Study On Loess Collapsible Characteristics And Model Based On Microscale

The special material and structure composition of loess determine its permeability and collapsibility,which results complex mechanism of collapsibility.With the immersion of collapsible loess,the structure is destroyed to produce significant deformation.Disasters caused by loess collapse has been troubling the engineering construction and safe operation in loess plateau,not only threatening the safety life and property,but restricting the construction and economic development.Therefore,based on the current research progress of the national nature science foundation of China,taking Yan 'an loess as the research object,revealing the loess collapsibility mechanism through laboratory tests,microstructure analysis and XRF test.Finally,establishing a collapsible model with microscopic factors on the basis of theory of damage mechanics and microstructure mutation.This study provides scientific theoretical support and research ideas for the study of the characteristics of loess collapsible.The specific research content is as follows.Firstly,the collapsibility characteristics of loess at different water content,different pressure and different compaction were analyzed at a macro scale.And deriving the relationship between collapsibility coefficient and vertical stress and water content from stresshumidifying deformation surface.Secondly,analyzing the collapsibility characteristics at micro scale,including 2D and 3D microstructure analysis of loess samples under different test conditions.The microstructural changes in the test process were studied from three aspects,which are loess structural unit characteristics,particle connection and pore characteristics.2D and 3D results show collapse of large and medium pores caused by pressure,loss of point contact between particles affected by water,vertical distribution of long axis of particles and disordered distribution of pores provide a sub-stable structure are aspects affecting loess collapsibility on the microscale.After that,the overhead and interconnected pores along the compression direction will collapse under the action of water and pressure.Finally,constructing the collapsible model from macro and micro theory.Damage evolution of loess collapse can be divided into three stages,initial damage,damage stage and complete damage.There are two types of soil in the collapse deformation,undamaged and damaged soil.The stress-strain relation of collapsible loess with microscopic parameters was established by selecting pore ratio macroscopically and 3D porosity microcosmically as damage variables.