Laboratory Test On Improvement Of Saline-alkali Soil By Lime And Basalt Fiber

Songnen Plain,the northeastern part of China,contains a large area of saline-alkali soil.The summer is hot and rainy,winter is cold and dry,the special climate leads to soil moisture and salt migration.Soil salinization is increasingly serious,causing harm to road subgrade,canal bank slope and other projects.So it is urgent to improve the mechanical and hydraulic properties of saline-alkali soil,for the future subgrade,canal bank slope and other projects to provide theoretical and parameter basis.In this paper,Jilin Province Matsubara City Qian’an County in the word well saline-alkali soil as the research object.first of all,the basic physical properties of the soil were analyzed,lime and basalt fiber（BF）were selected to improve the saline-alkali soil.The mechanical property experiments（direct shear test,unconfined compression test）and hydraulic property experiments（permeability test,disintegration test）were carried out to analyze the improvement effect of lime and BF.The impacts of curing age and fiber length on the mechanical and hydraulic capabilities of the improved saline-alkali soil were analyzed.Finally,the microstructure and mineral composition of saline soil before and after improvement were studied by SEM and XRD,and the solidification mechanism of improved materials on saline-alkali soil was revealed.The major findings are as follows:（1）The natural density,the maximum dry density,the natural water content,the liquid limit,the plastic limit and the plasticity index of the saline soil in Zhongruzijing are 1.59 g/cm³,1.87g/cm³,12.84%,32%,19.3%and 12.7,respectively.The content of soluble salt in soil sample was0.712%,and the main cation was Na⁺.The anions are mainly HCO₃^-,Cl^-,SO₄^2-.According to Technical Specification for Highway Maintenance and Repair in Saline Soil Area（DB15/T 713-2014）,the soil sample is classified as saline-alkali soil.（2）Based on the direct shear test,the influence of lime and BF content,fiber length and curing age on the shear strength of improved saline-alkali soil are analyzed.The results show that with the increase of lime and BF content,the shear strength of improved saline-alkali soil increases first and then decreases,and the shear strength of improved saline-alkali soil increases with the enhancement of curing age.3%lime and 0.5%BF,fiber length of 6 mm on the improved saline-alkali soil shear strength improvement effect is the best.（3）Based on the unconfined compressive test,the effects of lime and BF content,fiber length and curing age on the unconfined compressive strength（UCS）of improved saline-alkali soil were analyzed.The results show that the UCS of improved saline-alkali soil increases with the increase of lime content.With the increase of BF content and fiber length,the UCS of improved carbonic acid saline soil increases first then decreases,the peak value of fiber content is concentrated at 0.5%and 1%,and the corresponding fiber length is concentrated at 6 mm;Curing age and improved saline-alkali soil UCS is positively correlated.The UCS of 6%lime and 0.5%BF,fiber length 6 mm,curing age 7 days can meet the strength index required by the specification.（4）In the study of permeability of improved saline-alkali soil,the higher the lime content,the smaller the permeability coefficient（PF）of improved saline-alkali soil;The PF of improved saline-alkali soil increases with the increase of BF content.The longer the curing period,the smaller the PF of the improved saline-alkali soil,and the curing period of 1-14 d has a greater impact on the PF of the improved saline-alkali soil.When the fiber length is 6 mm and 9 mm,the PF of the improved saline-alkali soil is the largest.（5）In the disintegration test of the improved saline-alkali soil,the average disintegration rate of the improved saline-alkali soil decreases gradually with the increase of lime content,and the longer the disintegration time,when the lime content is more than 3%,the average disintegration rate of the improved saline-alkali soil decreases greatly.In that condition of sample aft disintegration,the anti-disintegration property of fiber on improve saline-alkali soil needs to be reflected by adding lime,and the effect of fiber on anti-disintegration property of improved saline-alkali soil is not obvious when the content of lime is less than 3%.When lime content is more than 3%,fiber content above 0.5%has a significant effect on improving the disintegration resistance of saline-alkali soil.（6）The samples of saline-alkali soil,3%lime modified saline-alkali soil,3%lime and 0.5%basaltic fiber modified saline-alkali soil were tested by SEM.Lime improves the compactness of the improved carbonate loam and increases the cohesiveness between soil particles.The addition of BF limits the displacement of soil particles and improves the ability of soil to resist deformation.X-ray diffraction（XRD）was used to analyze the mineral composition and content of saline-alkali soil and lime-improved saline-alkali soil.The content of illite and calcite in lime-modified saline-alkali soil is higher than that in saline-alkali soil.These two minerals are cements after lime reaction,which can improve the adhesion between soil particles and improve the mechanical strength and disintegration resistance of improved saline-alkali soil.