Study On Characteristics Of Expansive Soil After Improvement Of Industrial Alkali Slag In Southwest China

Expansive soil has the characteristics of typical water swelling,water shrinkage and cracking.Its basic mineral composition is hydrophilic mineral component,which is a kind of high plasticity special soil.Based on this characteristic of expansive soil,it has a great impact on the safety of buildings built on expansive soil foundations.Therefore,in the construction of expansive soil,it is necessary to conduct research on the characteristics of expansive soil within the scope of the project and carry out relevant improvement measures to meet the needs of engineering construction.Based on the analysis of the basic properties of expansive soils in the old areas of southwest China,this paper further studies the improvement measures for expansive soils in this area.XRD and SEM scanning electron microscopy were used to analyze the microstructure and composition of the old expansive soil.The experiments on basic physical properties and expansion characteristics were used to add cement,lime,industrial alkali residue,cement + industrial alkali residue,lime + industrial alkali residue.The basic physical and expansive characteristics of the expansive soil improved by the five kinds of admixtures.The paper relies on the geotechnical laboratory of Anhui University of Architecture and uses the XRD and SEM scanning electron microscope equipment of Hefei University of Technology to conduct relevant experimental research.Based on the microstructure and composition analysis,it helps to explore more suitable optimization and improvement programs.The details are as follows:(1)The composition and microstructure of expansive soil were analyzed by XRD test and SEM electron microscopy scanning of the expansive soil in Gejiu area,which helped to analyze the basic characteristics and targeted improvement measures of expansive soil.(2)Using the old expansive soil sample and the soil sample modified by adding various materials to improve the basic physical property test and expansion characteristics test,including liquid plastic limit test,particle grading test,compaction test,expansion Force test,free expansion rate test,shear strength test,and collation test data were compared to select the best improvement plan.Research shows:(1)The content of kaolinite and montmorillonite in the old expansive soil is more than half of the total amount reaches 64.62%;the microstructure of theundisturbed expansive soil is matrix microstructure,and it has the characteristics of continuous clay matrix without orientation distribution.The free expansion rate of expansive soil in Gejiu area is 71%,and the content of montmorillonite is 21.74%.According to the index parameters of “Technical Specifications for Buildings in Expansive Soil Construction Areas”,the expansive soil in the old area is identified as the expansive soil with medium expansion potential.(2)Adding cement,lime,industrial alkali slag,cement + industrial alkali slag,lime + industrial alkali slag to improve the old expansive soil,through physical property test and expansion characteristics test,various admixtures All of them have positive effects on the improvement of expansive soil characteristics,among which the improvement effect of industrial alkali residue is most obvious.(3)When the industrial alkali slag blending ratio is 30%,the improved expansive soil particles and grit mass fraction are improved,the clay mass fraction is decreased,the plastic limit is increased to 36.5%,the liquid limit is reduced to 41.8%,and the plasticity is decreased.The index is reduced to 5.3,which is much less than 10;the maximum dry density after industrial alkali slag is improved by 8.3%,the optimum moisture content is reduced by 18%,and the free expansion rate is 5%,compared with the free expansion rate of the undisturbed soil.71% is reduced by about 13 times,the expansion force is reduced to 16 Kpa,and the original expansion force is reduced by about 14 times compared with the original expansion force of 242 Kpa.The suppression effect is very obvious.The internal friction angle of the modified soil is39.64°,and the maximum cohesion is 120.26 KPa.Compared with the undisturbed soil,the degree of improvement is up to 2 times and 16 times respectively,and the improvement effect is very prominent.