Experimental Research On The Physical And Mechanical Property Of Bio-Enzyme-Treated Expansive Soil

Expansive soil is a special kind of cohesive soil,which has the engineering features of expanding when soaked and shrinking when dehydrated.This attribute is detrimental to different engineering projects.Therefore,expansive soil optimizing technology is widely needed in highway construction in areas abounding in this kind of soil.Most existing researches mainly focus on mixing lime,flying ash,cement,weathering sand,soil stabilizers(HEC,HTAB and STW).But there are several unsolved problems:construction difficulties,environment pollution,prohibitive cost,hardness of operation and so on.Based on Hunan traffic science and technology project "Research on the Prediction of Water Damage Influence for Expansive Soil Subgrade under Extreme Climate"(project number 19801-8025),Hunan provincial innovation project for postgraduate students(project number CX2015B308)and Central South University of Forestry and Technology innovation project for postgraduate students(project number CX2015B31)"Experimental Research on Physical and Mechanical Property of Bio-Enzyme-Treated Expansive Soil".By focusing on Louyi highway roadbed expansive soil,experimental study of physical property,features of swelling-shrinkage and mechanical property are presented,with the use of an innovative and practical bio-enzyme-based soil improvement technology.The experimental research examines the influences of the scale of bio-enzyme on variables of physical properties,the stress-strain curve,strength property,and compressibility attribute of treated expansive soil,respectively.The research results propose theoretical foundation for treatment with bio-enzyme of expansive soil physical property,characteristic of swelling-shrinkage and strength.It will provide an efficient,eco-friendly,economical and highly practical bio-enzyme-based soil improvement technology.Contents and results are as follow:1.By experimental study of physical property,the relation between the scale of bio-enzyme and variables such as liquid limit,plastic limit,optimum water content,maximum dry density,and evaluation index are studied.Compared with lime-treated technology,the bio-enzyme-treated technique has better effects in all aspects mentioned above.2.Direct shear test and laboratory tri-axial test are carried out in order to examine the stress-strain relation and strength property of bio-enzyme-treated expansive soil.The change in coefficient of strength increase of bio-enzyme-treated expansive soil with different mixture amounts is scrutinized.Meanwhile,in comparison with lime-treated and cement-treated expansive soil,the bio-enzyme-treated technology is much better to improve coefficient of strength.3.The influential law of the bio-enzyme amount on tangent modulus of elasticity of expansive soil is analyzed in the frame of Duncan-Chang model and data processing of general tri-axial test.According to the experimentation result,the best ratio of mass between enzyme and water is gained4.Through a series of one-dimensional consolidation tests,the effect of consolidation pressure on compressibility attributions of bio-enzyme-treated expansive soil is scrutinized,and voids ratio,compression coefficient and unit settlement are gained.The results are compared with lime-treated and cement-treated experiments.5.By experimental study of free swell ratio,swelling rate with and without load,the relation between the scale of bio-enzyme and these variables are studied.Simultaneously,compared with lime-and cement-treated techniques,the conclusion is drawn that bio-enzyme-treated expansion soil technology is able to promote the attribution of swelling-shrinkage of expansive soil better than lime-treated and cement-treated technology does.