Experimental Study On Strength Characteristics Of Expanded Soil Improved By Steel Slag Powder

Expansive soil,also known as "expansive soil",has the characteristics of swelling and softening when encountering water,and shrinkage when losing water.It often causes uneven vertical settlement and horizontal expansion and contraction deformation of buildings.In this paper,steel slag powder is used as an improved material to carry out Free expansion rate test,liquid plastic limit test,expansion force test,direct shear test test,and triaxial shear test of expansive soil under different dosage,so as to explore the influence of steel slag powder on the expansibility and mechanical properties of expansive soil.The research results can provide a theoretical reference for the treatment of expansive soil foundation in southern Shaanxi.The main research content is as follows:(1)Based on Free expansion rate test,liquid plastic limit test and expansion force test,the influence of different steel slag powder content on expansion and contraction characteristics of expansive soil is obtained.The test shows that with the addition of steel slag powder,the expansion and contraction of soil sample decreases continuously.When steel slag powder is added to 15%,the Free expansion rate decreases by 11%,and the expansion force decreases by 9.5%.The plasticity index decreased by 8%.When the content of steel slag powder exceeds 15%,the improvement effect of the soil sample’s expansion and contraction decreases with the increase of steel slag powder content.It can be concluded that the optimal content of steel slag powder is 15%.(2)Through direct shear test,the influence of different steel slag powder content and water content on the physical and mechanical properties of expansive soil is explored.Research has shown that under certain dosage conditions,the strength parameters of soil samples continuously decrease with the increase of water content;Under certain moisture content conditions,with the addition of steel slag powder,the shear strength,cohesion,and internal friction angle of the soil sample first increase and then decrease.When the content is 15%,the shear strength increases by 17.7%,the cohesion increases by 22.9%,and the internal friction angle increases by 2%.Each strength index reaches its peak.When the content exceeds 15%,the shear strength,cohesion,and internal friction angle show a decreasing trend;Therefore,the optimal dosage of steel slag powder to improve the mechanical properties of expansive soil is 15%.(3)Conduct triaxial shear tests on remolded soil and improved soil under different moisture content,confining pressure,and compaction degree to explore the changes in the(σ1-σ3)-ε1 curve of soil samples under different conditions.Analysis shows that at low confining pressure,low water content,and high compaction,the(σ1-σ3)-ε1 curve of improved soil is mostly strain hardening,while the(σ1-σ3)-ε1 curve of reshaped soil is mostly ideal elastic-plastic;As the confining pressure increases,the(σ1-σ3)-ε1 curves of improved and remolded soils develop towards strain hardening;The main stress difference of the soil sample increases with the increase of compaction and confining pressure,and decreases with the increase of water content.(4)In order to analyze the attenuation law of the strength of improved soil samples with an increase in moisture content and a decrease in compactness,the strength fitting curves of soil samples under different conditions were studied.The study showed that the ability of improved soil to resist strength attenuation with an increase in moisture content and a decrease in compactness was higher than that of remolded soil.This indicates that the water sensitivity of the soil sample decreases and the strength stability of the soil sample increases after the addition of steel slag powder.