Study On Compressive Deformation Characteristics And Microstructure Of Loess Under Water Immersion In Yan’an New Area

The compression consolidation and collapse deformation of loess seriously affect the engineering construction and safe operation in loess area.The"gully filling and land making"project in Yan’an New Area is located in loess covered area with high filling height and large filling area.Collapsing deformation occurs under the action of overload and water,which leads to uneven settlement of foundation and deformation and failure of slope.This paper takes Q₃ loess in Yan’an New Area as the research object,and obtains the macroscopic deformation characteristics of loess,such as collapsibility and compression consolidation,through laboratory tests;the mineral composition and microstructure parameters of loess were obtained by scanning electron microscope,mercury injection method,energy spectrum analysis and other testing techniques;the time-effectiveness characteristics of loess compression deformation under the influence of flooding were analyzed by combining macroscopic and microscopic research methods,and the following conclusions were obtained:（1）The loess in the study area belongs to yellowish-brown silty Malan loess.It was found that the leaching rate of soluble salt in soil was fast at first and then slow down.After 10 days of immersion,the leaching amount of soluble salt gradually tended to be stable.（2）Lateral confinement compression consolidation tests were carried out on undisturbed soil and loess with different flooding periods under different water content（10%,12%,14%,16%）,and the compression stress-strain relationship of soil was compared and analyzed;e-p curve,e-logp curve,compressibility coefficient and compressibility modulus were obtained by the soil three-phase index conversion;the hyperbolic model and the power function model are used to fit the compression test results of the flooded loess respectively.It is found that the power function model has better fitting effect than the hyperbolic model when the pressure range is larger;The saturated collapsibility test of loess with different water content and different soaking period was carried out by using the double-line method.The results show that the P-δS curve of loess has a peak value.With the increase of water content,the collapsibility coefficient of loess decreases gradually.With the increase of soaking period,loess collapsibility gradually decreases,and loess collapsibility basically disappears after 10 days of soaking.（3）The particle morphology,contact relationship and pore type of loess were observed by mercury injection and scanning electron microscopy（SEM）tests.The Image Pro Plus 6.0 Image processing system was used to carry out quantitative analysis on the SEM photos of soil samples.A series of microscopic parameters,such as average diameter,circularity,orientation Angle,orientation probability entropy and morphological fractal dimension of soil samples（pores）,were obtained,and the influence of flooding period and water content on the microstructure of loess was analyzed.（4）By using the method of"whole region→micro region→point",the framework particles and cementing materials of undisturbed soil and waterlogged loess were analyzed by energy spectrum,and the morphology,cementing and chemical composition characteristics of five kinds of granular minerals and three kinds of clay minerals were compared and analyzed.