Study On Deformation Characteristics And Microstructure Of Collapsible Loess In Xining Area

Collapsible loess is a typical regional special soil.The stronger the collapsibility of the loess,the larger the amount of collapsing deformation.,the faster and uneven the development,it may occur during the construction and even after the project is completed and operated for decades,which will bring serious disasters to the project.This article takes the strong and weak collapsible loess as the research object,and the cause of the collapsible deformation as the research condition.Study on deformation characteristics and micro-mechanism of collapsible loess in Xining area.It provides a reliable theoretical basis for the experimental research on the reinforcement of collapsible loess foundation with green geopolymers in Qinghai.The main content and conclusions of this article:(1)The uniaxial immersion compression test was used to study the influence of changes in overburden pressure and moisture content on the deformation of strong and weak collapsible loess: compared the deformation curves of strong and weak collapsible loess with collapsing,it was found that the water content increased with humidification.The increase of the rate and overburden pressure,and the collapse deformation curve are all three stages.The deformation of the collapsible loess was significantly larger than that of the weak collapsible loess.This shows that due to the different historical stress conditions,the strength of the strong collapsed loess and the weak collapsed loess are weaker,the joint strength of the framework particles was weaker,the resistance to deformation was weaker,and there are more visible macropores.Therefore,the amount of collapsible deformation and compression deformation of strongly collapsible loess was larger than that of weak collapsible loess.(2)The effects of different principal stress ratios and different humidified moisture contents on the deformation of strong and weak collapsible loess were studied by triaxial immersion compression test: different collapsible deformations of strong and weak collapsible loess under different principal stress ratios.When the principal stress ratio was larger than K,the collapsible strain of the strong and weak collapsible loess dominates,and when the K was smaller,the collapsible shear strain dominates.With the increased of water content,the collapsing strain and collapsing shear strain of strong and weak collapsible loess gradually increased.Strong collapsible loess was weaker than collapsible loess.The inherent structure of the collapsible loess destroyed,it's strength and the rate of decay is high,which was prone to collapsed.Therefore,the strong collapsible loess was weaker than the collapsible loess,and the trend of the collapsing body strain,collapsing axial strain and collapsing shear strain with the increase of humidified water content was generally upward.(3)Analyze the microstructure evolution law of the loess before and after the subsidence by scanning electron microscope and mercury intrusion test: the microstructural changed of strong and weak collapsible loess increased with the moisture content and overburden pressure,after immersion,the arrangement of pores in the loess gradually stabilized,the particle distribution gradually concentrated and the degree of granulation became higher,the pore area ratio gradually decreased,the pore morphology became narrower and narrower,and the cumulative mercury input into the loess gradually decreased.Macro-collapse deformation was manifested by the fact that due to the combined action of water and pressure,the structure is gradually dense and the stability is gradually enhanced,and its collapsibility and compressibility were weakened or vanished.When the principal stress K decreased,as the average principal stress decreased and the shear stress increased,the large pores of strong and weak collapsible loess decreased,the number of mesopores and small pores gradually increased,and the connectivity between pores became worse.At the same time,the connection mode between particles was mainly from point-to-surface contact to surface-to-surface contact.After the strong and weak collapsible loess was soaked in water,the order of the particles became worse,and the distribution fractal dimension gradually increased.Then,the pore area ratio gradually increased and the pore circularity showed a trend of a gentle increased,and the accumulated mercury content of strong and weak collapsible loess gradually decreased.The microstructure of strong and weak collapsible loess with the principal stress ratio has a good correlation with the collapsible deformation law.