Experimental Study On Properties Of Expansive Soil Improved By Multiple Admixtures

In view of the social demand for the disposal of diseases in expansion soil engineering and the resource utilization of solid waste of coltan.In this paper,the expansion deformation and strength characteristics of the composite improved expansion soil of coal zircon powder,fly ash and lime are adopted,and the indoor routine test and SEM test are carried out through orthogonal test design,the sensitivity analysis and curve fitting analysis of the test indicators are carried out to establish the relationship between the amount of doped ash and the test index.The effect and mechanism of effect of multi-doping material on expansion soil improvement were studied,and the optimal doping ratio scheme for improved expansion soil was obtained.It provides scientific basis and effective improvement method for the effective improvement of the expansion of soil road foundation and the resource utilization of coltan.The main contents are as follows:Firstly,the basic physical and chemical properties of the expansion soil and the doping materials are analyzed and the mechanism of expanded soil is improved.Using orthogonal design theory,the experimental design scheme is formulated.The test of the solidification of the glutandu and the soil doused with ash obtained the relationship between the optimal water content and the maximum dry density change of the soil under the mixing ratio,and the optimal water content and maximum dry density of the expanded soil after doping were shown to be on a downward trend.Secondly,through orthogonal design,the coal gangue powder content,fly ash content and lime content are selected as three influencing factors,and various physical and mechanical properties tests are carried out to obtain the liquid plastic limit of expansive soil under the combined action of three factors.The indexes of free expansion,shear strength and unconfined compressive strength have been improved significantly.The results show that the influence of plasticity index on the plasticity index is lime content,fly ash content and coal gangue powder.The effect on free expansion rate,shear strength and unconfined compressive strength is the largest amount of lime and the second addition of coal gangue powder;the factor of improved expansive soil by comprehensive equilibrium method is:lime content>Coal gangue powder content>fly ash content,the optimal mix ratio scheme is A₂B₃C₃,namely 8%of coal gangue powder,11%of fly ash and 6%of lime.The best doping ratio scheme was tested and verified by free expansion rate test and mechanical performance test,and the test index was determined,and the measured value was compared with the results of the mixed ratio scheme and the single doping improved expansion soil,and the accuracy and reliability of the best doping ratio scheme were verified.Finally,according to the scanning electron microscopy test,the microstructure of the modified expansive soil is revealed.The pores of the ash-filled expansive soil particles are mostly filled with spherical particles and white Ca（OH）₂and Ca CO₃crystal grains,which reduces the degree of pore development and the expansive soil is flat.The microstructure of the aggregates and granular particles becomes the granules mainly composed of agglomerates,and the soil structure is more compact,which enhances the stability of the soil and reduces the expansion and contraction deformation.Comprehensive analysis of coal gangue powder,fly ash and lime to improve the mechanism of expansive soil,mainly through ion exchange,agglomeration,carbonation and gelation,and the formation of new substances calcium carbonate,calcium silicate,Calcium aluminate,etc.,in turn to change the internal structure of the soil,reduce the expansion and contraction characteristics of the expansive soil,and enhance its strength.