Slag+Cement Improved Expanded Soil Project Characterization Study

Swelling soil is a kind of unsaturated soil with multiple fissures,super consolidation and repeated expansion and contraction,and its own strength has the characteristic of decreasing with the increase of water content.With the rapid development of public transportation system,more and more highways and railroads in the construction process will inevitably encounter swelling soil roadbed,due to the reciprocal cyclic effect of vehicles and other dynamic loads,the internal water of swelling soil extruded by external forces can not be discharged,soil strength is reduced,stiffness decay,thus causing roadbed settlement and slope instability and other engineering accidents.Therefore,it is important to improve the expansive soil to meet the actual requirements of the project.The paper takes the swelling soil in southern Shaanxi as the research object,and uses the synergistic effect of slag generated from blast furnace iron making and industrial cement to improve the swelling soil.The law of change of its swelling,static characteristics and dynamic characteristics is studied,and the water sensitivity of the improved soil is explored,which provides theoretical reference for the construction and stability evaluation of road foundation in swelling soil area.The research results are as follows:(1)Liquid-plastic limit,swelling force and free swelling rate tests were conducted on swelling soil in southern Shaanxi,and the effects of different cement + slag admixtures on swelling properties of swelling soil were obtained: cement + slag can effectively reduce the plasticity index,swelling force and free swelling rate of swelling soil and improve the swelling and shrinking properties of swelling soil;with the gradual increase of slag admixture,the improvement effect gradually becomes better,but the growth trend is limited;the improvement effect is better at 5% cement + 10% slag admixture and saves materials.(2)Based on the conventional triaxial test,the changes of shear strength,cohesion and internal friction angle of expanded soil under different cement+slag admixture were obtained:the stress-strain curve of modified expanded soil increased continuously with the increase of surrounding pressure and admixture,the shear strength and cohesion of expanded soil increased with the increase of surrounding pressure and slag admixture,and the growth trend slowed down after the slag admixture exceeded 10%;the internal friction angle of expanded soil was enhanced only after just adding 5% cement,and the change of internal friction angle was not obvious with the increase of slag admixture.(3)The effect of cement+slag doping on the dynamic deformation characteristics of expansive soils was studied by dynamic triaxial tests.The test results show that the dynamic backbone curve gradually increases with the increase of the surrounding pressure and cement+slag admixture,and the dynamic backbone curve does not change significantly after the slag admixture increases to 10%;the dynamic elastic modulus and damping ratio of the expansive soil show an increasing and decreasing trend respectively with the increase of the admixture under the same dynamic strain,and the ability of the soil to resist the dynamic deformation increases significantly.(4)Based on 5% cement + 10% slag admixture,the effect of water content on the mechanical properties of modified expansive soil was obtained: with the increase of admixture and surrounding pressure and the decrease of water content,the stress-strain curve of expansive soil gradually increased and the shear strength increased;with the same admixture,the lower the water content,the higher the cohesion and the larger the angle of internal friction;under the same water content,the angle of internal friction and cohesion of modified expansive soil were always higher than those of plain swelling soil.The incorporation of slag+cement improves the ability of swelling soil to resist water intrusion,and the soil resistance to deformation is enhanced.