Effective Assessment And Stabilization Mechanism Of Sulfur-free Lignin-stabilized Soda Alkaline Soil

Ensuring the safety and reliability of earth structures such as foundations,embankment dams,canals and rail/road subgrade is one of the main concerns in geotechnical engineering.However,more and more civil engineering structures are inevitably constructed on problematic soils with the rapidly expanding process of urbanization.Therefore,it is very necessary to apply suitable engineering techniques to handle these undesired soils.As a commonly used soil reinforcement technology in geological engineering,soil solidification agent is widely used because of its simplicity,ease of use and relatively low-cost.Although traditional chemical agents can effectively improve the engineering performance of problematic soils,they also cause huge energy consumption and environmental burdens.Therefore,it is necessary to find novel alternative soil additive which is environmental,energy-friendly,low-carbon.As a renewable biomass resource with abundant reserves,lignin has the potential to become an alternative novel soil stabilization agent.This paper proposes to use sulfur-free lignin based which is a low-value by-product of the bioethanol industry as a novel soil stabilization agent to treat silty clay in the western region of Jilin Province.Based on various indoor experiments,it comprehensively reveals the physical and chemical properties,static/dynamic mechanical properties,water stability,micropore and structural properties of sulfur-free lignin stabilized saline soil,and emphasizing the effect of freeze-thaw cycles.It will provide a basic scientific understanding for the further promotion of the use of sulfur-free lignin as a soil additive.The main research conclusions obtained in this thesis are as follows:?1?A comprehensive review of the lignin types,structure and properties and different separation methods,and current commercial applications have been made.Analyze and summarize the related research on using lignin to suppress dust,improve soil strength and durability,and lignin stabilization mechanism.The problems of these literature were also discussed.?2?The basic characteristics of silty clay in western Jilin Province and sulfur-free lignin were analyzed,and a comprehensive research program was performed to finger out the impacts of different sulfur-free lignin content and the number of freeze-thaw cycles on the physical and chemical properties of stabilized soil.The experimental result shows that with the increase of element content,the plasticity index,coarse particle content,cation exchange capacity and organic content of the cured sample increase,while the thermal conductivity gradually decreases.The freeze-thaw cycle mainly serves to break up coarse particles.?3?The stabilized soda-saline soil by sulfur-free lignin shows an unforgettable improvement on unconfined compressive strength,but the strength keeping increases until the content up to 10%and then decreases,which means the optimum content of soda saline soil in western Jilin Province is 10%,the UCS increased by 6 times reaching 1165 k Pa.Moreover,compared with the untreated soil,the failure fracture modes of sulfur-free lignin stabilized soil also show an obvious changed;The 12%and15%sulfur-free lignin stabilized sample shows great improvement in frost resistance;In addition,based on test data,a lignin stabilized soil strength prediction was established.After verification,the model can better predict the strength varies with different lignin content and freeze-thaw cycles.?4?Only considering the effects of lignin content,the electrical resistivity and the longitudinal wave velocity show a negative linear correlation,and both have a good correlation with the compressive strength.Therefore,both of them can be used as an evaluation index for strength development.The strength prediction result according to wave velocity of treated soil is better than that of based on electric resistivity.?5?The dynamic shear modulus of the sample can be increased significantly by adding sulfur-free lignin and increasing the confining pressure and decreased by suffering the freeze-thaw cycle.When the dynamic shear strain amplitude is 0.003,the dynamic shear modulus of 10%stabilized soil decreased by 19.41 MPa after suffering 30 freeze-thaw cycles,implying that the dynamic performance decreases significantly.However,the dynamic shear stress amplitude and dynamic shear modulus are still better than untreated soil at larger strain ranges(10^-3?10^-2)in the condition of no freezing and thawing.?6?Sulfur-free lignin has significantly improved the water stability of silty clay.Under the condition of not undergoing freeze-thaw cycles:10%stabilized soil exhibits the best immersion compressive strength;However,the deterioration effect of freeze-thaw cycles is also significant:all stabilized soils were almost failure after 120freeze-thaw cycles,with UCS less than 100 k Pa.?7?The possible lignin stabilization mechanism is through filling the inter-pores,adsorbing and cementing the soil particles by electrostatic attraction and its own polymer characteristics.During the freeze process,the state of free water changing from liquid to solid causes irreversible damage in soil matrix,thereby reducing the engineering performance of the soil.