this paper,we take the dispersive clay of the southern Heilongjiang Province diversion project as the research object to explore the degradation effect of the dispersive clay in the seasonal permafrost zone under the effect of freeze-thaw cycles and alternating wet and dry cycles and the modification mechanism of calcium lignosulfonate on the dispersive clay.The structure changes of dispersive clays were quantified and analyzed by image analysis software Image J and PCAS.The main research contents and conclusions are as follows:(1)Calcium lignosulfonate can effectively reduce the clay dispersion,and it has good modification effect when the lignin dose ≥3%,and the clay dispersion gradually decreases with the increase of lignin dose,but in the case of 0 maintenance,even the dose reaches 10%,it fails to change the clay into non-di spersive clay,and the dispersion of dispersive clay gradually decreases with the extension of calcium lignosulfonate dose and maintenance age,and it first shows the Transitional clay characteristics,and then transformed into non-di spersive clay.When the amount of calcium lignosulfonate≥3%and the maintenance age≥7d,it can produce good modification effect.(2)Under the action of wet and dry cycles,the analysis by Image J image processing software showed that when the lignin dose was 1%～5%,the fracture ratio,average fracture width and total fracture length of the modified clay were reduced to some extent,but when the lignin dose was 10%,the total fracture length of the modified clay had a significant tendency to increase,which indicated that calcium lignosulfonate could effectively reduce the fracture However,the excessive amount of calcium lignin sulfonate will lead to the increase of fine cracks in the clay.3%～5%lignin doping can improve the shear strength of dispersive clay under the action of wet and dry cycles to a certain extent,and the low amount of lignin doping has no obvious effect on the shear strength of the clay,while the excessive amount of lignin doping will lead to the increase of cracks in the clay to form However,excessive lignin admixture will lead to the formation of weak surface and reduce the frictional resistance between clay particles,which will significantly reduce the shear strength and internal friction angle of clay.(3)The pore changes of the modified clay after freeze-thaw cycle and dry-wet cycle were compared by NMR analysis,and it was found that a small amount of lignin incorporation under freeze-thaw cycle could effectively reduce the clay pores,while excessive lignin incorporation would lead to the transformation of small pore size pores into large pore size pores,and the small and medium pore size pores gradually transformed into large pore size pores after freeze-thaw cycle.The lignin incorporation under the dry and wet cycles can effectively reduce the clay pore space,and with the increase of lignin incorporation the modified clay pore space is continuously reduced.(4)Through the scanning electron microscope analysis test,combined with the PCAS image processing software,it was found that a small amount of lignin incorporation can effectively reduce the porosity of the modified clay,and excessive lignin incorporation will lead to the decrease of the number of pores and increase of the porosity of the clay,which will further increase the inhomogeneity of the clay.(5)Through Fourier infrared spectroscopy test,energy spectrum analysis test and existing research data,it is found that lignin generates polymer compounds with certain cementing ability and certain hydrophobic ability through hydrolysis reaction and protonation reaction,which can fill the clay pores and enhance the clay’s water stability and erosion resistance,but too much lignin will lead to the adsorption of its own sulfonic acid group to each other,resulting in the increase of clay viscosity,making it difficult to compact the clay However,too much lignin will lead to the increase of cohesion due to the adsorption of sulfonic acid groups,making the clay difficult to compact and prone to the formation of macropore defects.The analysis of the macro and micro characteristics and modification mechanism of lignin modified dispersed clay in this article can provide theoretical reference for the changes in pore structure and actual engineering performance of dispersed clay.