Study On Engineering Characteristics And Mechanism Of Improved Expansive Soil By Iron Tailings Sand And Calcium Carbide Slag

Expansive soil,also known as "swelling and shrinkage soil",is rich in clay minerals such as montmorillonite and illite.It has strong hydrophilicity and has the characteristics of dry shrinkage and wet swelling,which is extremely harmful to engineering construction.Therefore,in the construction of expansive soil areas,it is necessary to improve the expansive soil to meet the requirements of engineering construction.Iron tailings sand and calcium carbide slag are industrial wastes produced in mining production.Long-term stacking not only pollutes the environment but also is a waste of resources.This research relies on the Anhui Provincial Natural Science Foundation project "Experimental Study on Engineering Properties and Micro-Mechanism of Expansive Soils treated with Iron tailings sand"(No.1608085MD81).Based on the improvement method of industrial waste iron tailings sand and calcium carbide slag composite modified expansive soil,the engineering properties of the improved soil were studied by macroscopic mechanical tests,and the mechanism was explained by microscopic test method.The main results were as follows:(1)When iron tailings sand is used to improve expansive soil alone,with the increase of sand mixing rate,the content of silt and sand in the improved soil increases,and the clay content decreases continuously.The cohesive force first increases and then decreases,reaching the maximum when the sand mixing rate is 30%,and the internal friction angle continuely increases.The compressibility of the improved soil is obviously improved.When the calcium carbide slag is used alone to improve the expansive soil,the optimum moisture content of the improvement effect should be two percentage points higher than the optimum moisture content determined by the compaction test.(2)Compared with the single modifier,the iron tailings sand and calcium carbide slag composite improvement method has a more significant effect on the internal friction angle of the improved soil,and the effect on the cohesion is lower than that of the single-charged calcium carbide slag.With the increase of the immersion time under the condition of long-term immersion,both the cohesive force and internal friction angle of the composite improved soil decrease,and the compressibility increases,however,they all gradually stabilize after 28 days of immersion.(3)The microstructure of the improved soil was observed by SEM test.The iron tailings sand had little effect on the microstructure of the expansive soil,but there was a common crack of about 7 ?m between the sand and the soil.The pore development of the expansive soil after the composite improvement was obviously weakened.The structure of soil was also more dense.The MIP test results showed that the incorporation of iron tailings sand reduced the number of micro-pores in the soil particles and between the soil particles,increased the number of macro-pores.The composite improvement method has a better filling effect on the pores around 7?m.As the age of curing increased,the large and medium pores decreased and the micro-pores increased.The results of the microscopic SEM test and MIP showed a high degree of consistency with the results of the macroscopic mechanical tests.