Experimental Study On Strength Characteristics Of Expansive Soil Improved By Lime-blast Furnace Slag Roadbed

Expansive soil has the characteristics of strong expansion and contraction,which brings a lot of trouble to the promotion of building construction.Aiming at the prevention and control of subgrade soil in expansive soil area,this paper selects the subgrade expansive soil of a provincial road section in Neixiang County,Henan Province as the test soil,and uses lime blast furnace slag as the curing agent to improve the expansive soil.The purpose is to inhibit the swelling and shrinkage of expansive soil and improve the strength of soil.There are two reasons for using lime blast furnace slag as curing agent.On the one hand,lime can stimulate the activity of blast furnace slag and solidify the soil with the cementitious products produced by reaction;On the other hand,blast furnace slag is used as solid waste to improve expansive soil,which improves the recycling rate of solid waste.In order to test the effect of lime blast furnace slag on improving expansive soil,the basic physical and mechanical properties of the improved expansive soil are tested,and compared with the effect of lime metakaolin curing expansive soil,the following conclusions are drawn.(1)Analyze the basic physical and chemical properties of expansive soil and curing agent,and formulate the test plan scientifically.The results of free expansion test show that the free expansion rate of expansive soil is best when the content of lime is 6%,and the free expansion rate of blast furnace slag can be further inhibited.(2)Through the liquid-plastic limit test on expansive soil and improved soil,it can be concluded that the plastic limit increases with the addition of blast furnace slag or metakaolin,while the liquid limit and plastic index decrease;The results of compaction tests on expansive soil and improved soil show that the maximum dry density and water sensitivity of expansive soil decrease obviously with the increase of curing agent content,while the optimal water content increases.(3)Through mechanical properties test study: improved expansive soil stress-strain curve for strain softening model,the compressive strength aspect with the increase of dosage of curing agent,sample destruction of axial stress increases gradually,and the strain produced slightly decreases,and with the increase of curing age,axial stress of the destruction of specimen of further increase.Under the same compressive strength,6%L+6%GGBS can replace6%L+12%MK,and the improved expansive soil of 6%L+3%GGBS and 6%L+3%GGBS meets the minimum bearing capacity standard of the first-class highway subgrade required by the code in the 7-day maintenance period.(4)Through the test with different curing agent content of expansive soil triaxial consolidation undrained shear test conclusion: applying fixed confining pressure,the deviator stress of specimen and cohesion increases with the incorporation of curing agent,when 6% lime and the blast furnace slag or metakaolin content was 12%,the cohesion of the largest,but the internal friction Angle,no obvious regularity,its value stability around 31° Under high confining pressure,the test samples are generally strain-hardening type,and most of them will show swelling failure,while under low confining pressure,the samples are strain-softening type,and have obvious shear failure mode.(5)Through ABAQUS finite element simulation of triaxial consolidation undrained shear test,it can be concluded that when the confining pressure is constant,the peak deviational stress of the sample is positively correlated with the content of curing agent;When the content of curing agent is constant,the peak deviating stress is positively correlated with confining pressure.The results show that the experimental results are in good agreement with the numerical simulation results.