Study On Mechanical Properties And Microscopic Mechanism Of Calcium Lignosulfonate Modified Collapsible Loess

The loess is widely distributed in the central and western regions of China.Due to its loose structure and porous structure,the salt in the loess is easy to dissolve under the erosion and infiltration of rainwater,and it shows strong collapsibility,which often causes landslides,foundation instability and other disasters.Therefore,traditional industrial materials such as lime and cement are often used to modify the soil,which can better solve the service performance of the material but will seriously damage the reclamation of the soil.Calcium lignosulfonate from industrial by-products has a good prospect in soil modification balance and environmental protection.In this paper,the collapsibility and mechanical properties of calcium lignosulfonate modified loess were studied based on collapsibility test,grey correlation analysis,compaction test and unconfined compressive strength test,using calcium lignosulfonate as modification additive.The enhancement mechanism of calcium lignosulfonate was investigated by scanning electron microscopy(SEM),energy spectrum analysis(EDS)and X-ray diffraction(XRD).The main research content and conclusion of this paper are described as follows.(1)Based on the collapsibility test,the modified soil with different contents of calcium lignosulfonate was tested by single and double-oedometer methods,and four kinds of physical parameters affecting the collapsibility coefficient were selected for grey correlation analysis.The test results showed that the collapsibility coefficient of the modified soil could be reduced by more than 90% when the content was 3%,which was due to the water repulsion effect of phenylpropane group,and the collapsibility resistance of loess was significantly improved.The order of grey correlation degree of collapsibility on influencing parameters from large to small is moisture content,pore ratio,dry density,and calcium lignosulfonate content.(2)In this study,compaction tests were carried out to study the variation rules of optimal moisture content and maximum dry density of modified soil with different dosages of calcium lignosulfonate.The optimal moisture content of the modified soil was gradually decreased and then increased,while the maximum dry density did not change significantly.In terms of unconfined compressive strength,the effects of different dosage,curing age and water content on the mechanical properties of the modified soil were tested.The results show that the strength of the modified soil increases rapidly in the first 14 days and increases first and then decreases with the content of calcium lignosulfonate.The strength of the modified soil is lower than that of the untreated soil when the content is too high.The strength decreases gradually with the increase of water content and the failure mode changes from brittle fracture to plastic failure.(3)Based on scanning electron microscopy,the microstructure changes of the soil before and after modification were observed,and the changes of chemical elements and mineral composition before and after modification were analyzed by energy spectrum analysis and X-ray diffraction test.The results show that the addition of calcium lignosulfonate does not generate new mineral components,but promotes the formation of carbonate cements,thus filling pores and linking soil particles,reducing the grain size of mineral components and the thickness of electric double layer,and making the microstructure of soil more compact.