Experimental Study On Expansive Soil Engineering Characteristics And Road Use Improvement In Northern Hebei

Expansive soil is a kind of widely distributed special soil,because of its dry shrinkage and wet expansion,repeated expansion and contraction often cause damage to the buildings（structures）built in the expansive soil covered area,which brings a lot of trouble to the construction of the expansive soil area and needs to be effectively treated.In view of the shortcomings of high energy consumption and large pollution in the improvement of traditional lime and cement,based on the concept of green development and in response to the national"dual carbon strategy",this thesis uses industrial solid waste blast furnace slag and a small amount of lime to improve the expansive soil in northern Hebei.Through a series of indoor tests and theoretical analysis such as basic physical and mechanical property test,unconfined compressive strength test and penetration test,the basic physical properties,compaction characteristics,free expansion rate,mechanical properties and permeability properties of expansive soil in northern Hebei were studied.Compared with the traditional cement improvement,the main research contents and conclusions are as follows:（1）The compaction characteristics and water sensitivity characteristics of expansive soil after incorporation of improved materials are studied by compaction experiments,and the results show that the addition of blast furnace slag and lime reduces the maximum dry density of expansive soil and improves the optimal moisture content of expansive soil.Under the same lime content,with the increase of blast furnace slag content,the maximum dry density of improved soil showed a downward trend,and the optimal moisture content showed an increasing trend.Blast furnace slag-lime modified soil is less sensitive to water than plain soil and cement modified soil.（2）Through the free expansion rate test,the variation of free expansion rate with curing age and modifier content was studied.The test results show that the free expansion rate of all the blast furnace slag-lime improved soil is less than 40%for more than 3 days,and it has become a non-expansive soil.Under the same lime content,the free expansion rate of improved soil showed a downward trend with the increase of blast furnace slag content.When 2%lime is added,blast furnace slag-lime improves the expansion characteristics of expansive soil better than cement with the same dosage.（3）Through the unconfined compressive strength test,the influence law of blast furnace slag-lime on the mechanical characteristics and water stability characteristics of expansive soil was obtained,and the road performance of blast furnace slag-lime improved soil was analyzed based on the test results,and the test results showed that the addition of blast furnace slag-lime significantly improved the unimmersed and water-immersed unconfined compressive strength,elastic modulus and water stability of expansive soil.The elastic modulus and water stability showed an increasing trend.Under the 2%lime content,the improvement effect of blast furnace slag-lime on the unconfined compressive strength of expansive soil and the ability to resist deformation under water-immersion conditions was better than that of cement with the same dosage.The improvement effect of blast furnace slag-lime on the water stability performance of expansive soil at the age of 7d and 28d was better than that of cement.The road performance of blast furnace slag-lime improved soil is far better than that of cement improved soil,and the blast furnace slag-lime improved soil meets the strength requirements of the pavement base layer and subbase layer of highway engineering,while the cement improved soil with 4%～12%content does not meet the strength requirements of the highway base layer and subbase layer at all levels stipulated in the specification.（4）Through the permeation test,the change law of the permeability coefficient of the improved expansive soil with the osmotic pressure and the amount of improver was obtained.The blast furnace slag-lime improved soil was compared with the cement improved soil.The test results show that when the osmotic pressure is less than 0.2MPa,the permeability coefficient of the improved soil increases with the increase of pressure,while when the osmotic pressure is stronger than 0.2MPa,the permeability coefficient changes less with the osmotic pressure.Under the same lime content,the penetration of improved soil showed a downward trend with the increase of blast furnace slag content.The permeability coefficients of 7d and 28d of blast furnace slag-lime improved soil are greater than those of cement improved soil,but they are in the order of 10^-6cm/s.The impermeability of cement soil is better than that of Blast furnace slag-lime improved soil with 2%lime content,and the gap becomes more and more obvious with the increase of the amount of improver.For projects with high requirements for impermeability,the amount of lime can be appropriately increased.